AIDS vaccine may have worsened risk of HIV infection

Hundreds of South Africans who received an experimental AIDS vaccine have been warned that it may have increased their risk of HIV infection.

The study, which began in January, was meant to establish whether a product made by the pharmaceutical company Merck could protect people from HIV. It was stopped last month after researchers found no evidence of effectiveness.

Now it has been revealed that the infection rate was higher among people who received the vaccine than among those given a placebo. Nineteen vaccinated volunteers acquired HIV, compared to eleven in the placebo half of the study.

Every trial participant is now being told whether they received the vaccine or the placebo, and is being warned of the possible consequences.

Merck's vaccine candidate was separately trialled in 3,000 volunteers from the USA, Canada, Australia, Peru and the Caribbean. That study, which began in 2004, was halted at the same time as the South African trial. The ethics board has yet to decide whether to inform the participants - mostly gay men - if they received the vaccine or the placebo.

Experts say the vaccine itself could not have caused HIV infection, but it may have increased the risk of transmission by affecting immune responses.

"Given the complexity of the issue, we feel the best conclusions will be reached when all the data are analyzed in their entirety," said Mark Feinberg, vice president for medical affairs and policy for Merck.

More details are likely to emerge when vaccine researchers meet in Seattle early next month.

Not only is this outcome a major disappointment for researchers, but it may also affect people's willingness to take part in similar trials in the future. A trial of an HIV microbicide was stopped in January after it too found more infections in the treated group compared to those who received a placebo.

AVERT.org has more about AIDS vaccines and microbicides.