A press-released claim that the smallpox vaccine could increase immunity to HIV has boosted share prices of the vaccine's manufacturers — but has been met with hostile scepticism by the scientific community.

The claim, made by researchers at George Mason University in Fairfax, Virginia, on 11 September, has not been substantiated by published data. Other scientists are particularly annoyed at the unconventional method of the announcement, because of the claim's potential implications for past and future smallpox-vaccination programmes.

Raymond Weinstein, a researcher at George Mason's National Center for Biodefense, who led the research, says he noticed that the countries where smallpox had been eradicated first now have the highest rates of HIV infection. Together with Ken Alibek, a former Soviet bioweapons scientist who is now at George Mason, he directed a study by microbiologists at George Washington University Medical Center in Washington DC. Blood was tested from ten volunteers who had been vaccinated against smallpox, and ten who had not. The team claims that blood cells from vaccinated subjects became infected with four times less HIV than cells from unvaccinated subjects. Smallpox and HIV can both use the same cell-surface protein to infect cells, so it is plausible that there may be a link between immunity to the two diseases, claims Weinstein.

Weinstein says that the team then briefed officials at the National Institutes of Health and its parent agency, the Department of Health and Human Services. They decided to announce their findings in a press release, he says, because federal scientists warned them that they might try to race a study of their own into publication.

But Ed Tramont, director of the Division of AIDS at the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, says that he is not aware of any scientists working on duplicating the results. And he cautions against overinterpreting the press-released data. Many vaccinations cause temporary boosts in immunity soon after patients receive them, he says, and many adults who received the smallpox vaccine as children have subsequently contracted HIV.

Donald Henderson, a major architect of the smallpox-eradication plan and an adviser to the federal government on bioterrorism preparedness, says that there is in any case no consistent relationship between smallpox eradication and HIV emergence in Africa. “It doesn't make a lot of sense,” he says.

But on the day that Weinstein and Alibek made their announcement, shares in smallpox-vaccine manufacturer Acambis jumped by 10% to a new high. And even though vaccine-maker VaxGen had announced earlier this year that its experimental HIV vaccine failed in clinical trials, its shares also rose by 10%.