Tragic Victims War on AIDS?

Cancelled HIV vaccine might have increased risk of becoming HIV positive


New evidence suggests that Merck's experimental HIV vaccine was ineffective among some trial participants with a pre-existing immunity to a common cold virus and might have increased their susceptibility to HIV infection.

However, the researchers also said that the findings could be a statistical coincidence and that there is insufficient data to determine the full meaning of the findings.

Merck in September announced that it had ended its Phase II trial, which began in late 2004 and involved 3,000 HIV negative volunteers, after its experimental vaccine failed to prevent HIV infection in participants or prove effective in delaying the progression of the virus to AIDS. The trial was stopped by the Data and Safety Monitoring Board, an independent overseer.

Researchers late last month asked more than 3,000 people who participated in the trial to return to study sites for tests and additional follow-up regarding a possible increased risk of HIV.

Researchers in South Africa who were testing the same vaccine have told the 801 participants in the separate trial if they received the vaccine. A recommendation on whether to tell the 3,000 people enrolled in the study in the US and Latin America will be made in about 10 days.

A preliminary analysis of the trial data released in September that examined about half of the participants in the trial indicated that those receiving the vaccine were becoming HIV-positive at about the same rate as those receiving a placebo, the Times reports. There were 24 HIV infections among those vaccinated, compared with 21 among those who received a placebo. However, a new analysis of all the trial participants found that there were 49 HIV infections in the vaccinated group, compared with 33 in the placebo group.

In addition, researchers found that increased susceptibility to HIV infection among people who received the vaccine was primarily among a group of people who had a pre-existing immunity to the common cold virus adenovirus type 5.

Researchers said possible reasons for the findings included behavioural factors unrelated to the biology of the vaccine, differences in circumcision rates among the participants, variations in the strain of HIV that infected participants or that the results occurred by chance.

Source: Kaiser Network 08/Nov/07

 

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