To the Editor:
Using a mortality-only model of smallpox vaccination policies, Bozzette et al (1) calculate that pre-emptively vaccinating the general population saves lives if the probability of a high-impact airport attack is greater than 0.01.
However, vaccine-related mortality generally occurs almost immediately, while vaccine-related protection fully lasts, it is thought, 3 to 5 years (2)(3). Thus, pre-emptive vaccination saves lives if the probability of attack is greater than 0.01 over 3 to 5 years, i.e. if the annual probability is 0.002 to 0.003 or higher. The 482 deaths predicted to result from a policy of pre-emptively vaccinating the population approximately equal the deaths from lightning strikes in the United States during a 5-year period (4).
Furthermore, although the attack scenarios used in the model were developed in consultation with experts, the evil ingenuity of some humans should not be underestimated. Attack plans targeting entire cities certainly exist (5). Prudent policy-making would, therefore, model an “Attack Scenario X” which is more lethal than the worst attack experts can publicly discuss.
These considerations make a policy of pre-attack population vaccination more attractive.
1. Bozzette SA, Boer R, Bhatnagar V, et al. A model for a smallpox-vaccination policy. New Engl J Med 2003;348:416-25.
2. http://www.bt.cdc.gov/agent/smallpox/overview/faq.asp, viewed on 9 Feb 2003.
3. Arita I. Duration of immunity after smallpox vaccination: a study on vaccination policy against smallpox bioterrorism in Japan. Jpn J Infect Dis 2002;55:112-6.
4. Lightning-Associated Injuries and Deaths Among Military Personnel --- United States, 1998-2001. MMWR 2002;51:859-862.
5. Alibek K. Biohazard: The Chilling True Story of the Largest Covert Weapons Program in the World -- Told from the Inside by the Man Who Ran It. New York: Delta, 2000; 21.