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Japanese Encephalitis Vaccine, Singapore - Shim Clinic

The inactivated mouse-brain-derived (IMB) vaccine is now commonly replaced by cell-culture-based vaccines. The live attenuated SA 14-14-2 vaccine 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 JE vaccine was approved in 2009 in North America, Australia and various European countries. The vaccine is based on the attenuated SA 14-14-2 JE viral strain, inactivated and alum-adjuvanted. 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 safety and immunogenicity. 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. 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 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%. Theses vaccines are currently not available outside Japan.

In addition, a new live attenuated, JE-yellow fever chimeric vaccine has recently been licensed in Australia and Thailand , and will be commercialized from 2012. This vaccine requires a single dose for primary immunization; the possible need for booster doses remains to be determined.

Precautions and contraindications

A hypersensitivity reaction to a previous dose is a contraindication. The live attenuated vaccine should be avoided in pregnancy unless the likely risk favours its administration. Rare, but serious, neurological adverse events attributed to IMB vaccine have been reported from countries or areas at risk as well as from non-risk countries or areas. Allergic reactions to components of the vaccine occur occasionally. As such reactions may occur up to 2 weeks after administration, it is advisable to ensure that the complete course of vaccine is administered well in advance of departure.

Type of vaccine:
1) Live attenuated vaccine (SA 14-14-2 strain)
2) Inactivated, Vero cell-derived, alum-adjuvanted vaccine (SA 14-14-2 strain)
3) Inactivated Vero cell-derived based vaccines (Beijing-1 strain)
Schedule:
1) In China, the first dose of the live attenuated vaccine 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. Protection for several years may be achieved also with a single dose of this vaccine.
2) Primary immunization of the inactivated, alum-adjuvanted vaccine consists of two intramuscular doses, 4 weeks apart
3) The inactivated (Bejjing-1-) vaccines: 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).Booster: The duration of immunity is not well established for the above vaccines. For 1) the live attenuated vaccine, a booster dose is recommended in some countries. For 2) the Japanese vaccines, a booster is recommended after year 1, and thereafter every 3 years. For 3) the inactivated, alum-adjuvanted vaccine, one booster is recommended 12–14 months after completion of the primary immunization; the possible need for further boosters to be determined.

Contraindications: For all JE vaccines: hypersensitivity to a previous dose of vaccine. For live JE vaccine: pregnancy and immunosuppression.

Adverse reactions: Occasional mild local or systemic reactions

Before departure: The immunization series should be completed at least 1 week before potential exposure to JEV.

Special precautions: With the inactivated, alum-adjuvanted, Vero cell-derived SA14-14-2 vaccine, safety and effectiveness have not been established in pregnant women, in nursing mothers, or in children and adolescents (younger than 17 years of age).


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