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Smallpox Vaccine Find May Halt Need for Dilution

Millions of doses found, but thinning out existing one works

THURSDAY, March 28, 2002 (HealthDayNews) -- The surprise discovery of a drug company's huge -- and apparently forgotten -- cache of smallpox vaccine might well obviate the need for a major thinning-out of America's inadequate stock.

The French pharmaceutical firm Aventis Pasteur stumbled on between 70 million and 90 million doses of smallpox vaccine in the company's freezers, according to a report today in the Washington Post. If these doses are proven effective, the cache means that even thinning one-to-four would safely cover every American.

The news came the same day a new study showed that a limited supply of the vaccine can be safely diluted by a factor of five and even 10 without sacrificing its ability to protect against the deadly virus.

Len Lavenda, a spokesman for Aventis' Swiftwater, Pa.-based U.S. operations, said the government asked the company not to discuss the newfound vaccine in the "interest of national security." Health and Human Services Secretary Tommy Thompson has scheduled a press conference tomorrow to discuss the discovery, Lavenda said.

Bill Hall, an HHS spokesman, would not confirm the number of doses found at the company. "We have been in discussions with Aventis about the efficacy of their vaccine," he said. "Those discussions are still ongoing, but we believe they are nearing conclusion."

Hall said the government and the drug firm were trying to iron out various "legal" issues, but he would not be more specific.

The government currently has access to 15.4 million doses of the old "Dryvax" vaccine, made by Wyeth Laboratories of Marietta, Pa. These were kept as a precaution after production stopped in 1982. In the wake of the anthrax attacks last fall, health officials proposed thinning out this stock to allow as many as 150 million Americans to be immunized against the infection if terrorists launched an assault with the virus.

What's more, the government has also contracted with another biotech company, Acambis Inc., to buy an additional 209 million doses of smallpox vaccine by the end of this year. That would raise the stockpile to 286 million doses (assuming a one-to-five dilution of the 15.4 million Dryvax doses alone), not including the new cache from Aventis.

According to the Post, the Aventis and Wyeth vaccines are essentially identical, except that the Aventis version is in frozen liquid form. (The Wyeth vaccine is freeze-dried.)

Meanwhile, in the new, nationwide, multi-center study that was released today, scientists at Saint Louis University tested the various doses of the vaccine on 680 people who had not been previously vaccinated. The volunteers were randomly assigned to receive a one-to-10 dilution, a one-to-five formula, or a full-strength vaccine. The team found that all strengths of the vaccine, which was at least 20 years old, generated signs of protection from smallpox in at least 97 percent of the cases.

A smaller study, of only 60 people, found that the vaccine weakened as it thinned. But the researchers said that trial used vaccine with about a third the number of virus particles as that used in the larger study.

"What's important isn't the dilution, it's the amount of virus in the starting material. If you dilute it one-to-10 it works just great," said Dr. Robert Belshe, a Saint Louis University immune specialist who helped conduct both government-funded studies.

A report on the research appears this week in an early edition of the April 25 issue of the New England Journal of Medicine devoted to smallpox.

"The public health implications of [the findings] are enormously important," Secretary Thompson said in a statement released today. "We now know that in the unlikely event of an intentional release of smallpox, our stockpile of smallpox vaccine can be expanded fivefold as we had planned. The success of this study puts us one step closer to our goal of having enough vaccine for every American if needed to respond to a potential outbreak."

Smallpox vaccine isn't administered by injection, but rather is delivered with a miniature pitchfork dipped in the substance and then scratched into the skin. If an ulcerous blister appears, it is considered a sign of a successful "take." The immunization, which is given 15 times per person, uses live vaccinia virus, a relative of cowpox and possibly a now-extinct form of horse pox, Belshe said.

Belshe and his colleagues found that skin takes mirror a systemic immune response to the smallpox virus, which is known as variola. "That's very good evidence that if you have a take you are protected," Belshe said. "It does not tell us how long protection lasts, but evidence suggests it lasts a long, long time."

The study was not conducted on people who have already been vaccinated against smallpox. About half of Americans have been vaccinated; routine immunization stopped in 1972, when officials felt the risk of contracting the disease was nearly nonexistent. The researchers are now looking into whether and in whom booster vaccinations are necessary.

The Centers for Disease Control and Prevention has advocated "ring" vaccination to contain smallpox in the event of a bioterrorism attack with the virus. This approach calls for tracking initial cases and immunizing successively widening circles of their contacts at risk of infection.

But in one of several editorials accompanying the journal articles, Dr. William Bicknell, a public health expert at Boston University, argues for voluntary mass inoculations before any attack occurs.

"The CDC's position is seriously flawed, and containment will lead to huge numbers of preventable deaths," Bicknell said in an interview with HealthDay.

Based on past experience with smallpox immunization, 180 people would die from adverse reactions to the vaccine in a voluntary mass inoculation effort -- as many as die in traffic accidents every 1.5 days, he said. Although not everyone who received the vaccine would be fully protected, waiting to vaccinate until cases crop up would lead to hundreds of thousands, if not millions, of deaths as officials scramble to contain the infection, Bicknell said.

"You will know there's been an attack after it's too late for the vaccine to help you," he said. Voluntary preemptive vaccination might discourage an attack with smallpox, Bicknell added. It could also protect other countries by preventing "leakage" of the virus through international travel.

What To Do

Smallpox vaccine isn't for everybody. People with compromised immune systems, such as AIDS and cancer patients, as well as those with the skin condition eczema, can have fatal reactions to the inoculations.

For a history of the smallpox vaccine, check out Stanford University.

For more on bioterrorism and what officials are trying to do to stop it, try the National Memorial Institute for the Prevention of Terrorism or the Centers for Disease Control and Prevention.

SOURCES: Robert Belshe, M.D., professor, Saint Louis University School of Medicine, St. Louis; William Bicknell, M.D., M.P.H., professor of public health, Boston University School of Public Health; Len Lavenda, spokesman, Aventis Pasteur, Swiftwater, Pa.; Bill Hall, spokesman, U.S. Department of Health and Human Services, Washington, D.C.; Statement from Tommy Thompson, Secretary of Health and Human Services; April 25, 2002 New England Journal of Medicine; March 28, 2002 Washington Post
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