Clinical trials on the gel microbicide, Carraguard, have shown it does not prevent HIV infection.

University of KwaZulu Natal researcher, Jerry Huswein Coovadia, says: "If people thought that a vaccine was around the corner ... they (have) had to rethink that, and the same applies to microbicides. But even that is not enough; you do have to have social change, which means that people themselves must change.

Coovadia says this failure is but one is a series of blows - similar to a failed trial in 2007 - and that perhaps this is an opportunity to rethink the virus and its vaccine and also in the manner in which researchers are tackling the epidemic.

Coovadia says science alone could not provide answers and that many countries, including those in Africa had made strides in controlling the epidemic by changing its social and sexual behaviour.

HIV is a pandemic, with an estimated 33.2 million people now living with the disease worldwide. As of January 2006, the Joint United Nations Programme on HIV/Aids (UNAIDS) and the World Health Organisation (WHO) estimate that Aids has killed more than 25 million people since it was first discovered on June 5, 1981.