Test Japanese encephalitis vaccine shown to be immunogenic and safe

November 29, 2007

A new test vaccine to protect against the Japanese encephalitis virus (JEV) has proven immunogenic and safe in a randomised trial. These are the conclusions of authors of an Article published in this week's edition of The Lancet.

Japanese encephalitis is the most important cause of viral encephalitis in Asia. Although most infections are asymptomatic, JEV can cause serious symptoms such as rigors, fever, headache, neck rigidity and convulsions, and can be fatal. Mortality is much higher in children than adults. JEV is estimated to cause 50000 cases of clinical disease every year, mostly in children under 10 years. It is transmitted through mosquito bites, and is endemic in southeast Asia, although rare outbreaks have occurred in Western Pacific territories of the USA and in Australia. There is only one vaccine against JEV licensed in the USA, Canada, and Australia, and none licensed in Europe. The licensed vaccine is mouse-brain derived, and its routine use in the Japanese childhood vaccination programme is currently suspended due to safety concerns - including allergic reactions. The new test vaccine in this study is purified and inactivated.

Dr Bernd Jilma, Medical University of Vienna, Austria, and colleagues did a trial of 867 adults in the USA, Germany, and Austria. Volunteers were randomised to receive either the JEV test vaccine intramuscularly on a two-dose schedule, or the licensed vaccine subcutaneously according to its recommended three-dose schedule.

The researchers found the safety profile of the test vaccine was good, and its local tolerability profile was more favourable than that of the licensed vaccine. Frequencies of adverse events were similar between treatment groups, with vaccine-related adverse events generally mild. The seroconversion rate for the test vaccine was 98% compared with 95% for the licensed vaccine on day 56. The geometric mean antibody titre (a measure of the immune response) was 244 for recipients of the test vaccine versus 102 for those receiving the licensed vaccine.

The authors note that WHO recommend mass immunisation programmes against JEV for people living in endemic areas. They also draw attention a number of cases reported in international travellers, including from non-endemic countries, and the fact that coverage of such travellers at risk is very low due both a lack of awareness of JEV and fear of potential adverse reactions to the licensed vaccine among those who are aware.

They conclude: "Our direct comparison with the currently licensed vaccine has shown that the Intercell test JEV vaccine is at least equivalent with respect to immunogenicity and antibody titres. Since the clinical efficacy of the licensed vaccine has been shown previously, the non-inferiority results of the test vaccine with respect to serological variables suggest at least an equal clinical efficacy."

In an accompanying Comment, Dr Marc Fischer, National Center for Zoonotic, Vector-borne and Enteric Diseases, Centers for Disease Control and Prevention, Fort Collins, CO, USA, and colleagues say they believe the test vaccine is a promising candidate for use in travellers at risk, and should be further studied for use in children in endemic countries. They also note that there are other promising JE vaccines including a live-attenuated vaccine that is licensed for use in various Asian countries and has been used to vaccinate 30 million children in India and Nepal.

They conclude: "Overall, these new vaccines provide a potential opportunity to further control this disease. With sustained commitment and funding, vaccines against Japanese encephalitis can and should be integrated into routine immunisation programmes in all endemic areas."
-end-
Dr Bernd Jilma, Medical University of Vienna, Austria T) +43 1404002981 / +436508885058 E) bernd.jilma@meduniwien.ac.at

For Dr Marc Fischer, National Center for Zoonotic, Vector-borne and Enteric Diseases, Centers for Disease Control and Prevention, Fort Collins, CO, USA, please contact Lola Russell T) +1 (404) 639-3286 E) mxf2@CDC.GOVThe paper associated with this release can be found at http://multimedia.thelancet.com/pdf/press/Encephalitis.pdf

Lancet

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