This month has seen reports of the sixth death this year in Colorado from the mosquito-borne disease West Nile virus, and it seems that cases will reach record levels in 2003. West Nile virus, which is common in Africa, arrived in New York in 1999, and has since spread across the continent. As Mark Loeb, Associate Professor of Clinical Epidemiology and Biostatistics at the University of McMaster, said, “There's more and more evidence telling us that West Nile is here to stay” (The Globe and Mail). Worryingly, although there have been no cases of the disease in the United Kingdom so far, a recent survey of British birds showed that “an unexpectedly high proportion” contained antibodies specific for the virus (BBC News).

So, the publication (in Proceedings of the National Academy of Sciences) of a successful vaccine study in mice is welcome news. The new DNA vaccine contains a replication-defective, harmless relative of West Nile virus known as Kunjin virus. The authors suggest that this “may provide ... an effective vaccination strategy against further outbreaks” (New Scientist). However, others have raised concerns that this weakened virus might be “more virulent than we believe it is at the moment” (New Scientist). The new vaccine joins two other candidates — a hybrid of yellow fever and West Nile virus, and a hybrid of dengue virus and West Nile virus. None of these vaccines has yet been tested in humans, so as Diane Griffin of Johns Hopkins School of Public Health points out, “it's good to have other candidates in the wings” (Science Now).