US scientists reject promise of Aids vaccine

DANNY PENMAN

One of the main potential Aids vaccines will not work, according to an American research team.

Aids research groups around the world had pinned their hopes on using "attenuated", or weakened, strains of HIV as the basis of a vaccine against Aids. Live attenuated viruses are used as vaccines in diseases ranging from measles to polio and many scientists believed they offered the best chance of countering HIV.

But scientists at the Dana Farber Cancer Institute in Boston, Massachusetts, have found that an attenuated strain of SIV - a relative of HIV - which causes a type of Aids in monkeys, can still cause the disease.

Ruth Ruprecht and her team have discovered that a strain of SIV, with a disabled set of genes that are believed to be crucial to the virulence of the virus, can still cause the disease if the host is very young, or if the immune system is weakened.

Dr Ruprecht believes that a patient vaccinated against the disease, using the same approach, could develop Aids if their immune systems became compromised for even a relatively short time, for example, during a bad dose of the flu. Even the less effective immune systems found in the elderly may allow the disease to develop after a lifetime of immunity from HIV.

The findings are the latest in a long line of discoveries that have dashed the hopes of researchers trying to produce a vaccine against Aids.

The rapid mutation rate of the virus and its high level of genetic recombination - its equivalent of sex - all work against the development of a vaccine and increase the chances of the disease becoming more virulent.

The difficulties of developing a vaccine have now led many scientists to suggest that the aim in the near and medium terms should be to develop vaccines that slow the onset of the disease, rather than struggling to develop one that completely prevents it.

Dr William Paul, of the National Institutes of Allergy and Infectious Diseases in Bethesda, Maryland, said that despite the setbacks there had been "substantial progress" in understanding the disease.

For the short-term, he said: "Its time for us to realise that there are powerful ways of limiting the replication of the virus and that can fundamentally alter the course of the disease."