But does the presumed danger of smallpox justify the risks and costs of vaccination? It’s hard to tell. Because smallpox was eradicated, we can learn about its dangers only from history. But history seldom tells us as much as we want to know.
Estimates of mortality from smallpox differ. The most widely cited authorities, including the Centers for Disease Control and Prevention, assert that smallpox can kill up to a third of its victims. But past epidemics varied enormously, ranging from only a few deaths to far higher proportions of those stricken.
Before the 1700s, European smallpox epidemics seem to have been comparatively mild, with minimal death rates. But thereafter that earlier form of the disease may have been displaced by a more lethal strain. Smallpox became more severe in Europe during the next two centuries.
The quest for ways to prevent or treat it led to the development of inoculation — the use of the smallpox virus to induce a mild infection — early in the eighteenth century. In the American colonies, the introduction of inoculation in 1721 set off a fierce debate about whether it would save lives. The quarrel was so fierce that a bomb was thrown into the house of a leading advocate of inoculation, the Puritan minister and historian Cotton Mather. The bomb failed to explode.
The controversy led doctors to collect more accurate and detailed information about fatalities. They found death rates to be about 15 percent. The great epidemic in Boston in 1721 sickened slightly more than half of the 11,000 residents and killed 14 percent of those infected.
Epidemics elsewhere, even after the development of inoculation, could be more severe. An epidemic in Sheffield, England, in 1887 and 1888 killed just under half its 552 victims. Scattered accounts of fatalities among non-Europeans hinted at even worse severity.Ý An epidemic among the Griqua nation in South Africa in 1831 was reported to have caused mortality rates of 80 percent. We now estimate that epidemics among the native peoples of North and South America killed about 90 percent of victims.
Even twentieth-century epidemics could be terrible. From 1933 to 1938, among 60,000 reported cases in the Punjab in Western India (now Pakistan) 47 percent died. As recently as 1972, an epidemic broke out in a refugee camp in West Bengal. All infected patients were hospitalized, and nearly half the 764 patients died. Similarly, of 79 unvaccinated patients who became ill from smallpox in Europe and Canada between 1950 and 1971, 52 percent died.
Nor, over the centuries, was death the only reason to fear smallpox. It could cause disfigurement, sterility, miscarriage and blindness. More than half of the survivors had permanent scars. To the millions of people it has killed, we must add those whose lives it has ruined.
Assuming that terrorists were to develop a virulent strain of smallpox, we would have no reliable way to forecast its impact. We don’t know how whether childhood vaccinations would still protect older Americans. A new strain might even prove so virulent that its effectiveness as a weapon would be defeated: quickly prostrated victims might be less likely to spread the disease to others.
In deciding about vaccination, Americans will surely want to know about the substantial risks of permanent impairment, not just the odds that they might die. They would also want to know about the much lesser risks of vaccination itself. As the Bush program indicates, modern vaccination is relatively safe for the healthy, but it is not permanent. To remain completely protected, each person would need revaccination every few years.
A secondary danger is that vaccinated people can spread the disease to others. In Sweden in 1963, five vaccinated persons who were exposed to a smallpox patient spread the disease to others without becoming ill themselves. Between 1959 and 1973, people with good vaccination records carried smallpox back into Europe about ten times, causing nearly one third of all outbreaks.
If health workers are the first to be vaccinated, as planned, they might spread smallpox from hospitals into the unprotected community. Moreover, widespread vaccination in the United States could contain any contagion here but would not keep people in other countries safe; travelers who seemed to be healthy could spread the disease around the world.
In initiating vaccinations, the administration has decided that the threat of smallpox is real, but any estimate of the mortality and suffering an outbreak might cause is just a guess. History tells us only that the extent of that threat is unpredictable. Let’s hope this demon remains safely buried in the past.