Vaccinations for smallpox that were phased out during the 1950s, 1960s and 1970s, as the disease was eradicated, could have helped to slow the spread of HIV and Aids, experts have discovered.
Tests show the vaccine appears to have a well-developed ability to inhibit the Aids virus, which could have given protection to people in the early days of the HIV epidemic.
But ending the smallpox vaccination programme may have contributed to the explosive spread of HIV/Aids that followed in the 1980s and beyond, with rates of HIV infection increasing exponentially around the world since that time.
Scientists in the US studied white blood cells taken from people recently immunised with the smallpox vaccine, vaccinia.
They found that immunisation led to a five-fold reduction in the ability of HIV to replicate in the cells.
Dr Raymond Weinstein, from George Mason University in Mannasas, Virginia, US, said: "There have been several proposed explanations for the rapid spread of HIV in Africa, including wars, the reuse of unsterilised needles and the contamination of early batches of polio vaccine. However, all of these have been either disproved or do not sufficiently explain the behaviour of the HIV pandemic.
"Our finding that prior immunisation with vaccinia virus may provide an individual with some degree of protection to subsequent HIV infection suggests that the withdrawal of such vaccination may be a partial explanation."
The research was published in the journal BMC Immunology.
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