ATLANTA — Smallpox shots may have triggered a painful heart inflammation in a very small number of emergency workers vaccinated after Sept. 11, 2001, researchers say.
A study in today's Journal of the American Medical Association showed a higher rate of heart-inflammation cases than ever documented before in people who got smallpox vaccinations.
"I think that was completely not anticipated," said Dr. Inger Damon, an author of the study.
Overall, however, the vaccine appears to carry an extremely small risk of serious side effects, researchers reported after looking at nearly 700,000 civilians and soldiers who received vaccinations after the terror attacks.
The United States ended routine childhood vaccination against smallpox in 1971, and the World Health Organization reported the disease was eradicated in 1980. But about 15 months after the Sept. 11 attacks, the U.S. government ordered certain military personnel vaccinated and recommended shots for front-line health-care workers.
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The smallpox vaccine, Dryvax, made by Wyeth, has long been suspected of triggering neurological complications, including encephalitis, in rare cases. But Dryvax was not associated with heart problems until 2003, when three adults died suddenly of heart attacks. As a precaution, health officials advised people with heart disease to skip the vaccination.
One of the studies published today looked at emergency responders, a group made up largely of female health-care workers ages 40 to 64.
Researchers counted 100 possible cases of serious side effects in 37,901 people who got the shots from January to October 2003. Among the 100 were 21 cases of nonfatal heart inflammation and six heart attacks, two of which were fatal.
Researchers said they could not tell if the heart attacks were caused by the vaccine. They said the number of heart attacks was not out of line with what would be expected in a patient population of that size and age range.
But the rates of inflammation were higher than those seen in previous studies. Further research may help determine whether these cases were triggered by the vaccine, said Damon, chief of the poxvirus program at the Atlanta-based federal Centers for Disease Control and Prevention.
