A controversial theory that a vaccine sparked the HIV epidemic was cast further into doubt by Oxford scientists.
The theory argues that the Aids virus was initially transmitted to humans in the late 1950s through an oral polio vaccine grown in chimpanzees. It is claimed that an ape version of the virus contaminated the vaccine and introduced HIV. Supporters of the theory point to the fact that clusters of HIV subtypes seemed to have appeared at the same time.
They say this suggests that multiple viruses were simultaneously transferred from chimps to humans via the vaccine.
But today the theory was challenged by Oxford University researchers studying the genetic diversity of HIV in the Congo, the most likely point of origin for the virus.
They found the Congo strains had sufficient variation to have produced all the different types of HIV.
Dr Eddie Holmes, from Oxford's Department of Zoology, said: "Our results certainly make the polio vaccination theory far less likely."
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