The software tycoon, Bill Gates, has announced that his charitable foundation will donate $100m (£71.5m) as a five year grant to the International AIDS Vaccine Initiative. The initiative is a New York based non-profit making body, which wants to see three of its most promising AIDS vaccines in clinical trials by 2007. It has already enabled a joint team from Oxford and Nairobi universities to collaborate on a vaccine to produce immune responses to the A strain of HIV-1, which is the most prevalent form of the virus in Kenya. Early trials started in Oxford last year and were due to start in Nairobi last month.

The Bill and Melinda Gates Foundation, which has assets of $21bn, has been a major sponsor of vaccination programmes in developing countries. But until now the majority of Mr Gates's money has been used to distribute tried and tested vaccines. The latest donation is the largest given to AIDS research from a single philanthropist.

Mr Gates decided to support AIDS vaccine research when he discovered that efforts to develop a vaccine were waning because of lack of "market incentive." As with all his charitable donations, he researched the potential for success of various projects before committing himself to the International AIDS Vaccine Initiative. The initiative is now looking to drug companies, which have been reluctant to spend large amounts on AIDS vaccine research and development, to provide the $320m it still needs. Hank McKinnel, head of Pfizer, said, "Gates sends large amounts of money to a few organisations, but they're the very best."

Jaap Goudsmit, chairman of the initiative's scientific advisory committee, summed up the expectations of his team. "I expect we will get vaccines that do two things. They should delay disease as long as possible just like drug therapy. On top of that, they should lower disease rates. Preventing infection…will take much longer."