BBC News on line (May 17, 2010)
The worldwide eradication of smallpox may, inadvertently, have helped spread HIV infection, scientists believe.
Experts say the vaccine used to wipe out smallpox offered some protection against the AIDS virus and, now it is no longer used, HIV has flourished.
The US investigators said trials indicated the smallpox vaccination interferes with how well HIV multiplies. But they say it is too early to recommend smallpox vaccine for fighting HIV.
Lead researcher Dr Raymond Weinstein, from Virginia's George Mason University, said: "There have been several proposed explanations for the rapid spread of HIV in Africa, including wars, the reuse of unsterilized needles and the contamination of early batches of polio vaccine.
"However, all of these have been either disproved or do not sufficiently explain the behavior of the HIV pandemic."
Dr Weinstein and his colleagues believe immunization against smallpox may go some way to explain the recent rises in HIV prevalence.
Smallpox immunization was gradually withdrawn from the 1950s to the 1970s, following the worldwide eradication of the disease, and HIV has been spreading exponentially since then, they say.
Now, only scientists and medical professionals working with smallpox are vaccinated.
To test if the events may be linked, the researchers looked at the white blood cells taken from people recently immunized against smallpox and tested how they responded to HIV.
They found significantly lower replication rates of HIV in blood cells from vaccinated individuals, compared with those from unvaccinated controls.
The smallpox vaccine appeared to cut HIV replication five-fold.
The researchers believe vaccination may offer some protection against HIV by producing long-term alterations in the immune system, possibly including the expression of a receptor called CCR5 on the surface of white blood cells, which is exploited by the smallpox virus and HIV.
Significantly reduced CCR5-tropic HIV-1 replication in vitro in cells from subjects
previously immunized with Vaccinia Virus
Raymond S. Weinstein, Michael M. Weinstein, Kenneth Alibek, Michael I. Bukrinsky, and Beda Brichacek
BMC Immunology (to be published)