Laboratory trials suggested that immunity to smallpox triggered by the smallpox vaccine can inhibit the replication of the AIDS virus, the researchers said in the journal BMC Immunology.

Vaccinations against smallpox could have kept HIV transmission partially under control in the early days of the outbreak, which is thought to have begun in the 1950s.

Starting in the early 1960s  the  withdrawal of the smallpox vaccine, called vaccinia, starting at about the same time might have freed HIV to spread unfettered, the researchers said.

The results are preliminary and it is “far too soon to recommend the general use of vaccine immunization for fighting HIV,” said one of the researchers, Raymond S. Weinstein of the biodefense program at George Mason University’s Prince William campus in Manassas.