Scientists have come up with what they claim to be conclusive evidence that undermines claims that the contamination of experimental polio vaccines caused HIV — the virus responsible for AIDS – to jump from chimpanzees into humans.

The allegations received widespread publicity in 1999 in a book published by a US journalist, Edward Hooper, based on several years' investigation.

A study published in this week's Nature shows that chimpanzees in the Democratic Republic of Congo — where the contamination is alleged by Hooper to have occurred — do indeed carry simian immunodeficiency virus (SIV).

But the strain of the virus that they carry is very different, in evolutionary terms, from all strains of HIV-1, providing direct evidence that these chimpanzees were not the source of the human AIDS pandemic.

Most HIV/AIDS researchers believe that the virus that causes AIDS originated in chimpanzees and jumped into humans in the 1930s on exposure to primate blood through hunting and preparing meat.

Speculation has, however, continued that HIV crossed into humans as a result of contamination of the oral polio vaccine. This theory claims that the virus was transmitted to humans when chimpanzee tissues were used in the preparation of the vaccine.

Link to study in Nature