South Africa Aids-Vaccine Trial Volunteers Warned of HIV-Infection Risk

Tamar Kahn
Business Day
Oct. 29, 2007

Researchers are recalling people who took part in the aborted Phambili AIDS-vaccine trial to tell them the product could have increased their susceptibility to HIV infection, should they be exposed to the virus by unprotected sex or dirty needles.

Phambili was the local arm of an international phase IIb study to test Merck's MRKAd5 candidate AIDS vaccine. The trial was stopped last month after an independent data and safety monitoring board analysed the international arm of the study, called Step, and found the vaccine did not prevent HIV infection, or reduce the amount of virus in those who got infected.

The Step arm of the study enrolled 3000 participants in Latin America, the Caribbean and the US, starting in 2004. Unlike the South African arm, where most volunteers were heterosexual women, most of the Step volunteers were men who had sex with men. The interim analysis of people who got at least two of the three planned immunisations in the Step arm found 19 cases of HIV infection among the 672 volunteers who received the test vaccine, and 11 infections among the 691 who got a dummy version.

Scientists are confident the vaccine itself could not cause infection, but are still analysing the data from the Step trial to try to understand why there were more infections in the group of volunteers who got the candidate vaccine, said the Phambili study's principal investigator Dr Glenda Gray.

It appeared the vaccine might have made people more vulnerable to infection if they were exposed to HIV, but scientists could not be certain as analysis of the data collected was continuing, she said.

Scientists were continuing to investigate whether factors such as high-risk sex, genital ulcers and injecting drugs could have also played a role, she said.

"The bottom line is we don't yet know what the data means. It's very hard to translate what is happening in the US to SA," said Gray. "We decided it would be prudent to advise people in our trial that in the US, among men who had sex with men, there seems to be an increased risk of susceptibility (of HIV infection) among people who got the vaccine," she said. Phambili started later than Step and had enrolled only 801 of the 3000 people it was planning to when the trial was stopped, she said.

Only 55 of the participants received the full course of three shots -- 27 got the vaccine and the rest a dummy version. About 200 people got only one shot, half of whom got the test vaccine.

Phambili volunteers will be told whether they got the test vaccine or the dummy version, and will get counseling and three monthly HIV tests, Gray said, adding that the vaccine itself cannot cause HIV. If the participants abstained from sex, did not have sex with infected partners, or use condoms, they could not get infected," she said.

Prof Anthony MBewu, president of the Medical Research Council, said: "It took almost 50 years to find a polio vaccine and HIV is proving to be a tricky adversary. However, every trial gives us additional and valuable information about how to fight this virus," said MBewu.