There is currently no human vaccine for prevention and no specific treatment for West Nile disease. Efforts to reduce the incidence of infection revolve around preventive measures to protect against mosquito bites, the cause of nearly all human infections of the virus.
The Acambis phase II trial is being conducted in more than 200 subjects in the US, and will evaluate the safety, tolerability and immunogenicity of the vaccine at different dose levels in healthy young adults. Once the optimal dose is identified it will be tested in healthy elderly subjects.
So far, the 2005 West Nile virus season in the US has seen 2,775 cases and 98 deaths. According to the Centers for Disease Control and Prevention, all residents in areas where West Nile virus activity has been identified are at risk of getting West Nile encephalitis but people over 50 are at the greatest risk of severe disease.
“West Nile virus is firmly established as an endemic disease in the US and we expect a pattern of recurring epidemic years to continue. 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,” said Dr Thomas Monath, chief scientific officer of Acambis.
In a phase I safety and immunogenicity trial of Acambis’ West Nile virus vaccine, of the subjects who received ChimeriVax-West Nile, 96% in the high-dose group and 100% in the low-dose group developed high titres of West Nile-neutralising antibodies 28 days after vaccination.