1901-03 Smallpox Epidemic Offers Lessons

Boston Outbreak Shows Smallpox Vaccination Provides Benefits Even After Infection

Dec. 18, 2002 -- Few doctors today have ever seen a case of smallpox, but the lessons learned from a smallpox epidemic a century ago in Boston may provide some valuable and perhaps even reassuring lessons for both physicians and the public. During that epidemic, a total of 1,596 cases and 270 deaths were reported.

A new review of the 1901-03 outbreak shows that previous vaccination against the disease not only lessened the likelihood of serious infection, but vaccination after the epidemic began improved the chances of survival of those who got sick.

Smallpox was eradicated worldwide in 1977, but the threat of terrorists using the virus as a biological weapon has renewed interest in the disease. Last week, President Bush announced that the government would release some of its vaccine stockpiles and begin vaccinating medical and military personnel in 2003, with widespread vaccination among the public to start in 2004.

Although researchers say more than 95% of the smallpox cases reported in the 20th century were caused by a mild form of the variola virus (smallpox) called variola minor, the Boston epidemic was caused by a more dangerous form of the virus known as variola major. The two types of the virus cause similar symptoms, but the minor form rarely causes serious illness or death.

In a study published in the Dec. 17 issue of the Annals of Internal Medicine, researchers looked at the clinical records of 243 patients who were admitted with smallpox to a Boston hospital during the epidemic and examined what factors seemed to increase the patients' chances of survival.

Of the 206 patients for which survival information was available, 17.5% (36) died. Researchers found that 79% of the deaths occurred seven to 14 days after symptoms began and all deaths occurred within 18 days of symptom onset.

Early symptoms such as fever, headache, and backache usually begin one to two weeks after infection and are followed by the eruption of lesions on the face and extremities.

The study also found children under 5 and adults over 45 were less likely to survive smallpox, but survival was not significantly affected by the sex, race, or birthplace of the victim.

When the outbreak began in 1901, records show that most residents were not vaccinated against smallpox, and 485,000 vaccinations were administered by the end of the year. Researchers say patients with a history of vaccination were more likely to develop a milder form of the disease and were more likely to survive than those who were never vaccinated.

In addition, patients who had no history of vaccination, but were vaccinated within three weeks of hospitalization for smallpox also had a better chance at survival than those who had never been vaccinated.

"Because the [type of smallpox virus used in the vaccine] inoculated into the arm has a shorter incubation period (six to eight days) than variola virus acquired through respiratory inhalation, vaccination can alleviate or even abort smallpox if given soon after exposure," write researcher Joel G. Breman, MD, DTPH, of the National Institutes of Health, and colleagues.

Researchers say those findings are especially promising because it shows vaccination after a possible bioterrorist attack would still likely provide significant benefits to many.

Also, they say doctors today have many advantages in managing a smallpox epidemic than they did a century ago, such as advances in the treatment of both the disease itself and secondary infections, better regulated vaccine production and quality, and greater federal support.