Scientists at the 8th International Conference on Aids, in Amsterdam, said that trials would be conducted in Europe, the US and developing countries.
Dr Daniel Hoth, director of the Aids' division at the National Institute of Allergy and Infectious Diseases, in Maryland, said that more than 12 different preventive vaccines have now been tested in small trials of 20 people or less. Some were promising and side-effects were minor and shortlived. All of the vaccines stimulated the production of antibodies, proteins produced by the immune system in response to infection. Several questions remained unanswered, but it was important that preparation for the trials - recruitment, selection of sites and training - should begin now.
'The encouraging news is that the most recent trials have shown a higher frequency of neutralising antibodies which kill HIV directly,' he said.
But he warned people not to expect a vaccine soon. 'If we do not work vigorously now to set realistic expectations we will create undue disappointment and negative public reactions and the possible slowing down of efforts to find a useful vaccine.'
He said that the most compelling reason for accelerating vaccines into large trials was the hypothetical model for testing developed by the National Institute. It showed that a vaccine which is 60 per cent effective if introduced early into a high-risk population would save more lives than waiting five years for a more effective vaccine.
Dr Samuel Katz, from Duke University Medical Center, said a partially effective vaccine was not unusual. The influenza vaccine is about 80 per cent effective.
Stephen Lwanga, from the Uganda Aids Commission, said his country was willing to collaborate with developing countries in vaccine trials. But Africa should not be 'used' by the West, he said. If a vaccine became available as a result of such trials, it must be made affordable to them. 'So many drugs have been tried in African countries and yet when they are eventually found to be useful we were left out in the cold.'
Carel Ijsselmuiden, of the Medical University of South Africa, warned that a vaccine may be the 'magic bullet' but it would deny the problems which have led to the spread of HIV, such as poverty and discrimination.
Dr June Osborn, of the American National Commission on Aids, said a vaccine would not provide the answer to HIV. 'A vaccine would supplement but it cannot replace what we need to do through education.'
Dr Jonas Salk, who developed the polio vaccine, described a radical new approach to a vaccine for HIV infection. Raising antibodies against the virus was not helpful to a patient, he said. Tiny doses of vaccine which would elicit a small response from the immune system and which did not produce antibodies is more effective. Four studies support Dr Salk's theory, but further work is needed.