Taken at face value the use of vaccines to prevent the effects of serious infections caused by a terrorist attack appears a sensible policy. In 1997 the United States Department of Defense initiated the compulsory anthrax vaccine immunisation programme to immunise 2.4m military personnel.1 In December 2002 a similar programme, also involving civilians, was started against smallpox. In the first five and half months the Department of Defense administered 450 293 doses of smallpox vaccine.2 United States military personnel engaged in military operations in Iraq are immunised against smallpox and anthrax. As in any vaccination campaign, the incidence of the target disease and the characteristics of available vaccines are two key elements in decision making.

Naturally occurring anthrax is a rare disease. It occurs mostly in cutaneous form among those exposed to animal products (such as hides) and causes a rare and rapidly fatal—if untreated—respiratory illness (inhalation anthrax). Inhalation anthrax is the most likely form of the disease in the event of a terror attack as the use of anthrax spores for terror or warfare would probably follow dissemination at high concentration by …