Smallpox protection has lapsed, scientist says

Study of lab workers casts doubt on old vaccinations

May 31, 2002|By Jonathan Bor | Jonathan Bor,SUN STAFF

Adults who were vaccinated against smallpox before the U.S. government halted routine vaccinations 30 years ago are unlikely to carry any immunity against the disease, a Rockville scientist has reported.

The study questions the widely held belief that significant numbers of people who were previously vaccinated remain immune from smallpox for up to 50 years.

Dr. Michael Sauri said his findings suggest that mass vaccinations would be necessary in the event that a terrorist unleashed smallpox. The study, which involves 320 laboratory workers, appears in the spring issue of Maryland Medicine, the journal of the state medical society.

Government officials have favored a more limited strategy of "ring vaccination," in which health workers vaccinate people who have come into contact with the sick plus those living within a confined geographical area.

"I don't think the ring vaccination strategy is going to work," said Sauri, director of Occupational Health Consultants, a private clinic in Rockville. "You may as well go to mass vaccination."

Though routine vaccinations in the United States were halted in 1972, some laboratory workers who work with the vaccinia virus - the agent used to manufacture smallpox vaccine - have continued to get immunized.

The Rockville clinic vaccinates lab workers who have been using the virus to develop vaccines against the AIDS virus and other deadly infections.

After last fall's anthrax attacks raised fears that a bioterrorist could unleash far deadlier smallpox, Sauri decided to review records of lab workers who had been vaccinated between 1994 and 2001 and had also been immunized as children.

Fewer than 10 percent of the 320 scientists experienced skin reactions that indicated they still harbored sufficient immunity to protect them from smallpox if they were ever exposed.

People with robust immunity develop a relatively small scab, in contrast to those with poor immunity who get a larger and longer-lasting scab.

Today, about 60 percent of the U.S. population (about 168 million people) is old enough to have been vaccinated against the disease as children.

But Sauri said the number who remain immune is probably smaller than the study suggests, taking into account the large number of people suffering from AIDS, cancer and other diseases that hinder their ability to fight off infections.

Dr. Robert Edelman, a vaccine researcher at the University of Maryland School of Medicine, said the study presents "disturbing evidence" that experts might have overestimated the degree of protection that exists among the U.S. population.

But Edelman said he had not yet read the study and would need to analyze its methods before reaching any conclusions. "To say that there is not likely to be immunity as a result of old immunization is a statement that has got to be backed up with very strong facts," Edelman said.

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