Diluted Smallpox Vaccine Just As Effective, Study Shows

June 18, 2003

            Diluted vaccine to prevent smallpox is just as effective as a full dose in provoking the body’s defenses to fight off the virus, according to a study to be published in the April 25 issue of the New England Journal of Medicine. The journal is announcing the results nearly a month ahead of schedule because of the public health implications of the findings.

            The vaccine was effective in nearly all 680 people who were vaccinated, says John Treanor, M.D., associate professor and director of the Vaccine and Treatment Evaluation Unit at the University of Rochester Medical Center, one of four sites that conducted the study last fall. The vaccine was effective in all 170 people vaccinated in Rochester as part of the study funded by the National Institute of Allergy and Infectious Disease.

The results mean that, in case of a bioterrorism threat and a vaccine shortage, existing stocks of the vaccine could be stretched to inoculate at least five times as many people as originally intended, according to Tommy G. Thompson, secretary of the U.S. Department of Health and Human Services.

            One surprise to doctors and nurses was the extent of the side effects, which usually involved flu-like symptoms, redness around the site of injection, a sore arm, or a rash.

            “No one doing the study had ever vaccinated anyone against smallpox, and we were all a little surprised by the side effects,” says Treanor. “But once we talked to some older physicians who did such vaccinations routinely decades ago, it became clear that this isn’t any different from what would be expected when vaccinating a large group of people against smallpox for the first time.”

            Since Rochester is one of four sites nationwide that took part in the initial study, the region offers a unique opportunity to learn more about smallpox and the immune system. Researchers are currently weighing several new studies to learn how the body responds to the smallpox vaccine.

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