In conjunction with the U.S. government, hospitals across the country are recruiting 900 people to undergo testing to see how much vaccine is needed to protect them from smallpox.
Unlike other subjects currently undergoing vaccine tests, these men and women will all have been vaccinated against smallpox decades ago. Doctors suspect the previous vaccinations have worn off but may still prevent these people from needing full doses.
"We already know what an optimal dose is. We're asking what we can get away with," says Dr. Steven Black, co-director of the Kaiser Permanente Vaccine Study Center in Oakland, Calif. The center's vaccine tests are scheduled to begin today.
At issue is the country's ability to stretch its limited supply of smallpox vaccine. Researchers hope they can multiply the number of available doses by making them smaller. One dose, for example, could be divided into five or 10 doses.
While health officials hope to buy doses of new vaccine, Aventis Pasteur is donating 70 million doses to the government. The doses had been in storage for decades.
Officials say the doses can act as an insurance policy in case a smallpox attack comes before the new doses are ready. During the summer, several laboratories began testing the doses in 350 people between the ages of 18 and 32 who were never vaccinated before.
In the new study, Kaiser Permanente will enroll 90 people. All the subjects must be at least 32 years old -- born before smallpox vaccination was ceased in the United States -- and younger than 70.
Officials will also check to make sure the subjects were actually vaccinated for smallpox. Most will still have a scar on their upper arm, although it may have faded away and be difficult to see without close examination, says Dr. Cornelia Dekker, an associate professor of infectious diseases at the Stanford University School of Medicine, which is also taking part in the national study.
"Sometimes you have to look real hard" for a scar, Dekker says. "The longer it is since vaccination, the more the skin seems to smooth over and heal."
If a scar isn't visible, subjects will have to bring in written proof that they were vaccinated, she says.
The subjects will be inoculated with smallpox vaccine from the Aventis Pasteur supply or the so-called Dryvax vaccine. During the vaccination, nurses will poke their arms 15 times. "That puts [the vaccine] into the layers of skin, so it can grow, replicate and stimulate the immune system," Dekker says.
The subjects, who will be paid, will return for five doctor's visits during the first two weeks after the vaccination, Dekker says. Researchers will examine their arms for signs their bodies are reacting to the vaccines.
For a smallpox vaccine to be effective, the body's immune system must prime itself against the virus in the vaccine, a much milder variation on smallpox. It's possible that the immune systems of the subjects may still have leftover protection from their decades-old vaccinations, preventing the process from going far enough to create lasting protection, Black says.
"It's a race between the immune system and the virus on their shoulder. The immune system might win and they wouldn't get a 'take,'" Black said. In that case, they would need larger doses.
Officials expect results from their study within six months.
The smallpox vaccine isn't harmless. An estimated one in 1 million people will die after being vaccinated. A commentary in today's issue of the Journal of the American Medical Association suggests there may be another very small risk -- the possibility that vaccinated people will transfer the virus caused by vaccination to unvaccinated people. That could result in severe skin rashes.
The U.S. Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices is meeting today and tomorrow to discuss the risks of vaccination and other smallpox vaccine issues.
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