Japanese Encephalitis - Prevention

Prevention

Infection with JEV confers lifelong immunity. All current vaccines are based on the genotype III virus. A formalin-inactivated mouse-brain derived vaccine was first produced in Japan in the 1930s and was validated for use in Taiwan in the 1960s and in Thailand in the 1980s. The widespread use of vaccine and urbanisation has led to control of the disease in Japan, Korea, Taiwan and Singapore. The high cost of the vaccine, which is grown in live mice, means that poorer countries have not been able to afford to give it as part of a routine immunisation programme.

In the UK, the three vaccines used (two of which are unlicensed) which are JE-Vax, Green Cross and IXIARO (licensed). JE-Vax however has subsequentally been removed from market. JE-Vax and Green Cross require three doses given at 0, 7–14 and 28–30 days. The dose is 1ml for children and adult, and 0.5ml for infants under 36 months of age. IXIARO the new vaccine has been produced by Intercell Biomedical Ltd and requires only 2 doses, and is currently licensed in the U.S., Europe (inc UK), Canada and Australia.

The most common adverse effects are redness and pain at the injection site. Uncommonly, an urticarial reaction can develop about four days after injection. Because the vaccine is produced from mouse brain, there is a risk of autoimmune neurological complications of around 1 per million vaccinations. However in the case of IXIARO where the vaccine is not produced in mouse brains but in vitro using cell culture there is little adverse effects compared to the Placebo, the main side effects are headache and myalgia.

Neutralising antibody persists in the circulation for at least two to three years, and perhaps longer. The total duration of protection is unknown, but because there is no firm evidence for protection beyond three years, boosters are recommended every three years for people who remain at risk . Furthermore there is also no data available regarding the interchangeability of other JE vaccines and IXIARO and recommended those previously immunised with other JE vaccines receive Green Cross or JE-Vax or a primary course of IXIARO.

There are a number of new vaccines under development. The mouse-brain derived vaccine is likely to be replaced by a cell-culture derived vaccine that is both safer and cheaper to produce. China licensed a live attenuated vaccine in 1988 and more than 200 million doses have been given; this vaccine is available in Nepal, Sri Lanka, South Korea and India. There is also a new chimeric vaccine based on the yellow fever 17D vaccine that is currently under development.