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The number of cases spread from each case in the German and Yugoslav outbreaks did not vary from 11 to 38. The majority of cases yielded zero spread. Even in the completely missed first generation of the Yugoslav outbreak, only two patients spread smallpox to more than four others.
The suggestion that 100,000 to 1 million deaths might occur from smallpox in the United States is implausible. The cumulative annual rates of attack in areas of the Asian subcontinent where the disease was hyperendemic were never more than 180 per million per year.2 Isolation and ring vaccination would rapidly contain an outbreak once recognized. Finally, Dark Winter has been discredited as a portrayal of smallpox epidemiology by the work of Meltzer et al.4 (which is cited by Bicknell) and by other models.
Today, widespread infection with the human immunodeficiency virus, post-transplantation immunosuppression, and increasingly prevalent eczema would raise the number of deaths from vaccination to a value considerably higher than the 180 that Bicknell estimates from 1968 data. In the absence of a creditable terrorist threat, the risks of vaccination continue to outweigh its benefits.
J. Michael Lane, M.D., M.P.H.
869 Clifton Rd.
Atlanta, GA 30307-1223
mikelane869{at}yahoo.com
References
To the Editor: Resuming smallpox vaccination is a necessary strategic decision. Lane assumes that the risk of smallpox is very small and that ring vaccination after an attack would work — a best-case scenario. Terrorism, when the risk of attack is unknown but not trivial, requires planning for a worst case.
A 25 percent death rate from smallpox is not avoidable. However, preexposure vaccination risks can be minimized by using a semipermeable membrane dressing and by excluding children under 10 years of age, immunocompromised persons, and those with dermatitis.1 Vaccinating now would make any postattack control strategy easier, could deter an attack, and would be safer for everyone than acting later, in crisis. Vaccination is a proven, specific preventive measure. The federal government should endorse voluntary vaccination and allow people to make their own decisions as to risk.
An infected terrorist is likely to have no visible disease, to feel well enough to travel, and to transmit disease actively to others. As the prodromal fever drops, the smallpox rash is not visible inside the mouth. The terrorist temporarily feels better and is very infectious. The rash becomes obvious several days later.2 A plausible scenario is that of terrorists traveling to multiple cities and disseminating smallpox in subways and airports, resulting in hundreds of thousands to millions of cases. Multiple releases from an aerosol container would be far worse.
Ring vaccination in the eradication program worked relatively slowly, was applied to populations with high levels of immunity and less mobility than Americans have today, and was applied in situations where there was no malicious intent. Kaplan et al., in a quantitative comparison of ring vaccination and immediate postattack mass vaccination, demonstrate that a moderate attack would overwhelm ring vaccination, even when the supply of vaccine is plentiful.3
The jurisdictional and management lessons of Dark Winter remain valid. Outbreaks in Yugoslavia and elsewhere teach us that one case can lead to the infection of many others. With malicious dissemination, particularly in the first round of infection, we must expect rates of spread that are substantially higher than 1 terrorist to 10 victims. Subsequent rounds are likely to have lower rates of spread.
J. Donald Millar, a former director of the smallpox-eradication program of the Centers for Disease Control and Prevention, has made the following statement: "The idea that the government would withhold the only effective means of protecting the population from a terrible disease until an epidemic is confirmed is new to public health. Prevention, in this new concept, obviously has no meaning for the `sentinel' Americans who will become ill and die of smallpox as trigger for the government's response. That is not good public health, and is certainly not good protection from bioterrorism."4 Selective, step-by-step, voluntary preexposure vaccination is a low-risk, high-benefit approach that would make any postexposure strategy easier.
William J. Bicknell, M.D., M.P.H.
Boston University School of Public Health
Boston, MA 02118-2526
wbicknel{at}bu.edu
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