March 6, 2007

Acambis announced that its investigational single-dose vaccine against Japanese encephalitis (JE), ChimeriVax-JE, has met and exceeded the primary immunogenicity endpoint in a pivotal Phase III efficacy trial.

In the randomized, double-blind, multicenter study, 820 adult subjects were vaccinated at a 1-1 ratio with either Acambis' single-dose ChimeriVax-JE or JE-VAX, the licensed three-dose JE vaccine. The trial was designed to compare the immunogenicity 30 days after immunization with a single dose of ChimeriVax-JE or with three doses of JE-VAX. The subjects received either two doses of placebo followed by one dose of ChimeriVax-JE or the full three-dose schedule of JE-VAX.

The primary efficacy endpoint, seroconversion rates based on neutralizing antibodies against the relevant homologous JE virus, was met, demonstrating the noninferiority of ChimeriVax-JE to JE-VAX. Of the subjects vaccinated with ChimeriVax-JE, 99.1 percent seroconverted compared with 74.8 percent of subjects in the JE-VAX group. The efficacy of ChimeriVax-JE was also shown to be statistically superior to JE-VAX. In addition, ChimeriVax-JE elicited a rapid immune response, with 93.6 percent of those vaccinated with ChimeriVax-JE generating neutralizing antibodies 14 days after vaccination.

Acambis plans to use these Phase III data to support filings for both the endemic and the travel vaccine. The company recently entered into a partnership agreement with sanofi pasteur for the marketing and distribution of ChimeriVax-JE worldwide, excluding India. In India Bharat Biotech International is currently conducting a pediatric trial of ChimeriVax-JE.