Vaccination against hepatitis A is recommended for all travellers visiting areas outside northwestern Europe, North America, Australia and New Zealand, where the risks of infection from contaminated food and water and close contact with the local population may be high. Those at risk include a wide group of travellers, e.g. short-and long-term travellers, expatriates, aid/health care workers, missionaries and military personnel, and those travellers with underlying medical conditions such as chronic liver disease, where infection with another hepatic virus may result in an increased burden on the liver, leading to morbidity and mortality in this group. The risks of infection with hepatitis A have been estimated as three cases per 1000 travellers per month of travel in a tourist resort, which rises to 20 cases per 1000 travellers per month of travel outside tourist resorts. As the prevalence of infection with hepatitis A has been estimated as 1.4 million cases per annum worldwide, this supports the fact that hepatitis A is the most frequent vaccine-preventable disease in travellers.
The available vaccines are both highly immunogenic and protective when administered intramuscularly at day 0 with a booster at 6-12 months, which confers long-term protection of between 10 and 20 years. Protective levels of hepatitis A antibody are reached within 7-10 days of the primary dose, and immunisation with a single dose of hepatitis vaccine only confers protection for up to 1 year. It is well known that compliance with the first booster at 6-12 months is often poor and so, in terms of practicalities, this first booster dose may be administered safely and effectively at any time after the first dose, which represents the primary course for this vaccine. At present, further booster doses are recommended at 10-yearly intervals but, as this is a highly immunogenic vaccine, further experience is likely to indicate that this may be unnecessary. Recent research has demonstrated the pres ence of protective antibody levels for up to 20 years by using a model of statistical extrapolation determining the kinetics of antibody decay.
As a result of the paradoxical shift in seroprevalence, adults over the age of 40 years, including those who may have a history of jaundice or have lived in an endemic area for several years, may be naturally immune to hepatitis A. In such circumstances, vaccination may not be necessary and natural immunity may be determined by serological testing of the presence of hepatitis A antibodies (IgG).
Both adult (0.1ml) and paediatric (0.5 ml licensed for those over the age of 1 year) vaccine formulations are now available. Minor side-effects, such as swelling and pain at the site of injection, may be experienced, with systemic effects, such as nausea and fever, occurring infrequently. The availability of this immunogenic vaccine should dispense with the use of the hepatitis A immunoglobulin preparation whose immunological properties are much inferior to those of the active vaccine (see below, Im-munoglobulins). Hepatitis A vaccine induces an adequate level of seroprotection within 7-10 days of vaccination and will provide some degree of protection to an individual travelling at short notice, depending upon their risk of exposure. Some travellers may not reach the high-risk destination for several days after immunisation. However, for those travellers who may be exposed more quickly, the human normal immunoglobulin preparation may be used simultaneously, but at a different anatomical site, with the vaccine in order to provide more immediate protection. Recent studies have demonstrated that hepatitis A vaccine is able successfully to prevent outbreaks of disease when used without the immunoglobulin preparation, by providing either protection or attenuation of infection with hepatitis A, which is afforded by use of the vaccine following exposure. This may therefore have implications for the use of hepatitis A vaccine for those travelling at short notice.
A recent communication from the Public Health Laboratory Service in the United Kingdom has recommended that, due to the lack of availability of human normal immunoglobulin, active vaccination using the licensed hepatitis A vaccines is the preferred option for the protection of travellers. Human normal immunoglobulin will only be made available for the protection of household contacts of confirmed cases of hepatitis A and to control outbreaks.
Was this article helpful?