Acambis’ has reported positive Phase III results for its candidate vaccine against the viral infection Japanese encephalitis, which affects up to 50,000 people a year and has a death rate of approximately 25%-30%.

Just last year, an outbreak in Northern India and Nepal claimed the lives of 1,200 people, mainly children, and left many others with serious brain damage.

Acambis trials programme for ChimeriVax-JE included a 2,000 patient safety study and an 800-patient efficacy trial in which a single dose of the vaccine was compared to a three-dose regimen of an already-marketed vaccine called JE-VAX from Sanofi Pasteur.

In the 2,000-patient safety trial, the rate of adverse events in a 30-day period after vaccination was similar between ChimeriVax-JE and placebo, with the main side effects associated with the vaccine headache and fatigue. There was one case of febrile illness which resolved without complications.

JE-VAX carries a warning on its label indicating that a delayed allergic reaction can occur within 10 days of injection with the product, even if a prior shot has been tolerated well, and recommending that recipients do not travel to areas with limited access to medical care during that period.

While the efficacy trial is still blinded, Acambis said that the overall seroconversion rate in the study – which is designed to show non-inferiority to the Sanofi Pasteur product - is around 98%.

ChimeriVax-JE is an important new product for Acambis, which needs to find new revenue streams following the completion of a lucrative smallpox vaccine supply deal with the US government.

Earlier this year Novartis entered into a deal with Austrian company Intercell to license rights to a vaccine called IC51 against Japanese encephalitis which started Phase III testing in September 2005.

Shares in Acambis were down slightly (0.8%) on the London Stock Exchange at 146.25 pence in mid-morning trading today.