The first single-dose West Nile virus (WNV) vaccine is now available. Approved by the U.S. Department of Agriculture in the fall of 2006, the new modified live-virus vaccine, called PreveNile, is manufactured by Intervet, Inc.
PreveNile is a chimera vaccine produced by splicing together the yellow fever virus and WNV. The yellow fever virus's ability to replicate is weakened and some of its genes are replaced by genes taken from WNV. The result is a product designed to stimulate WNV immunity without causing disease.
In a study at the University of Florida, 20 horses were vaccinated with the chimera vaccine and 10 horses were left as unvaccinated controls. After 28 days, all of the horses were inoculated with live WNV. All 10 of the unvaccinated horses developed WNV encephalomyelitis; in contrast 19 of the 20 vaccinated horses remained healthy, with the remaining horse experiencing mild and transient ataxia.
The manufacturer reports that the new vaccine is "proven 95 percent effective" and can safely be administered to foals as young as 4 months as well as to horses previously vaccinated with another WNV product. For more information, visit Intervet's PreveNile website. (EQUUS 350, November 2006)