Fauci also disagreed that all current field trials of HIV vaccines were futile. He declined to comment on whether the latest developments would put off or even cancel the launch of a major federally funded clinical trial, called PAVE 100, of another HIV vaccine that hasdsome similarities with the failed Merck candidate.

Desrosiers' speech added to the train of bleak news at this year's conference, where on Monday researchers revealed that a study testing treatment of herpes infection with common pills found the intervention failed to reduce risk of HIV infection.

He said the research community must come to grips with the unpleasant fact that HIV is the 'undisputed champion' among viruses in its ability to mutate resistant strains. Gene fingerprint tests show, for example, that a single infected individual carries more genetic variants of HIV than the flu virus - a notoriously changeable bug - will evolve worldwide each year. 'It has the uncanny ability to replicate continuously, no matter what we throw at it,' he said. 'And we don't even know what constitutes an effective immune response.'

Dr. Susan Buchbinder, chief of HIV research for the San Francisco Department of Public Health and a lead investigator in the Merck drug trial, said she still believes it was not a mistake to have launched that trial, or to consider carrying out others. 'We have a huge epidemic on our hands,' she said.

She reported at the conference Tuesday that further analysis of the Merck study results found that uncircumcised volunteers who received the vaccine ran nearly four times the risk of infection than those who were given a placebo.

Buchbinder said one possible explanation was that the vaccine somehow activated white blood cells near the surface of the foreskin - known HIV targets - making them more vulnerable to infection. She told reporters that she would not recommend at this time that study participants who were uncircumcised and received the vaccine, rather than a placebo, be circumcised as a precaution.

Follow-up research has also shown that the slight trend toward higher infection rates among all those who took the vaccine has not yet abated. But the number of infections involved is so low that there remains a possibility that the higher infection rate among uncircumcised men was purely the result of chance.

About 133 men in San Francisco volunteered for the international study, which enrolled 3,000 men and women worldwide. Buchbinder said the researchers keep in touch with the volunteers, who have been understanding about the results. 'They are heroes,' she said.

Mitchell Warren, executive director of the AIDS Vaccine Advocacy Coalition in New York, said research in the field has come to a critical junction. 'I don't think we can abandon clinical trials,' he said. 'I don't think we have that luxury.'

Source-Medindia
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