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WEDNESDAY, March 10 (HealthDayNews) -- Armed with new results from research in monkeys, scientists say they've moved a step closer toward developing an alternative for the millions of people who can't take the smallpox vaccine.

A weakened version of the vaccine appeared to protect monkeys from the simian equivalent of smallpox, the scientists report. This raises the possibility that the alternate vaccine could protect humans on its own, or at least prepare their bodies to fight off any bad effects of the traditional vaccine.

Ultimately, the development of an alternate vaccine may deter terrorists by robbing them of a way to threaten people, says study co-author Dr. Bernard Moss, who researches viral diseases at the National Institute of Allergy and Infectious Diseases. "The hope is that if we have good preventatives, we'll never have to use them because smallpox will not be used as a bioweapon if our defenses are very good."

Ideally, people who get smallpox vaccinations develop an infection in their arm from vaccinia, a virus related to smallpox. Their bodies beat back the infection and are then primed to tackle the smallpox virus.

But doctors fear the vaccine will sicken or even kill many people whose bodies can't properly fight off the infection. Since routine smallpox vaccinations ceased in the 1970s, the number of people with compromised immune systems has grown. They include AIDS patients, who are living longer thanks to powerful drugs, and recipients of organ transplants.

People who have suffered from eczema or other skin infections are also at risk, along with pregnant women.

No one knows exactly how many people shouldn't receive smallpox vaccinations, but experts put the number at perhaps 20 million in the United States. The number includes the roommates, spouses and children of those who are susceptible to problems. Since the vaccine causes a potentially contagious infection, those people could infect those close to them.

As the risk of a terrorist attack involving smallpox has grown, researchers have been trying to both understand the dangers of the existing vaccine and create alternatives. In the new study, researchers vaccinated 18 monkeys with a weakened vaccinia virus that was developed in the 1960s. "It was considered faster to do this than to make a totally new vaccine," Moss says.

The vaccinations, some given in conjunction with the traditional vaccine, protected the monkeys against monkeypox. Six other monkeys that didn't receive vaccinations got sick or died when exposed to the disease.

The results of the study appear in the March 11 issue of Nature. In another study, Moss and his colleagues found the alternative vaccine didn't hurt mice whose immune systems had been weakened. Those findings will appear in the early March 11 online edition of the Proceedings of the National Academy of Sciences.

The next step will be to test the alternative vaccine in humans. Since it's unethical to try to infect people with smallpox, researchers will focus on the safety of the vaccine and its effects on the immune system, Moss says. Researchers will also want to know if the alternative approach works best as a kind of "pre-vaccine" before a traditional vaccination.

However, one expert says the future is not entirely bright. If the alternative vaccine must be given along with the traditional vaccine, the combination could spell trouble if health-care workers make mistakes during the vaccination procedures, says Dr. Steven Black, co-director of the Kaiser Permanente Vaccine Study Center. And the combo would still leave recipients at risk of infecting others in their households, he says.

"It's a step in the right direction, but it's not a major advance," Black says.

In other smallpox-related news, the U.S. Food and Drug Administration on Monday announced it has issued guidelines for the development of drugs to treat the side effects of the smallpox vaccine, which can range from minor skin irritation to serious medical problems.

More information

For a history of the smallpox vaccine, check out Stanford University or the U.S. Centers for Disease Control and Prevention. For more on bioterrorism and what officials are trying to do to stop it, visit the National Memorial Institute for the Prevention of Terrorism.

(SOURCES: Bernard Moss, M.D., Ph.D., chief, laboratory of viral diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Md.; Steven Black, M.D., co-director, Kaiser Permanente Vaccine Study Center, Oakland, Calif.; March 11, 2004, Nature; March 11, 2004, Proceedings of the National Academy of Sciences online)

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