Should smallpox virus be destroyed? The relevance of the origins of vaccinia virus

The fate of surviving stocks of smallpox virus is still uncertain, and it is important that arguments in favour of retention or destruction should present balanced evidence. This article balances the view, probably incorrect and possibly alarmist presented earlier in this Journal by Peter Razzell, that vaccinia and cowpox viruses were derived from smallpox virus. The generally accepted alternative view that all three viruses are independent species and that smallpox virus could not emerge through simple mutation of the other two is presented, together with appropriate literature citations.