Diluted smallpox vaccine effective in young adults. (Use of Old Vaccine Stockpiles).

SAN DIEGO -- Stored supplies of smallpox vaccine appear to confer immunity on previously unvaccinated young adults, even in dilute form, but some recipients develop moderately severe influenzalike reactions, one of the vaccine's investigators reported at a meeting sponsored by the Los Angeles Pediatric Society.

"The vaccine we have works," concluded Dr. Kathryn M. Edwards, professor of pediatrics and vice chair for clinical research at Vanderbilt University in Nashville.

Trials of historic vaccine sequestered by the Centers for Disease Control and Prevention and stockpiles discovered in storage by Aventis Pasteur "both look to be highly infective still. It appears both of these vaccines can be diluted at least 1:5 and maybe 1:10 and still achieve very vigorous takes."

This suggests there would be enough smallpox vaccine to immunize the entire U.S. population.

Among the 60 persons aged 18-35 years immunized at her site, just 2 did not have a "take," she said. Because the investigation has not yet been unblinded, Dr. Edwards does not know which dilution of vaccine those individuals received. To see how thinly vaccine stores could be stretched, some people received doses diluted more than 30 times.

In the event that large numbers of people would need smallpox vaccination, Dr. Edwards' experience suggests there may be widespread influenzalike reactions to the vaccine. "A fair number of adults have very high fevers: 103[degrees], 104[degrees], 105[degrees] F."

About one in three subjects missed a day or more of work due to illness following vaccination, peaking at about 10 days after vaccination.