Breakthrough study

The US-funded study on 16,402 volunteers is a breakthrough in vaccine development for HIV/AIDS.

At a press conference in Bangkok, Thai Health Minister Witthaya Kaewparadai described the outcome of the six-year study by US and Thai researchers as a positive step forward in the search for an HIV/AIDS vaccine.

Since the disease emerged in the early 1980s, progress has been made in containing and treating the disease, but up to now there has been no sign of a vaccine or a cure.

Two-pronged approach

In the study, half of the volunteers - heterosexuals with no special risk of AIDS infection - were given a placebo. The other half were given a combination of two vaccine shots - Alvac and AidsVax - which had failed to show effectiveness when given individually.

Sanofi-Pasteur's Alvac is a disabled canary pox vaccine that smuggles HIV genes into the body and encourages the production of protective T-cells. AidsVax, currently owned by the nonprofit Global Solutions for Infectious Diseases, contains a recombinant protein aimed at stimulating a significant antibody response against the HIV protein.

Unexpected result

The study represents a revival in a campaign to find a vaccine that appeared to stall just two years ago, when use of Merck's experimental Ad5 vaccine boosted some people's chances of infection in a study.

The result of the current study was almost completely unexpected, and researchers said they couldn't figure out why the two-pronged attack of immune system vaccines was working.

But it was a triumph for the trial's supporters, who carried out the controversial study despite severe criticism.

"Myself, like others, did not think there was a very high chance that this would give any degree of efficacy," Anthony Fauci of the U.S. National Institute of Allergy and Infectious Diseases, which helped fund the study, told Reuters.

Subjects in the trial were given four doses of the Alvac vaccine and two of the AidsVax shot over six months, then monitored for three years. They were also given advice on safe sex. There were no serious side effects, the researchers said.

Not a world-wide cure

Of those who received the vaccine, 51 became infected with HIV, compared with 74 who received a placebo. Those in the study who became infected during the trial were given free access to treatment, researchers said.

Although only a small number of people were affected in the trial overall, the numbers are nonetheless statistically significant, said Adriano Boasso, an HIV vaccine expert in London.

Tests will have been done to verify that the difference is unlikely to have occurred by chance and I have no trouble believing the figures," Boasso told BBC news.

The vaccine trial doesn't indicate that a worldwide cure is around the corner. Jerome Kim, a deputy director of science at the Maryland-based Walter Reed Army Institute of Research, which sponsored the trial, stressed that the vaccine may not work in the people and places where HIV is most common - in Africa, among men who have sex with men, and among injecting drug users.

"The vaccine was tested in Thailand and it is really specific for the strains that are circulating in Thailand now," he said.

But he stressed the importance of the trial, saying that "although the results were modest … (the study) gives us hope that a globally effective HIV vaccine may be possible in the future."

Mitchell Warren, director of the New York-based AIDS Vaccine Advocacy Coalition, stressed the positive implications of the results in an interview with Bloomberg news service.

"Wow," said Warren, whose group was not involved with the study. "We are in a new place in the search for an AIDS vaccine. It's safe to say that the scientific community is caught off-guard."

The two main United Nations agencies dealing with HIV/AIDS, the World Health Organization and the UNAIDS agency, also said they were "optimistic" about the "encouraging" results.

'More work ahead'

The agencies noted that it may not be possible to get licensing permission for the drug at the moment based on the limited results, and that further studies would have to be done to determine if the vaccine has the same effect in other parts of the world.

"However, these results have instilled new hope in the HIV vaccine research field and promise that a safe and highly effective HIV vaccine may become available for populations throughout the world who are most in need of such a vaccine," they said in a statement.

"Much more work, though, has to be done by the principal investigators and a large group of international collaborators to analyze the trial data, understand the protective mechanism,

determine the duration of protection, and map next steps," the agencies said.

Also, the UN urged that once an HIV vaccine does become available, "it will need to be universally accessible by all persons at risk."

Thailand has an estimated 600,000 people who are living with HIV/AIDS. About 400,000 Thais have died of AIDS-related diseases since the virus was first detected in the country in the mid-1980s.

jen/dpa/AFP/reuters

Editor: Louisa Schaefer