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South Africa Aids-Vaccine
Trial Volunteers Warned of HIV-Infection Risk
Tamar Kahn
Business
Day
Saturday October 27, 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.
(Article continues below)
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.
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