Single-dose of Japanese encephalitis vaccine protects children for over a year

A single-dose of a live vaccine against Japanese encephalitis can give children in Nepal high levels of protection for over a year, according to an article in this week's issue of The Lancet.

Japanese encephalitis is an infection transmitted through the rice-growing areas of Asia by several types of vector mosquito. It causes at least 50000 clinical cases and 10000 deaths every year in Asia. While some Asian countries have nearly eliminated Japanese encephalitis or reduced its incidence, in other countries, such as Nepal and India, the disease has become a substantial public-health problem.

In a previous study in July 1999, Heechoul Ohrr (Yonsei University College, Korea) and colleagues, found that a single dose of live-attenuated SA 14-14-2 Japanese encephalitis vaccine was 99·3% effective in Nepalese children aged 1-15years. In the latest study the team assessed the long-term effect of this vaccine. No additional vaccine was given to the population. An outbreak of the disease was seen in Nepal during August and September 2000. The researchers assessed the situation after this outbreak and found that a single dose of the vaccine had a protective effect of 98·5%12-15months after immunisation.

Professor Ohrr concludes “Because of the large vaccine-eligible population in the AsianPacific region and the short supply of Japanese encephalitis vaccine, the high protective effect of one dose of SA 14-14-2 vaccine lends support to the integration of a single dose, where licensed for use, into the WHO Expanded Programme on Immunisation (EPI) schedule at 12-15 months.”