SCIENTISTS have warned that there are still formidable obstacles preventing them developing an Aids vaccine despite the announcement on Friday of a successful vaccine against Aids in monkeys.
One leading researcher said a human vaccine was still 'light years away' because of the exceptional difficulties posed by HIV, the human immunodeficiency virus, which is fast becoming the most studied infective agent ever.
Scientists in the United States who carried out the monkey research heralded their results as the most impressive they have yet witnessed and called for 'limited safety testing' of a similar vaccine on human volunteers. Ronald Desrosiers, head of the research team at the Harvard Medical School, Massachusetts, said the vaccine even protected monkeys that had been given enough virus to kill 1,000 animals.
'None of our vaccines using other products has come anywhere near this level of protective effect,' he said. 'This is far and away the most impressive protection effects that we've seen.'
The researchers developed the vaccine from 'live attenuated' strains of the monkey Aids virus, SIV. In effect, the vaccine is a living virus that has been genetically altered to make it less able to replicate, thereby rendering it harmless, the scientists believe.
Monkeys given the vaccine two years ago are still healthy, despite repeated injections with virulent strains of SIV. Some scientists are excited by the results because live attenuated vaccines in humans - such as those developed against polio and measles - are the best form of protection against known killers.
But Aids poses such difficulties that few scientists believe we are anywhere near to using live attenuated strains of HIV on humans. 'A live attenuated HIV vaccine is light years away,' said Peter Greenaway, head of pathology at the Government's Centre for Applied Microbiology Research at Porton Down, Wiltshire, where much of Britain's Aids vaccine research is done. 'The crux of the problem is that you just don't know the long-term side-effects of these attenuated viruses. I wouldn't volunteer for one.
Andrew McMichael, professor of immunology at the Institute of Molecular Medicine at Oxford, said that, unlike polio and measles, the Aids virus integrates itself into the genes of the patient, making a vaccine based on a live virus extremely risky because it will never be eliminated from the body. A vaccine that is safe may mutate into a virulent form.
'If you are going to give such a vaccine to children or adolescents it may cause Aids in 20 years, and how are you going to find out except by waiting 20 years and by then it's too late,' he said.
But, he added, if there was a way of ensuring that the vaccine could be made absolutely safe, 'there is a possibility of thinking the unthinkable' and using a live attenuated strain of HIV. However, like Dr Greenaway, he is pessimistic about any effective and safe vaccine against Aids being found this century.