Acambis begins phase 2 study of West Nile virus vaccine

By Angela McDaniels

Seattle, Dec. 20 - Acambis plc said it has started a phase 2 clinical trial of its investigational vaccine against the West Nile virus, ChimeriVax-West Nile.

The company said it is the first to enter a phase 2 trial of a West Nile vaccine.

The randomized, double-blind, placebo-controlled trial is being conducted in more than 200 subjects in the United States. The safety, tolerability and immunogenicity of ChimeriVax-West Nile at different dose levels will be evaluated first in healthy young adults. The optimal dose will subsequently be tested in healthy elderly subjects.

"West Nile virus is firmly established as an endemic disease in the United States and we expect a pattern of recurring epidemic years to continue," chief scientific officer Thomas Monath said in a company news release.

"A vaccine can be a critical part of West Nile disease prevention and epidemic control and Acambis aims, with ChimeriVax-West Nile, to provide a single-dose vaccine to meet this need."

In a phase I safety and immunogenicity trial of ChimeriVax-West Nile, 96% of subjects receiving a high dose of the vaccine and 100% of those receiving a low dose developed high levels of West Nile-neutralizing antibodies 28 days after vaccination, the company said.

Development of ChimeriVax-West Nile was supported by a $3 million grant from the U.S. National Institutes of Health.

While the majority of West Nile infections are mild and do not result in any symptoms, it is estimated that 20% of those infected develop mild symptoms such as fever, headache, body aches and swollen glands. West Nile encephalitis, the more severe form of the infection, is estimated to occur in one out of every 150 of those infected.

So far, the U.S. 2005 West Nile virus season has seen 2,775 cases and 98 deaths, the company said. There is currently no West Nile virus human vaccine and no specific treatment for the disease.

Acambis develops vaccines and is based in Cambridge, Mass., and Cambridge, England.

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