Researchers to test smallpox vaccine

Smallpox is a highly contagious viral disease that proves fatal to about 30 percent of its victims. Routine vaccination was stopped in the United States in 1971, and smallpox was declared eradicated worldwide in 1980. Ever since last fall’s anthrax attacks on the East Coast, however, smallpox has been considered a likely candidate for use in biowarfare, and there has been strong interest in determining how the United States could best protect its population in case of a smallpox attack.

Researchers hypothesize that a diluted dose of the smallpox vaccine may be enough to protect previously vaccinated individuals – including most Americans over age 30. If this hypothesis were confirmed, the United States’ limited existing supply of the vaccine could be stretched further. The smallpox vaccine is no longer manufactured, but a supply is kept by the federal Centers for Disease Control and Prevention.

“The key questions we’re studying are, does the smallpox vaccine we have from 30 years ago still produce a protective response in people who have already received the vaccine, and can we dilute it to make a greater supply available to the U.S. population?” asked Cornelia Dekker, MD, associate professor of pediatrics at the Stanford School of Medicine and the medical director of the Stanford-Lucile Packard Children’s Hospital Vaccine Program. “The idea is that the more we can safely dilute this vaccine and still have it be effective, the more doses we can have available if we need them.”

Stanford has formed a partnership with Kaiser in the randomized, double-blind study, which is funded by a grant from the National Institutes of Health. “In light of increasing concerns about vaccinating as many people as possible against a bioterrorist attack, I’m glad we’re able to learn how effective these decades-old vaccines still are,” said Steve Black, MD, co-director of the Vaccine Study Center at Kaiser.

To test whether diluted doses can produce an effective immune response in previously vaccinated individuals, approximately 90 volunteers between the ages of 32 and 70 will be enrolled at Stanford, and roughly another 100 at Kaiser Permanente. Volunteers will be randomly assigned to one of three groups. One group will receive a full-strength dose of the vaccine. A second group will receive a dose that has been diluted five times, and a third group will receive a dose that has been diluted 10 times. A total of 970 volunteers will participate in this study at nine study sites across the nation.

All participants will be carefully monitored immediately following vaccination and will return to the medical center for at least eight clinic visits over the
next two months. In addition to determining the effectiveness of diluted doses, the study will give scientists other valuable information. It will help monitor the safety of
the smallpox vaccine. It will help scientists understand how long the immunity from a previous vaccination lasts. And, significantly, it may help advance efforts now under way to develop a better smallpox vaccine with fewer side effects. “The way we understand immunity today is much more advanced than it was in the 1970s,” Dekker said.