Ten years after the former US president Bill Clinton predicted the arrival of a vaccine for AIDS within a decade, one of the world's leading HIV researchers has admitted he is pessimistic about the prospects of achieving an effective vaccine in the near future.

At a briefing in London last week of the International AIDS Vaccine Initiative, Robin Weiss of University College London said that the enormous variation among HIV viruses was continuing to prove a huge stumbling block.

“I'm the pessimistic person on the panel,” Professor Weiss said, noting that there were as many or more genetic variants of HIV in the body of one infected person as there were different …