International travel and health

Japanese encephalitis

Vaccine

The inactivated mouse brain-derived (IMB) vaccine is now commonly replaced by cell culture-based vaccines.

A live attenuated vaccine based on the SA 14-14-2 strain of the JE virus is widely used in China and in an increasing number of countries within the Asian region, including India, the Republic of Korea, Sri Lanka, and Thailand.

A Vero cell-derived, inactivated and alum-adjuvanted JE vaccine based on the SA 14-14-2 strain was approved in 2009 in North America, Australia and various European countries. The primary two doses are administered 4 weeks apart. A booster dose is recommended 1–2 years after the primary immunization. This vaccine has been given concomitantly with hepatitis A vaccine without significant interference with the safety and immunogenicity of either vaccine. Data on concomitant administration with other vaccines frequently used in travellers are currently unavailable. The vaccine is licensed for use in individuals 17 years of age and older in the United States, and 18 years and above in other countries. Paediatric and post-marketing safety studies are under way.

Another Vero cell-derived inactivated JE vaccine was licensed by the Japanese authorities in February 2009 and a similar Japanese vaccine was licensed in 2011. These two vaccines use the same strain of JE virus (Beijing-1) as the mouse-brain-derived vaccine. Clinical trials have shown that the vaccines are safe and immunogenic, with seroconversion rates exceeding 95%.

In addition, a new live attenuated, JE–yellow fever chimeric vaccine has recently been licensed in Australia and Thailand. A single dose of this chimeric JE vaccine was found to be safe, highly immunogenic and capable of inducing long-lasting immunity in both preclinical and clinical trials.

Type of vaccine and schedules:
1) Live attenuated vaccine (SA 14-14-2 strain). In China, the first dose is given subcutaneously at age 8 months, followed by a booster dose at 2 years of age. In some areas, an additional booster is offered at 6–7 years of age. However, protection for several years may be achieved with a single dose of this vaccine, and in many countries one dose without subsequent boosters is recommended.

2) Inactivated, Vero cell-derived, alum-adjuvanted vaccine (SA 14- 14-2 strain). Primary immunization consists of two intramuscular doses, 4 weeks apart. A booster is recommended after 1 year.

3) Inactivated Vero cell-derived vaccines (Beijing-1 strain). Primary immunization consists of three doses at days 0, 7 and 28, or two doses given preferably 4 weeks apart (0.25 ml for children <3 years, 0.5 ml for all other ages). One booster is recommended 12–14 months after completion of the primary immunization and thereafter every 3 years.

4) Live chimeric vaccine (with yellow fever 17D as backbone). A single dose is recommended; the need for and timing of a possible booster dose have not yet been determined

Adverse reactions: Occasional mild local or systemic reactions

Contraindications and precautions:
A hypersensitivity reaction to a previous dose is a contraindication.

In principle, the live attenuated vaccine should be avoided in pregnancy unless there is a high risk of exposure to the infection.

Rare, but serious, neurological adverse events attributed to IMB vaccine have been reported, but no causal relationship has been confirmed.

As occasional allergic reactions to components of the vaccine may occur up to 2 weeks after administration, it is advisable to ensure that the complete course of vaccination is administered well in advance of departure.

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