Vaccine-preventable diseases,
vaccines and vaccination

General considerations

Vaccination is the administration of a vaccine to stimulate a protective immune response that will prevent disease in the vaccinated person if contact with the corresponding infectious agent occurs subsequently. Thus vaccination, if successful, results in immunization: the vaccinated person has been immunized.

In practice, the terms “vaccination” and “immunization” are often used interchangeably.

Disease prevention

Vaccination is a highly effective method of preventing certain infectious diseases.

For the individual, and for society in terms of public health, prevention is better and more cost-effective than cure. Vaccines are generally very safe and adverse reactions are uncommon. Routine immunization programmes protect most of the world’s children from a number of infectious diseases that previously claimed millions of lives each year. For travellers, vaccination offers the possibility of avoiding a number of dangerous infections that may be encountered abroad.

However, vaccines have not yet been developed against several of the most lifethreatening infections, including malaria and HIV/AIDS.

Vaccination and other precautions

Despite their success in preventing disease, vaccines do not fully protect 100% of the recipients. The vaccinated traveller should not assume that there is no risk of catching the disease(s) against which he/she has been vaccinated. All additional precautions against infection (see Chapter 5) should be followed carefully, regardless of any vaccines or other medication that have been administered. These same precautions are important in reducing the risk of acquiring diseases for which no vaccines exist.


Planning before travel
The protective effect of vaccines takes some time to develop following vaccination. The immune response of the vaccinated individual will become fully effective within a period of time that varies according to the vaccine, the number of doses required and whether the individual has previously been vaccinated against the same disease. For this reason, travellers are advised to consult a travel medicine clinic or personal physician 4–6 weeks before departure if the travel destination is one where exposure to any vaccine-preventable diseases may occur.

Vaccine schedules and administration

The vaccines that may be recommended or considered for travellers are shown in Table 6.1. The schedule for administration of each vaccine is given, together with other information for each of the vaccine-preventable diseases. Time intervals for administration of vaccines requiring more than one dose are recommended; some slight variation can be made to accommodate the needs of travellers who may not be able to complete the schedule exactly as recommended. In general, it is acceptable to lengthen the time intervals between doses, but significant shortening of the intervals is not recommended.

The route of administration differs for individual vaccines and is critical for induction of the protective immune response. For injectable vaccines, the route of injectionsubcutaneous, intramuscular or intradermaldetermines the gauge and length of the needle to be used.

Safe injections

The same high standard of injection safety should be applied to the administration of vaccines as to any other injection. A sterile needle and syringe should be used for each injection and disposed of safely.

WHO recommends the use of single-use (“auto-disable”) syringes or disposable monodose preparations whenever possible. Syringes should not be recapped (to avoid needle-stick injuries) and should be disposed of in a way that is safe to the recipient, the provider and the community.

Multiple vaccines

All commonly used vaccines can be given simultaneously at separate sites at least 2 cm apart. However, certain vaccines commonly cause local reactions, which may be accentuated if a number of vaccines are given simultaneously. If possible, these vaccines should be given on separate occasions unless financial and time constraints dictate otherwise. Inactivated vaccines do not generally interfere with other inactivated or live vaccines and can be given simultaneously with, or at any time in relation to, other vaccines without prejudicing immune responses.

A number of combined vaccines are now available, providing protection against more than one disease, and new combinations are likely to become available in future years. For routine vaccination, the combined diphtheria/tetanus/pertussis (DTP) and measles/mumps/rubella (MMR) vaccines are in widespread use in children. Other examples of currently available combination vaccines are hepatitis A+B and hepatitis A + typhoid. In addition, other combination vaccines are available in certain countries: these include IPV+DTP, IPV+DTP+Hib and PV+DTP+HepB+Hib.1

In adults, the combined diphtheria–tetanus vaccine (with reduced diphtheriaTd) is generally used in preference to monovalent (single-disease) vaccine.

Combined vaccines offer important advantages for travellers, by reducing the number of injections required and the amount of time involved, so aiding compliance. Combination vaccines are just as safe and effective as the individual single-disease vaccines.

Choice of vaccines for travel

Vaccines for travellers include: (1) those that are used routinely, particularly in children; (2) others that may be advised before travel; (3) those that, in some situations, are mandatory.

Most of the vaccines that are routinely administered in childhood require periodic booster doses throughout life to maintain an effective level of immunity. Adults in their country of residence often neglect to keep up the schedule of booster vaccinations, particularly if the risk of infection is low. Some older adults may never have been vaccinated at all. It is important to realize that diseases such as diphtheria and poliomyelitis, which no longer occur in most industrialized countries, may be present in those visited by travellers. Pretravel precautions should include booster doses of routine vaccines if the regular schedule has not been followed, or a full course of primary immunization for people who have
never been vaccinated.

1 IPV = inactivated poliomyelitis vaccine; Hib = Haemophilus influenzae type b [vaccine]; HepB = hepatitis B [vaccine].


Other vaccines will be advised on the basis of a travel risk assessment for the individual traveller (see also Chapter 1). In deciding which vaccines would be appropriate, the following factors are to be considered for each vaccine:

• risk of exposure to the disease
  
• age, health status, vaccination history
  
• special risk factors
  
• reactions to previous vaccine doses, allergies
  
• risk of infecting others
  
• cost.
  

Mandatory vaccination, as authorized by the International Health Regulations, nowadays concerns only yellow fever. Yellow fever vaccination is carried out for two different reasons: (1) to protect the individual in areas where there is a risk of yellow fever infection; and (2) to protect vulnerable countries from importation of the yellow fever virus. Travellers should therefore be vaccinated if they visit a country where there is a risk of exposure to yellow fever. They must be vaccinated if they visit a country that requires yellow fever vaccination

Table 6.1 Vaccines for travellers

a OPV = oral poliomyelitis vaccine; IPV = inactivated poliomyelitis vaccine.


as a condition of entry; this condition applies to all travellers who arrive from (including airport transit) a yellow fever endemic country.

Vaccination against meningococcal disease is required by Saudi Arabia for pilgrims visiting Mecca annually (Hajj) or at any time (Umrah) and/or Medina.

Travellers should be provided with a written record of all vaccines administered (patient-retained record), preferably using the international vaccination certificate (which is required in the case of yellow fever vaccination).

Vaccines for routine use

DIPHTHERIA

Disease
Diphtheria is a bacterial disease caused by Corynebacterium diphtheriae. The infection commonly affects the throat and may lead to obstruction of the airways and death. Transmission is from person to person, through close physical contact, and is increased in overcrowded and poor socioeconomic conditions. Exotoxininduced damage occurs to organs such as the heart. Nasal diphtheria may be mild, and chronic carriage of the organism frequently occurs; asymptomatic infections are common. A cutaneous form of diphtheria is common in tropical countries and may be important in transmission of the infection.

Occurrence

Diphtheria is found worldwide, although it is not common in industrialized countries because of long-standing routine use of DTP vaccine. Recently, large epidemics have occurred in several east European countries.

Risk for travellers

Potentially life-threatening illness and severe, lifelong complications are possible in incompletely immunized individuals.

Vaccine

All travellers should be up to date with the vaccine, which is usually given as “triple vaccine”DTP (diphtheria/tetanus/pertussis). After the initial course of three doses, additional doses may be given as DT until 7 years of age, after which a vaccine with reduced diphtheria content (Td) is given. Since both tetanus toxoid (see below) and diphtheria toxoid can reasonably be given on a booster basis about every 10 years, there is little reason to use monovalent diphtheria vaccine.


Precautions and contraindications

Avoid diphtheria-containing vaccines if a severe or life-threatening reaction has occurred to a previous dose. Use a vaccine with reduced diphtheria content (Td) from age 7 years onwards.

TETANUS

Disease

Tetanus is acquired through environmental exposure to the spores of Clostridium tetani, which are present in soil worldwide. The disease is caused by the action of a potent neurotoxin produced by the bacterium in dead tissue (e.g. dirty wounds). Clinical symptoms of tetanus are muscle spasms, initially muscles of mastication causing trismus or “lockjaw”, which results in a characteristic facial expressionrisus sardonicus. Trismus can be followed by sustained spasm of the back muscles (opisthotonus) and by spasms of other muscles. Finally, mild external stimuli may trigger generalized, tetanic seizures, which contribute to the serious complications of tetanus (dysphagia, aspiration pneumonia) and lead to death unless intense supportive treatment is rapidly initiated.

Occurrence

Dirty wounds can become infected with the tetanus spores anywhere in the world.

Risk for travellers

Every traveller should be fully protected against tetanus. Almost any form of injury, from a simple laceration to a motor-vehicle accident, can expose the individual to the spores.

Vaccine

All travellers should be up to date with the vaccine. The primary immunizing course of three doses of DTP is given in the first months of life. Booster doses are most easily given as Td, but certainly all doses given to individuals aged 7 years and above should be Td. A booster dose of Td should generally be used in preference to tetanus toxoid (TT) immediately following trauma. However, no such booster is needed if the last dose was given less than 5 (for dirty wounds) to 10 years (for clean wounds) previously.


Precautions and contraindications

Mild local reactions occur in up to 95% of vaccine recipients. Reactions increase in frequency and severity as the number of doses increases. After booster doses of TT, 50–80% of people experience some pain or tenderness at the injection site. True hypersensitivity reactions to TT occur very rarely.

PERTUSSIS

Disease

Pertussis (whooping cough) is a highly contagious acute bacterial disease involving the respiratory tract and caused by Bordetella pertussis. It is transmitted by direct contact with airborne discharges from the respiratory mucous membranes of infected persons. It causes a severe cough of several weeks’ duration with a characteristic whoop, often with cyanosis and vomiting. In young infants, the cough may be absent and disease may manifest with spells of apnoea.

Although pertussis can occur at any age, most serious cases and fatalities are observed in early infancy and mainly in developing countries. Major complications include pneumonia, encephalitis and malnutrition (due to repeated vomiting). Vaccination is the most rational approach to pertussis control.

Occurrence

Worldwide, B. pertussis causes at least 20 million cases of pertussis, 90% of which occur in developing countries, with an estimated 200 000 to 300 000 fatalities each year.

Risk for travellers

Unprotected infants are at high risk, but all children and young adults are at increased risk if they are not fully immunized. Exposure to pertussis is greater in developing countries, so children up to 7 years of age should be protected by vaccination. Pertussis vaccine is not generally recommended beyond 7 years.

Vaccine

All travellers should be up to date with the vaccine. Both whole-cell (wP) and acellular (aP) pertussis vaccines provide excellent protection. However, protection declines with time and probably extends only a few years. For several decades, wP vaccines have been widely used in national childhood vaccination programmes; aP vaccines, which cause fewer adverse effects, have been developed and are now being licensed in several countries. Both wP and aP are usually administered in combination with diphtheria and tetanus toxoids (DTwP or DTaP). Three doses are required for initial protection.

Precautions and contraindications

Pertussis-containing vaccines are not used after the seventh birthday. Wholecell vaccines should not be given to children with an evolving neurological disease (e.g. uncontrolled epilepsy or progressive encephalopathy). Minor adverse effects such as local redness and swelling and fever are common after wP; prolonged crying and seizures are less common (<1 in 100) and hypotonic–hyporesponsive episodes are uncommon (<1 in 2000). Acellular vaccines cause significantly fewer reactions. The DTaP vaccines have proved to be significantly less reactogenic than the DTwP vaccines in terms of high fever, seizures and hypotonic– hyporesponsiveness episodes. The local reactogenicity of aP vaccines seems to increase with successive doses.

HAEMOPHILUS INFLUENZAE TYPE B

Disease

Haemophilus influenzae type b (Hib) is a common cause of bacterial meningitis and a number of other serious and potentially life-threatening conditions, including pneumonia, epiglottitis, osteomyelitis, septic arthritis and sepsis in infants and older children.


Occurrence
Hib is estimated to cause at least 3 million cases of serious disease and hundreds of thousands of deaths annually, worldwide. The most important manifestations of disease, namely pneumonia and meningitis, are seen mainly in children under 5 years of age, particularly in infants. Rarely occurring in infants under 3 months or after the age of 6 years, the disease burden is highest between 4 and 18 months of age. Hib is the dominant cause of sporadic (non-epidemic) bacterial meningitis in this age group, and is frequently associated with severe neurological sequelae despite prompt and adequate antibiotic treatment. In developing countries, it is estimated that 2–3 million cases of Hib pneumonia occur each year. The disease has practically disappeared in countries where routine vaccination of children is carried out.

Risk for travellers

All unprotected children are at risk at least up to the age of 5 years, and the risk may be increased by travel from a country with relatively low incidence to one where incidence is high.

Vaccine

All children who are not up to date with this vaccine should be offered it. Conjugate Hib vaccines have dramatically reduced the incidence of Hib meningitis in infants and of nasopharyngeal colonization by Hib. The vaccine is often given as a combined preparation with DTP or poliomyelitis vaccine. Hib
vaccine is not yet used routinely in many developing countries where there is continuing high prevalence of the disease.

Precautions and contraindications

No serious side-effects have been recorded, and no contraindications are known, except for occasional hypersensitivity to a previous dose of the vaccine. All conjugate vaccines have an excellent safety record, and, where tested, do not interfere substantially with the immunogenicity of other vaccines given simultaneously.

HEPATITIS B

Disease and occurrence
See Chapter 5.

Risk for travellers

While only certain categories of traveller are clearly at risk because of their planned activities, any traveller may be involved in an accident or medical emergency that requires surgery. The vaccine should be considered for virtually all travellers to areas with moderate to high risk of infection. Travellers who have been immunized (children or adolescents) are protected. It can be administered to infants from birth. At particular risk are those who expose themselves to potentially infected blood or blood-derived fluids, or who have unprotected sexual contact. Principal risky activities include health care (medical, dental, laboratory or other) that entails direct exposure to human blood; receipt of a transfusion of blood that has not been tested for HBV; and dental, medical or other exposure to needles (e.g. acupuncture, piercing, tattooing or injecting drug use) that have not been appropriately sterilized. In addition, in less developed countries, skin lesions in children or adults suffering from impetigo, scabies or scratched insect bites may play a role in disease transmission if there is direct exposure to open wounds.

Vaccine

Hepatitis B vaccine produced both from plasma and by recombinant DNA technology (usually in yeast) is available; the two types are equally safe and effective. Three doses of vaccine constitute the complete series; the first two doses are usually given 1 month apart, with the third dose 1–12 months later. In some countries, a two-dose schedule has been introduced for adolescents, with the second dose given 6–12 months after the first. Immunization provides protection for at least 15 years. Because of the prolonged incubation period of hepatitis B, some protection will be afforded to most travellers following the second dose given before travel, provided that the final dose is given upon return.


If the trip is to be a long one, a schedule of rapid vaccination is preferred (see below). Prevaccination screening to determine immune status is generally not cost-effective in people from industrialized countries, but may be helpful in those from developing countries who have a high probability of having had asymptomatic infection during childhood.

The standard schedule of administration is three doses, given as follows: day 0; 1 month; 6–12 months.

A rapid schedule of administration of monovalent hepatitis B vaccine may be considered as follows: day 0; 1 month; 2 months.

In some countries of the European Union, another rapid schedule has been licensed, with doses given as follows: : day 0; day 7; day 21.

However, if either of the two rapid schedules is used, it is recommended that an additional dose is given after 6–12 months.

A combination vaccine that provides protection against both hepatitis A and hepatitis B may be considered for travellers potentially exposed to both organisms. This inactivated vaccine is administered as follows: day 0; 1 month; 6 months.

Precautions and contraindications

Hepatitis B vaccines are extremely safe. Mild, transient local reactions occur commonly, but anaphylactic reactions are extremely rare. Despite extensive press coverage of the subject, no scientific evidence exists to support the suggestion that hepatitis B vaccine might be a cause of multiple sclerosis.

MEASLES
Disease

Measles is a highly contagious infection; before vaccines became available this disease had affected most people by the time of adolescence. In developing countries, it still causes up to 875 000 deaths annually. The disease typically presents with fever, red rash and runny nose. Common complications include middle-ear infection and pneumonia. Transmission is primarily by large respiratory droplets. Measles is found worldwide, and occurs in a seasonal pattern.

Transmission increases during the late winter and early spring in temperate climates, and after the rainy season in tropical climates. Epidemics occur every 2 or 3 years in areas where there is low vaccine coverage. In countries where measles has been largely eliminated, cases imported from other countries remain an important continuing source of infection.

Occurrence

Measles occurs worldwide, although far fewer cases now occur in industrialized countries and indigenous transmission has virtually stopped in the Americas. Virus transmission still occurs in most tropical countries.

Risk for travellers

Travellers who are not fully immunized against measles are at risk when visiting developing countries.

Vaccine

All travellers from 6 months of age who have not been immunized should be
offered measles vaccine. One dose of vaccine in infancy protects around 80–
90% of recipients for more than 20 years. The measles/mumps/rubella triple
(MMR) or measles/rubella (MR) vaccine is given in many countries instead of
monovalent measles vaccine. The appropriate age for administration is either
9 months or 12–15 months, depending on epidemiological and other factors
relating to all three diseases. Many countries give additional doses either at a
particular age (e.g. 5 years) or during mass campaigns.

Special attention must be paid to all children who have not been vaccinated against
measles at the appropriate time. Measles is still common in many countries and
travel in densely populated areas may favour transmission. For infants travelling
to countries where measles is endemic, a dose of vaccine may be given as early as
6 months of age. However, children who receive the first dose between 6 and


8 months should also receive the scheduled dose at 9 months or 12–15 months of age.

It is generally recommended that individuals with a moderate degree of immune
deficiency receive the vaccine if there is even a low risk of contracting measles
infection from the community. There is a low level of risk in using measles vaccine
in immunocompromised HIV-infected individuals. Where the risk of contracting
measles infection is negligible, physicians who are able to monitor immune status,
for instance CD4 counts, may prefer to avoid the use of measles vaccine.

Precautions and contraindications

Measles vaccine is generally extremely safe. However, since it is a live viral vaccine,
it should be avoided during pregnancy. It should also be avoided if there is a
known allergy to neomycin or gelatin, or if a severe reaction has occurred
following a previous dose of measles (or MR or MMR) vaccine. Very rarely,
encephalitis may follow measles vaccination. Measles vaccine is equally safe and
effective when administered as a single vaccine or in combination. The mumps
component may account for transient parotitis and, rarely, central nervous system
symptoms due to aseptic meningitis. The rubella component may account for
transient lymphadenopathy and, in 25% of rubella-susceptible women, joint
symptoms.

Type of vaccine: Live viral
Number of doses: One, given i.m. or s.c., although many countries
schedule more than one dose for high levels of control
Contraindications: Pregnancy; adverse reaction to previous dose
Adverse reactions: Malaise, fever, rash 5–12 days after vaccination, rarely
encephalopathy
Before departure: 4 weeks
Recommended for: All infants from 9 months of age,1 children, young adults
who have not had at least one dose previously, and
adults who have no documented evidence of previous
vaccination
Special precautions: None
1 Infants travelling to high-risk countries may have an additional dose as early as 6 months
of age, as well as the scheduled dose at 9 or 12–15 months of age.


POLIOMYELITIS
Disease
Poliomyelitis is a disease of the central nervous system caused by three closely
related enteroviruses, poliovirus types 1, 2 and 3. The virus is spread
predominantly by the faecal–oral route, although rare outbreaks caused by
contaminated food or water have occurred. After the virus enters the mouth, the
primary site of infection is the intestine, although the virus can also be found in
the pharynx. Poliomyelitis is also known as “infantile paralysis” because it most
frequently causes paralysis in infants and young children: 60–70% of cases occur
in children under 3 years of age and 90% in children under 5 years of age. The
resulting paralysis is permanent, although some recovery of function is possible
with physiotherapy. There is no cure.
Occurrence
Wild poliovirus transmission has ceased in all industrialized countries and much
of the developing world. The remaining endemic countries in Asia and Africa
are targeted to be free of poliomyelitis by end-2005 (see map). Until all countries
have stopped wild poliovirus transmission, all areas remain at high risk of
importations and even the re-establishment of endemic transmission.
Risk for travellers
Until the disease has been certified as eradicated, the risk of acquiring it remains
and travellers to endemic countries should be fully protected by vaccination. The
consequences of infection are life-threatening or crippling. Infection and paralysis
may occur in non-immune individuals and are by no means confined to infants.
Infected travellers are potent vectors for transmission and possible reintroduction
of the virus into polio-free zones now that worldwide eradication is near.
Vaccine
All travellers should be up to date with vaccination against poliomyelitis. There
are two types of vaccine: inactivated (IPV), which is given by injection, and oral
(OPV). OPV is composed of the three types of live attenuated polioviruses.
Because of the low cost and ease of administration of the vaccine and its
superiority in conferring intestinal immunity, OPV has been the vaccine of choice
for controlling epidemic poliomyelitis in many countries. The immunity
produced by OPV is apparently lifelong.
IPV is used in several European countries and the USA, either as the sole vaccine
against poliomyelitis or in schedules combined with OPV. Although IPV suppresses


pharyngeal excretion of wild poliovirus, this vaccine has only limited effects in
reducing intestinal excretion of poliovirus. For unvaccinated older children and
adults, the second dose is given 1–2 months after the first, and the third 6–12
months after the second. A booster dose is recommended after 4–6 years. IPV is
also the vaccine of choice for travellers with no history of OPV use, as well as for
immunocompromised individuals and their contacts and family members.
For those who have received three or more doses of OPV in the past, it is advisable
to offer another dose of polio vaccine as a once-only dose to those travelling to
endemic areas of the world. Any unimmunized individuals intending to travel
to such an area require a complete course of vaccine. Countries differ in
recommending IPV or OPV in these circumstances: IPV has the advantage of
avoiding any risk of vaccine-associated paralytic poliomyelitis (VAPP), but is
more expensive and may not stop faecal excretion of the virus.
Precautions and contraindications
Both IPV and OPV are very safe vaccines. Reactions to IPV are extremely rare
and tend to be limited to allergic responses among persons already sensitive to
either the formaldehyde or the antibiotics used in the preparation of the vaccine.
The major adverse event associated with OPV is VAPP. The risk of VAPP is
higher after the first dose of OPV than after subsequent doses, ranging from
1 case per 1.4 million to 1 case per 3.4 million first doses administered. VAPP is
more common in individuals who are immunocompromised, for whom IPV is
the vaccine of choice.
Type of vaccine: Live oral (OPV) or killed inactivated injectable (IPV)
Number of doses: Four of OPV; three of IPV
Schedule: OPV at 6, 10 and 14 weeks of age (plus a dose at birth
in endemic countries). IPV at 2, 4 and 12–18 months
Booster: One lifetime dose before travel to endemic countries
Contraindications: None
Adverse reactions: Very rarely VAPP following OPV
Before departure: 4 weeks
Recommended for: All travellers to developing countries where poliomyelitis
is still transmitted
Special precautions: Immunocompromised travellers should receive IPV rather
than OPV


Vaccines for selective use
Vaccines in this section need be offered only to travellers who are going to certain
specified destinations. The decision to recommend a vaccine will depend on a
travel risk assessment for the individual.
CHOLERA
Disease and occurrence
See Chapter 5.
Risk for travellers
Travellers are not at significant risk from cholera provided that simple precautions
are taken to avoid potentially contaminated food and water. Currently available
new vaccines are not necessary for most travellers: the sensible selection of clean
drinking-water and food is more important than vaccination in preventing
cholera, and even the vaccinated traveller should continue to be prudent about
food and drink. Vaccination is advisable for those at increased risk of the disease,
particularly emergency relief and health workers in refugee situations.
Vaccine
Cholera vaccine is not required as a condition of entry to any country. The two
new cholera vaccines (live and killed), given orally, are safe and effective. They
have been licensed and are commercially available in a limited number of
countries, making possible their use as an option for travellers to high-risk
situations in endemic areas. The killed vaccine confers high-grade (85–90%)
protection for 6 months after the second dose. Protection remains as high as
62% after 3 years in vaccine recipients over 5 years of age.
The traditional injectable cholera vaccine conveys incomplete, unreliable
protection of short duration; it is not recommended.
Precautions and contraindications
Antibiotics should be avoided from 1 week before until 1 week after
administration of the live oral attenuated vaccine. Vaccination should be
completed at least 3 days before the first prophylactic dose of mefloquine.


Type of vaccine: Killed and live attenuated oral
Number of doses: Two, 1 week apart (killed vaccine); 1 week (live vaccine)
Contraindications: Hypersensitivity to previous dose
Adverse reactions: Mild local reaction of short duration; mild systemic
reaction
Before to departure: 3 weeks (killed vaccine), 1 week (live vaccine)
Consider for: Travellers with extreme risks (i.e. emergency relief)
Special precautions: No antibiotics from 1 week before until 1 week after
vaccination (live vaccine). Strict precautions regarding
food, water and hygiene
HEPATITIS A
Disease and occurrence
Although hepatitis A is rarely fatal in children and young adults, most infected
adults and some older children become ill and are unable to work for several
weeks or months. The case-fatality rate exceeds 2% among those over 40 years
of age and may be 4% for those aged 60 years or more. (See also Chapter 5.)
Risk for travellers
Hepatitis A is the most common vaccine-preventable infection of travellers.
Travellers from industrialized countries are likely to be susceptible to infection
and should receive the hepatitis A vaccine before travelling to countries with
moderate to high risk of infection. While people travelling to rural areas of
developing countries are at particularly high risk of infection, in practice most
cases occur among travellers staying in resorts and good-quality hotels. People
born and raised in developing countries, and those born before 1945 in
industrialized countries, have often been infected in childhood and are likely to
be immune. For such individuals, it may be cost-effective to test for anti-HAV
antibodies so that unnecessary vaccination can be avoided.
Vaccine
The vaccine should be considered for all travellers to areas with moderate to
high risk of infection and those at high risk of acquiring the disease should be
strongly encouraged to accept vaccination independently of where they travel.
A safe and highly effective inactivated (killed) hepatitis A vaccine became available
in 1992. Since antibodies induced by the vaccine are not detectable until 2 weeks


after administration, travellers should be vaccinated 4 weeks before departure if
possible. A booster dose given 6–24 months later is recommended. This schedule
is expected to provide at least 10 years’ protection.
In the case of emergency travel to a high-risk area, a dose of immunoglobulin
(0.02 ml/kg), where this product is still available, may be considered with the
first dose of vaccine.
A combination hepatitis A/typhoid vaccine is available for those exposed to
waterborne diseases. The vaccine is administered as a single dose, a minimum of
4 weeks before departure, and confers high levels of protection against both
diseases. A second dose of hepatitis A vaccine is needed 6–12 months later and
boosters of typhoid vaccine should be given at 3-yearly intervals.
A combination vaccine that provides protection against both hepatitis A and
hepatitis B may be considered for travellers potentially exposed to both
organisms.
Precautions and contraindications
Minor local and systemic reactions are fairly common.
Type of vaccine: Inactivated, given i.m.
Number of doses: Two
Schedule: Second dose 6–24 months after the first
Booster: May not be necessarymanufacturers propose at
10 years
Contraindications: Hypersensitivity to previous dose
Adverse reactions: Mild local reaction of short duration, mild systemic
reaction
Before departure: Protection 4 weeks after first dose; some protection
immediately after first dose
Recommended for: All non-immune travellers to highly endemic areas
Special precautions: None


INFLUENZA
Disease and occurrence
See Chapter 5.
Risk for travellers
All travellers to areas of the world experiencing a seasonal (winter and spring)
influenza outbreak are at potential risk of contracting the disease. Tourists are at
risk because they often travel in crowded vehicles and visit crowded placesboth
situations that promote transmission. Elderly people, individuals with respiratory
and cardiac disease, diabetes mellitus, or any immunosuppressive condition, and
health care workers are particularly at risk. The impact of an attack of influenza
during travel can range from highly inconvenient to life-threatening.
Vaccine
Influenza viruses constantly evolve, with rapid changes in their antigenic
characteristics. To be effective, influenza vaccines need to stimulate immunity
to the principal strains of virus circulating at the time. The vaccine contains three
strains, with the composition being modified every year to ensure protection
against the strains prevailing in each influenza season. Since the antigenic changes
in circulating influenza viruses occur very rapidly, there may be significant
differences between prevailing strains during the influenza seasons of the northern
and southern hemispheres, which occur at different times of the year (November–
March in the north and April–September in the south). The vaccine composition
is adjusted for the hemisphere in which it will be used. Consequently, vaccine
obtainable in one hemisphere may offer only partial protection against influenza
infection in the other.
Travellers in the high-risk groups for influenza should be regularly vaccinated
each year. Anyone travelling from one hemisphere to the other shortly before,
or early during, the influenza season, should arrange vaccination as soon as
possible after arriving at the travel destination. Vaccine for the opposite
hemisphere is unlikely to be obtainable before arrival.
Precautions and contraindications
Mild local and/or systemic reactions are common. Vaccination is contraindicated
in case of egg allergy.
Type of vaccine: Inactivated non-infectious viral
Number of doses: One, given s.c. or i.m.


Booster: Annual; immunocompromised individuals should receive
a second dose 4 weeks after the first
Contraindications: Hypersensitivity to previous dose or severe hypersensitivity
to egg
Adverse reactions: Local pain and tenderness at injection site (20%), fever,
malaise
Before departure: 2 weeks
Recommended for: High-risk groups before the influenza season, and
optional for travellers to countries currently in influenza
season
Special precautions: None
JAPANESE ENCEPHALITIS
Disease and occurrence
See Chapter 5.
Risk for travellers
The risk of infection with Japanese encephalitis (JE) for travellers to South-East
Asia is low but varies with the season (being higher during the monsoon), the
type of accommodation and the duration of exposure. Short stays in good hotels
with limited likelihood of mosquito bites result in very low levels of risk. In
contrast, campers in rural areas may be at high risk. No more than one case per
year is diagnosed in civilian travellers worldwide.
Vaccine
The vaccine should be considered for all travellers to rural endemic zones if they
intend to stay there for at least 2 weeks. Those at high risk should be strongly
encouraged to accept vaccination. Three types of JE vaccine are currently in
large-scale production and use: inactivated mouse-brain-derived vaccine (IMB),
cell-culture-derived inactivated vaccine and cell-culture-derived live attenuated
vaccine. Only the IMB vaccine is widely commercially available.
Precautions and contraindications
A hypersensitivity reaction to a previous dose is a contraindication. The vaccine
should be avoided in pregnancy unless the likely risk favours its administration.
Rare, but serious, neurological side-effects attributed to IMB vaccine have been
reported from endemic as well as non-endemic regions. Allergic reactions to
components of the vaccine occur occasionally. As such reactions may occur within


2 weeks of administration, it is advisable to ensure that the complete course of
vaccine is administered well in advance of departure.
Type of vaccine: Inactivated mouse-brain-derived
Number of doses: Standard 3-dose schedule or reduced 2-dose schedule, s.c.
Schedule: 3 doses at days 0, 7 and 28; or 2 doses given 1–4
weeks apart (1.0 ml for adults, 0.5 ml for children)
Booster: After 1 year and then 3-yearly
Contraindications: Hypersensitivity to previous dose or to the vaccine
preservative thiomersal
Adverse reactions: Occasional mild local or systemic reaction; occasional
severe reaction with generalized urticaria, hypotension
and collapse
Before departure: At least two doses before departure
Recommended for: Travellers over 1 year of age and staying in endemic
rural areas for more than 2 weeks
Special precautions: Avoiding mosquito bites is as important as being
immunized
LYME DISEASE
Disease and occurrence
See Chapter 5.
Risk for travellers
Travellers at risk include hikers and campers in forested areas of known infested
regions during the tick season (spring to early aumtumn). They may be offered
the vaccine as well as being advised to minimize exposure to ticks by using insect
repellent and wearing clothes that cover as much skin area as possible.
Vaccine
Vaccine is available only in the USA and is strain-specific for that region. The
vaccine is administered intramuscularly in three doses of 0.5 ml at day 0,
1 month and 12 months. The level of seroprotection is 76% after three doses but
only 49% after two doses, clearly indicating that use of the vaccine should be
supplemented by the other methods of personal protection. The vaccine is
licensed for use in those aged 15–70 years and is well tolerated. At present, it is


uncertain whether this vaccine will provide protection against infection with
other strains of B. burgdorferi. Available data indicate that a booster dose of
vaccine will probably be necessary a year after completion of the primary course.
Precautions and contraindications
Only mild reactions are reported after vaccination. Daily checks should be made
for ticks, which should be removed at once. If erythema migrans (an expanding
annular zone of reddening of the skin) is observed, medical guidance should be
sought immediately. Soreness, redness and swelling at the injection site occur
occasionally.
Type of vaccine: Killed, specific for north America
Number of doses: Three, at day 0, 1 month and 12 months
Booster: Probably needed after 1 year
Contraindications: Children under 15 years of age; adverse reaction to previous dose
Adverse reactions: Local side-effects only
Before departure: 2 months
Recommended for: Walkers, campers, etc. in infested countryside
Special precautions: Check daily for ticks and erythema migrans
MENINGOCOCCAL DISEASE

Risk for travellers
Vaccination should be considered for travellers to countries where outbreaks of meningococcal disease are known to occur.
? Travellers to industrialized countries are exposed to the possibility of sporadic cases. Outbreaks of meningococcal C disease occur in schools, colleges, military barracks and other places where large numbers of adolescents and young adults congregate.
? Travellers to the sub-Saharan meningitis belt may be exposed to outbreaks of serogroup A disease with comparatively very high incidence rates during dry season (December–June). Long-term travellers living in close contact with the indigenous population may be at greater risk of infection.

? Pilgrims to Mecca are at risk. The tetravalent vaccine, (A, C, Y, W-135) is currently required by Saudi Arabia for pilgrims visiting Mecca for the Hajj (annual pilgrimage) or for the Umrah.
Vaccine
The vaccine should be offered only to travellers at significant risk of infection (see above). Internationally licensed meningococcal vaccines are bivalent (groups A and C) or tetravalent (groups A, C, Y, and W-135). The vaccines are purified,
heat-stable, lyophilized capsular polysaccharides from meningococci of the respective serogroups. The recommended single dose of the reconstituted vaccine
contains 50 µg of each of the individual polysaccharides.
Both group A and group C vaccines have documented short-term efficacy levels of 85–100% in older children and adults. However, group C vaccines do not prevent disease in children under 2 years of age, and the efficacy of group A vaccine in children under 1 year of age is unclear. Group Y and W-135
polysaccharides have been shown to be immunogenic only in children over 2 years of age.
A monovalent serogroup C conjugate vaccine has recently been licensed for use in children and adolescents. This conjugate (T-cell dependent) vaccine has enhanced immunogenicity particularly for children under 2 years of age.
A protective antibody response occurs within 10 days of vaccination. In
schoolchildren and adults, both group A and group C vaccines appear to provide protection for at least 3 years, but in children under 4 years, the levels of specific antibodies decline rapidly after 2–3 years.
The currently available group A and group C meningococcal vaccines are recommended for immunization of specific risk groups as well as for large-scale immunization, as appropriate, in connection with epidemics of group A or C meningococcal disease. The group A and group C vaccines do not provide any protection against group B meningococci, which are the leading cause of endemic meningococcal disease in some countries.
Precautions and contraindications
These vaccines are safe, and significant systemic reactions have been extremely rare. The most common adverse reactions are erythema and slight pain at the site of injection for 1–2 days. Fever exceeding 38.5 °C occurs in up to 2% of vaccinees. No significant change in safety or reactogenicity has been observed when the different group-specific polysaccharides are combined into bivalent or tetravalent meningococcal vaccines. Cross-protection does not occur and travellers already immunized with conjugate vaccine against serogroup C are not protected against other serogroups.

Those at high risk of type C infection may be vaccinated with the conjugate C vaccine, followed 2 weeks later by the polysaccharide vaccine. All other antigens may be administered simultaneously with the conjugate C vaccine. In the case of other conjugate vaccines containing either diphtheria or tetanus toxoid as the carrier protein, it is advisable to administer at a 1-month interval to avoid enhanced reactogenicity.

Type of vaccine: Purified bacterial capsular polysaccharide
Number of doses: One
Booster: Every 3 years; protection lasts at least 2 years after
infancy
Contraindications: Serious adverse reaction to previous dose
Adverse reactions: Occasional mild local reactions; rarely, slight fever
Before departure: 2 weeks
Consider for: All travellers to countries in the sub-Saharan meningitis
belt, students at risk from endemic disease; Hajj pilgrims
(mandatory)
Special precautions: Children under 2 years of age are not protected by the
vaccine

PNEUMOCOCCAL DISEASE

Disease

The term “pneumococcal disease” refers to a group of clinical conditions caused by the bacterium Streptococcus pneumoniae. Invasive pneumococcal infections include pneumonia, meningitis and febrile bacteraemia; the common non-invasive conditions include otitis media, sinusitis and bronchitis. Infection is acquired by direct person-to-person contact via respiratory droplets or oral contact. There are many healthy, asymptomatic carriers of the bacteria. There is no animal reservoir or insect vector.

Several chronic conditions predispose to serious pneumococcal disease (see below). Increasing pneumococcal resistance to antibiotics underlines the importance of vaccination.


Occurrence
Pneumococcal diseases are a worldwide public health problem. S. pneumoniae is the leading cause of severe pneumonia in children under 5 years of age, causing over 1 million deaths each year, mainly in developing countries. In industrialized countries, most pneumococcal disease occurs in the elderly.

Risk for travellers

Travellers with certain chronic conditions are at increased risk of pneumococcal disease and should be vaccinated. These predisposing conditions include sicklecell disease, other haemoglobinopathies, chronic renal failure, chronic liver disease, immunosuppression after organ transplantation and other etiological factors, asplenia and dysfunctional spleen, leaks of cerebrospinal fluid, diabetes mellitus and HIV infection.
Vaccine
The current polysaccharide vaccines contain capsular antigens of 23 serotypes, which cause 90% of pneumococcal infections. The vaccines are immunogenic in those over 2 years of age. Children under 2 years of age and immunocompromised individuals do not respond well to the vaccine. Vaccination provides a relative protection against pneumococcal pneumonia in healthy elderly individuals.
Pneumococcal vaccine is recommended for selected groups, above the age of 2 years, with increased risk of pneumococcal disease. In some countries, such as the USA, routine vaccination is recommended for everyone aged above 65 years.
A new generation of conjugate pneumococcal vaccines is now being evaluated.
These vaccines contain 9–11 selected polysaccharides bound to a protein carrier, and induce a T-cell-dependent immune response. Conjugate vaccines are likely to be protective even in children below 2 years of age.

Precautions and contraindications
Pneumococcal polysaccharide vaccine is generally considered very safe. Mild, local reactions persisting for up to 48 hours are common; more severe local reactions are unusual. Moderate systemic reactions (e.g. fever and myalgia) are unusual and severe adverse effects (e.g. anaphylactic reactions) are rare.
Revaccination after 3–6 years may be considered for those in certain high-risk groups in whom immunity following vaccination is known to decline rapidly.

Type of vaccine: Polysaccharide
Number of doses: One, given s.c. or i.m.
Booster: Can be considered after 5 years
Contraindications: Adverse reaction to previous dose
Adverse reactions: Mild local reactions
Before departure: 2 weeks
Recommended for: Those at high risk (see text above)
Special precautions: None

RABIES

Risk for travellers

The risk to travellers in endemic areas is proportional to their contact with potentially rabid animals. For instance, it is estimated that 13% of visitors to one country in South-East Asia come into contact with local animals. Veterinary workers and people who work in the streets of big-city slums where dogs roam wild are at the greatest risk. Most travellers in tourist resorts are at very low risk.
There is a greater risk for children, however, who may have more contact with animals and may not report suspect incidents. It is prudent to avoid walking in populated areas where dogs roam. Following suspect contact, especially bites or scratches, medical advice should be sought at once at a competent medical centre, ideally in the capital city. First-aid measures should be started immediately.
Vaccine
Vaccination against rabies is carried out in two distinct situations:
to protect those who are likely to be exposed to rabies, i.e. pre-exposure vaccination; to prevent the establishment of rabies infection after exposure has taken place, usually following the bite of an animal suspected of having rabies,
i.e. post-exposure vaccination.

The vaccines used for pre-exposure and post-exposure vaccination are the same, but the schedule of administration differs according to the type of application.
Modern vaccines of cell-culture origin are safer and more effective than the older vaccines, which were produced in brain tissue, and are now used in most countries.
Pre-exposure immunization should be offered to people at high risk of exposure, such as laboratory staff working with rabies virus, veterinarians, animal handlers and wildlife officers, and to other individuals living or travelling in areas where rabies is endemic. Pre-exposure immunization is advisable for children in endemic areas, where they provide an easy target for rabid animals.

Such immunization should preferably consist of three full intramuscular doses of cell-culture rabies vaccine given on days 0, 7 and 21–28 (a few days’ variation in the timing is not important). For adults, the vaccine should always be administered in the deltoid area of the arm; for young children, the anterolateral area of the thigh is also acceptable. The gluteal area should never be used, since vaccine administration in this area results in lower neutralizing antibody titres.
Where feasible, and particularly in individuals at occupational risk, the presence of virus-neutralizing antibodies should be confirmed using serum samples collected 1–3 weeks after the final dose.

Tissue-culture or purified duck-embryo rabies vaccines of potency at least 2.5 IU/dose induce adequate antibody titres when carefully administered intradermally in 0.1 ml volumes on days 0, 7 and 28. Vaccination by the intradermal route is less immunogenic than intramuscular vaccination, but offers cost savings since the dose is only 0.1 ml per intradermal site. Concurrent use of chloroquine can reduce the antibody response to intradermal human diploid-cell rabies vaccine.
For post-exposure vaccination see Chapter 5.

Precautions and contraindications
Modern rabies vaccines are well tolerated. The frequency of minor adverse reactions (local pain, erythema, swelling and pruritus) varies widely from one report to another. Occasional systemic reactions (malaise, generalized aches and headaches) have been noted after both intramuscular and intradermal injections.

Type of vaccine: Modern vaccine (cell-cultured or embryonated egg
vaccine)
Number of doses: Three, on days 0, 7 and 21–28, given i.m. (1 ml/dose)
or i.d. (0.1 ml/dose)
Booster: Every 2–3 years, depending upon risk of exposure
Contraindications: Severe adverse reaction to previous dose
Adverse reactions: Minor local or systemic reactions
Before departure: Pre-exposure prophylaxis for those planning a prolonged stay or visiting hyperendemic areas, parks and game
reserves in endemic countries
Special precautions: Avoid contact with wild and captive animals and with free-roaming animals, especially dogs and cats
TICK-BORNE ENCEPHALITIS

Risk for travellers
Travellers who walk and camp in infested areas during the tick season (usually spring to early autumn) are at risk and should be vaccinated. Some degree of protection is afforded by clothing that covers as much skin as possible and by applying insect repellent.

Vaccine
The vaccine should be offered only to high-risk travellers. It is an inactivated whole-cell virus vaccine containing a suspension of purified TBE virus grown on chick embryo cells and inactivated with formaldehyde. Two doses of 0.5 ml should be given i.m. 4–12 weeks apart. A third dose is given 9–12 months after the second dose, and confers immunity for 3 years. Booster doses are required to maintain immunity and should be given every 3 years if the risk continues.
Outside endemic countries, the vaccine may be unlicensed and will have to be obtained by special request.
Precautions and contraindications
Occasional local reactions may occur, such as reddening and swelling around the injection site, swelling of the regional lymph nodes or general reactions (e.g. fatigue, pain in the limb, nausea and headache). Rarely, there may be fever above 38 °C for a short time, vomiting or transient rash. In very rare cases, neuritis of varying severity may be seen, although the etiological relationship to vaccination is uncertain. The vaccination has been suspected of aggravating autoimmune diseases such as multiple sclerosis and iridocyclitis, but this remains unproven.
Sensitivity to thiomersal (a vaccine preservative) is a contraindication.
Type of vaccine: Killed
Number of doses: Two, given i.m. 4–12 weeks apart, plus booster
Booster: 9–12 months after second dose
Contraindications: Sensitivity to the vaccine preservative thiomersal;
adverse reaction to previous dose
Adverse reactions: Local reactions occasionally; rarely fever
Before departure: Second dose 2 weeks before departure
Recommended for: High-risk individuals only
Special precautions: Avoid ticks; remove immediately if bitten
TUBERCULOSIS

Risk for travellers
Most travellers are at low risk for tuberculosis (TB). The risk for long-term travellers (>3 months) in a country with a higher incidence of TB than their own may be comparable to the risk for local residents. Living conditions, as well as duration of travel, are important in determining the risk of infection: high-risk settings include health facilities, prisons and shelters for the homeless.
Vaccine
BCG vaccine is of very limited use for travellers. In the first year of life it provides good protection against complications of TB. In countries with high TB prevalence, infants are generally immunized as soon after birth as possible with a single dose of BCG, which protects against severe forms of TB in infancy and early childhood. Other protective benefits of the vaccine are uncertain. BCG should be considered for infants travelling from an area of low incidence to one of high incidence.

For health workers BCG provides some level of protection and one dose should be offered.
Many industrialized countries with a low incidence of TB have ceased giving BCG routinely to neonates; instead, a dose is given in adolescence. Other countries do not use BCG at all but rely on early detection and treatment to control the disease.
Booster doses of BCG are not recommended by WHO.
Precautions and contraindications
BCG is one of the more difficult vaccines to administer and the reconstituted vaccine must be given intradermally. Symptomatic HIV-infected individuals should not be vaccinated.
Type of vaccine: Live bacterial (BCG)
Number of doses: One
Contraindications: Symptomatic HIV infection
Adverse reactions: Local: abscess, regional lymphadenitis.
Distant (rare): osteitis, disseminated disease
Before departure: 4 weeks
Consider for: Infants under 6 months of age travelling to high-risk
countries and health workers
Special precautions: Skin test adults before administration; do not vaccinate if reaction is greater than 5 mm
TYPHOID FEVER

Risk for travellers
All travellers to endemic areas are at potential risk of typhoid fever, although the risk is generally low in tourist and business centres where standards of accommodation, sanitation and food hygiene are high. The risk is particularly high in the Indian subcontinent. Even vaccinated individuals should take care to avoid consumption of potentially contaminated food and water.


Vaccine
Travellers to countries where the risk of typhoid fever is high, especially those staying for longer than a month, those exposed to conditions of poor hygiene, and those visiting the Indian subcontinent and destinations where there is the possibility of antibiotic-resistant organisms, may be offered one of the following vaccines.
? Oral Ty21a. This live attenuated mutant strain of Salmonella typhi Ty21a, supplied as liquid or enteric coated capsules, is given orally in three doses (four in USA) 2 days apart, and produces protection 7 days after the final dose. Seven years after the final dose the protective efficacy is still 67% in residents of endemic areas but may be less for travellers.
? Injectable Vi CPS. Capsular Vi polysaccharide vaccine (Vi CPS), containing
25 µg of polysaccharide per dose, is given i.m. in a single dose and produces protection 7 days after injection. In endemic areas, the protective efficacy is 72% after 1.5 years and 50% 3 years after vaccination.
Both vaccines are safe and effective, currently licensed and available. They offer alternatives to the previous, poorly tolerated, whole-cell typhoid vaccine.
However, their efficacy in children under 2 years of age has not been
demonstrated.
A combined typhoid/hepatitis A vaccine is also available.
Precautions and contraindications
Proguanil, mefloquine and antibiotics should be stopped from 1 week (12 hours in the USA) before starting Ty21a until 1 week after.
Comparison of the adverse effects of typhoid vaccines show that more systemic reactions (e.g. fever) occur after i.m. administration of inactivated vaccine than after either Ty21a or Vi CPS. No serious adverse effects have been reported
following administration of Ty 21A or Vi polysaccharide.
These vaccines are not recommended for use in infant immunization programmes: there is insufficient information on their efficacy in children under 2 years of age.


Type of vaccine: Oral Ty21a and injectable Vi CPS
Number of doses: One of Vi CPS, i.m. Three or four of live Ty21a, given
orally at 2-day intervals as liquid or enteric coated
capsule
Booster: Every 2 to 3 years for Vi CPS, for Ty21a see package
insert
Contraindications: Stop proguanil, mefloquine and antibiotics 1 week
(12 hours in the USA) before starting Ty21a until
1 week after
Adverse reactions: None significant
Before departure: 1 week
Recommended for: Travellers to high-risk areas and travellers staying longer
than 1 month or likely to consume food or beverages
away from the usual tourist routes in developing countries
Special precautions: Vi CPS – not under 2 years of age; avoid proguanil,
mefloquine and antibiotics with Ty21a
YELLOW FEVER
Disease and occurrence

Risk for travellers
The normally low risk to travellers increases with travel to jungle areas in endemic
countries and in or near cities during urban outbreaks. Areas where yellow fever
virus is present far exceed those officially reported. The risk of exposure to
infection can be reduced by taking measures to prevent mosquito bites (see Chapter 3). It should be noted that the mosquito vectors of yellow fever bite mostly during daylight hours.
Vaccine
Yellow fever vaccine is highly effective (approaching 100%), while the disease may be fatal in adults who are not immune. Vaccination is recommended for all travellers (with few exceptions, see below) who visit countries or areas where there is a risk of yellow fever transmission. For domestic travel, vaccination is recommended for travel outside the urban areas of countries in the yellow fever endemic zone (Africa and south America), even if these countries have not officially reported the disease.


Note. Vaccination for personal protection of travellers is not a andatory requirement.
Precautions and contraindications
Tolerance of the vaccine is generally excellentonly 2–5% of vaccine recipients have mild reactions, including myalgia and headache. Contraindications include true allergy to egg protein, cellular immunodeficiency (congenital or acquired, the latter sometimes being only temporary) and symptomatic HIV infection.

Many industrialized countries administer yellow fever vaccine to persons with symptomatic HIV infection provided that the CD4 count is at least 400 cells/mm3.
Asymptomatic HIV-positive individuals may have a reduced response to the vaccine. There is a theoretical risk of harm to the fetus if the vaccine is given during pregnancy, but this must be weighed against the risk to the mother of remaining unvaccinated and travelling to a high-risk zone. (However, pregnant women should be advised not to travel to areas where exposure to yellow fever may occur.) Encephalitis has been reported as a rare event following vaccination of infants under 9 months of age; as a result, administration of the vaccine is not recommended before 9 months of age.

There have been recent reports of a small number of serious adverse reactions, including deaths, following yellow fever vaccination; most of these reactions occurred in elderly persons. However, the risk to unvaccinated individuals who visit endemic countries is far greater than the risk of a vaccine-related adverse event. It remains important for all travellers at risk to be vaccinated; nonetheless, yellow fever vaccination should not be prescribed for individuals who are not at
risk of exposure to infection.
Type of vaccine: Live viral
Number of doses: One priming dose of 0.5 ml
Booster: 10-yearly
Contraindications: Egg allergy; immunodeficiency from medication, disease or symptomatic HIV infection; hypersensitivity to a
previous dose; pregnancy (see text above)
Adverse reactions: Rarely, encephalitis or hepatic failure
Before departure: International certificate of vaccination becomes valid
10 days after vaccination
Recommended for: All travellers to endemic zones and wherever mandatory Special precautions: Not for infants under 9 months of age; restrictions in pregnancy

Mandatory vaccination
Yellow fever
Mandatory vaccination against yellow fever is carried out to prevent the
importation of yellow fever virus into vulnerable countries. These are countries where yellow fever does not occur but where the mosquito vector and nonhuman primate hosts are present. Importation of the virus by an infected traveller could potentially lead to the establishment of infection in mosquitoes and primates, with a consequent risk of infection for the local population. In such cases, vaccination is an entry requirement for all travellers arriving from countries, including airport transit, where there is a risk of yellow fever transmission.
If yellow fever vaccination is contraindicated for medical reasons, a medical certificate is required for exemption.
The international yellow fever vaccination certificate becomes valid 10 days after vaccination and remains valid for a period of 10 years.
For information on countries that require proof of yellow fever vaccination as a condition of entry, see country list.
Travellers should be aware that the absence of a requirement for vaccination does not imply that there is no risk of exposure to yellow fever in the country.
The international certificate of vaccination is reproduced with explanatory notes at the end of the chapter.
Meningococcal disease
Vaccination against meningococcal disease is required by Saudi Arabia for pilgrims visiting Mecca for the Hajj (annual pilgrimage) or for the Umrah.
Following the occurrence of cases of meningococcal disease associated with N. meningitidis W-135 among pilgrims in 2000, the current requirement is for vaccination with tetravalent vaccine (A, C, Y and W-135). Vaccine requirements for Hajj pilgrims are issued each year and published in the Weekly epidemiological record.
Special groups
Infants and young children
Because not all vaccines can be administered to the very young, it is especially important to ensure protection against health hazards such as foodborne illnesses and mosquito bites by means other than vaccination. Some vaccines can be administered in the first few days of life (BCG, oral poliomyelitis vaccine, hepatitis A and B). Others (diphtheria/tetanus/pertussis, diphtheria/tetanus, inactivated poliomyelitis vaccine) should not be given before 6 weeks of age, and yellow fever vaccine not before 9 months of age. Because it may be difficult to reduce children’s exposure to environmental dangers such as placing contaminated objects in the mouth or mosquito bites, it is particularly important to ensure that their routine vaccinations are fully up to date. A child who travels abroad before completing the full schedule of routine vaccines is at risk from vaccine-preventable diseases.
Adolescents and young adults
Adolescents and young adults make up the largest group of travellers and the group most likely to acquire sexually transmitted diseases. They are particularly at risk when travelling on a limited budget and using accommodation of poor standard (e.g. when backpacking), as well as from a lifestyle that may include risky sexual behaviour and other risks taken under the influence of alcohol or drugs. Because risk reduction through behaviour modification may not be reliable, this age group should be strongly encouraged to accept all appropriate vaccines before travel and to adhere to other precautions for avoiding infectious diseases.
Frequent travellers
Individuals who travel widely, usually by air, often become lax about taking precautions regarding their health. Having travelled numerous times without major health upsets, they may neglect to check that they are up to date with vaccination. Such travellers pose a special problem for health advisers who should, nonetheless, encourage compliance.
Last-minute travellers
Certain individuals, including emergency aid and health care workers, may need to travel at very short notice to dangerous, often war-torn countries. It may be difficult to give them multiple vaccines in a short space of time. If some vaccines have not been administered by the time of departure, it may be possible for the traveller to carry the doses safely in a vacuum flask (with or without ice, depending on the required temperature for the vaccine), together with the appropriate injection devices. Vaccines should travel well like this until they can be stored at the appropriate temperature at the destination, awaiting timely use.
If there is any doubt about being able to keep vaccines cold in transit, the traveller should be encouraged to obtain the remaining doses in the country of destination after the appropriate interval.
Those in occupations that make the need for emergency travel likely to arise should be strongly encouraged to keep their routine and other recommended vaccinations fully up to date.
Pregnancy
Pregnancy should not deter a woman from receiving vaccines that are safe and will protect both her health and that of her child. However, care must be taken to avoid the inappropriate administration of certain vaccines that could harm

Table 6.2 Vaccination in pregnancy
Vaccine Use in pregnancy Comments
BCGa No
Cholera Safety not determined
Hepatitis A Yes, administer if indicated Safety not determined
Hepatitis B Yes, administer if indicated
Influenza Yes, administer if indicated In some circumstances
consult a physician
Japanese encephalitis Safety not determined
Measlesa No
Meningococcal disease Yes, administer if indicated
Mumpsa No
Poliomyelitis OPV Yes, administer if indicated
IPV Yes, administer if indicated Normally avoided
Rubellaa No
Tetanus/diphtheria Yes, administer if indicated
Rabies Yes, administer if indicated
Typhoid Ty21a Safety not determined
Varicellaa No
Yellow fevera Yes, administer if indicated Avoided unless at high risk
a Live vaccineto be avoided during pregnancy.
the unborn baby. Killed or inactivated vaccines, toxoids and polysaccharides can generally be given during pregnancy, as can oral polio vaccine. Live vaccines are generally contraindicated because of largely theoretical risks to the baby.
Measles, mumps, rubella, BCG and yellow fever vaccines should be avoided in pregnancy. The risks and benefits should nevertheless be examined in each individual case. Vaccination against yellow fever may be considered after the sixth month of pregnancy when the risk from exposure is deemed greater than the risk to the fetus (see Table 6.2). However, pregnant women should be advised not to travel to areas where there is a risk of exposure to yellow fever.
Elderly travellers
Vaccination of healthy elderly travellers does not differ in principle from
vaccination of younger adults. However, special considerations arise if the elderly traveller has not been fully immunized in the past and/or has existing medical problems.
Many elderly people may have never been vaccinated with the vaccines used in routine childhood immunization programmes, or may have neglected to keep up the recommended schedule of booster doses. As a consequence, they may be susceptible to diseases such as diphtheria, tetanus and poliomyelitis as well as to other infections present at the travel destination.
Elderly travellers who have never been vaccinated should be offered a full primary course of vaccination against diphtheria, tetanus, poliomyelitis and hepatitis B.
In addition, those who are not immune to hepatitis A should be vaccinated against this disease before travelling to a developing country.
Since the elderly are at risk for severe and complicated influenza, regular annual vaccination is recommended. For travellers from one hemisphere to the other, vaccine against the currently circulating strains of influenza is unlikely to be obtainable before arrival at the travel destination. Those arriving shortly before, or early during, the influenza season, and planning to stay for more than 2–3 weeks, should arrange vaccination as soon as possible after arrival. Pneumococcal
vaccine should also be considered for elderly travellers in view of the risk of pneumococcal pneumonia following influenza infection.
Special considerations arise in the case of elderly travellers with pre-existing chronic health problems (see below).

Travellers with chronic medical problems
Travellers with chronic medical conditions involving impaired immunity,
including cancer, diabetes mellitus, HIV infection and treatment with immunosuppressive drugs, may be at risk of severe complications following administration of vaccines that contain live organisms. Consequently, it may be advisable to avoid measles, oral polio, yellow fever and BCG vaccines for these travellers.

For travel to a country where yellow fever vaccination is mandatory, a medical certificate will be required to obtain exemption.

Travellers with chronic cardiovascular and/or respiratory conditions or diabetes mellitus are at high risk for severe influenza and its complications. Regular annual vaccination against influenza is recommended. For travel from one hemisphere to the other shortly before, or early, during the influenza season, vaccination should be sought as soon as possible after arrival at the travel destination.

For those who lack a functional spleen, additional vaccines are advised: Hib, meningococcal vaccine (conjugate C as well as A+C or quadrivalent vaccine) and pneumococcal vaccination should be considered, in addition to regular vaccination against influenza.
HIV-positive and immunocompromised travellers

The likelihood of successful immunization is reduced in some HIV-infected children and adults, but the risk of serious adverse effects remains low.
Asymptomatic HIV-infected children should be immunized according to
standard schedules. With certain exceptions, symptomatic HIV-positive
individuals should also be immunized as usual. Both measles and oral
poliomyelitis vaccines may be given to persons with symptomatic HIV infection, but special attention should be paid to measles vaccination. Some vaccinations are contraindicated for this group:
? Measles vaccine has generally been recommended for individuals with
moderate immunodeficiency if there is even a low risk of contracting wild measles from the community. A low level of risk is associated with use of measles vaccine in individuals who are HIV-infected and whose immune system is impaired. Where the risk of contracting wild measles infection is negligible, it may be preferable to avoid use of the vaccine.
? Yellow fever vaccine is not recommended for symptomatic HIV-positive adults and children. It is not certain whether yellow fever vaccine poses a risk for asymptomatic HIV-infected persons. Any adverse reactions to the vaccine occurring in HIV-positive individuals should be reported to WHO. In many industrialized countries, yellow fever vaccine is administered to people with symptomatic HIV infection or suffering from other immunodeficiency diseases, provided that their CD4 count is at least 400 cells/mm3 a