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Researchers acknowledge potential link between vaccine and increased risk of HIV; still urge caution
Researchers acknowledge potential link between vaccine and increased risk of HIV; still urge caution
by Liz Meyer - SGN Staff Writer

In late October, Seattle Gay News reported on Merck V520-023, the experimental HIV vaccine that AIDS researchers warned may have increased South African test participants' susceptibility to contracting the disease.

On Wednesday, AIDS researchers met in Seattle for an open scientific session. There, they confirmed not only that Merck's Investigational HIV Vaccine was not effective, but also that there were more infections here in the U.S. in those volunteers who received the vaccine than in those who received the placebo.

"Study volunteers are being counseled about the possibility that those who received the vaccine may be more susceptible to developing HIV infection when exposed to HIV," said a press release from Merck, the pharmaceutical giant that developed the vaccine, and the HIV Vaccine Trials Network (HVTN), the Seattle-based organization that co-sponsored the trials. The HVTN is funded by the National Institute of Allergy and Infectious Diseases (NIAID).

The vaccine cannot cause HIV infection, and medical experts are quick to point out that a variety of factors might explain why more study participants who took the vaccine acquired the virus than did those who took a placebo. But while they urged caution in making a definitive connection between the vaccine and a higher risk of acquiring HIV, researchers made more concessions in acknowledging that potential link at the informational session.

"The current STEP results suggest that those who received the vaccine might have an increased susceptibility to acquiring HIV infection, particularly those volunteers who had higher levels of pre-existing immunity to Ad5 because of prior natural exposure to Ad5," said the press release.

The vaccine was created using a mixture of three components, each made with something similar to one of the common cold viruses, adenovirus type 5 (Ad5). The disabled cold virus, Ad5, served as a carrier for three synthetically produced HIV genes. Unlike traditional vaccines that coaxed the body to create antibodies to protect against a target virus, V520-023 was designed to coach immune system cells to attack the virus that causes AIDS.

The disparity between the vaccine group and the placebo group was more pronounced in those volunteers who had more immunity to the disabled cold virus used in the vaccine. That is, those volunteers who received the vaccine and who had very high levels of immunity to Ad5 because of earlier exposure to it were more likely to acquire HIV.

"The data from this trial are remarkably complex. We are analyzing the data to try to determine if the results are due to immune responses induced by the vaccine, differences in study populations, or some other biological phenomenon we don't yet understand, or simply due to chance," said Keith Gottesdiener, M.D., Vice President of Merck's Vaccine and Infectious Disease Clinical Research. "It will take some time before we understand why the vaccine did not work and why there was a trend toward more cases of infection in volunteers who received the vaccine."

Last week, a clinician involved with the Seattle STEP trials echoed the need to take caution in analyzing that trend.

"The idea that people who received the vaccine were at an increased risk is not a fact," said David Berger, a clinician in the Seattle STEP trials, in a telephone interview last week.

All of the 119 Seattleites who participated in the STEP trial had already received all of the injections by the time the review board had decided to halt the vaccinations, Berger said. He added that though the vaccines have been stopped, the trial has not.

Sarah Alexander, Associate Director for Communications and External Relations for the HVTN, said last month that test sites had been calling participants after the decision to halt the vaccinations was made. Test sites were calling "every single one" of the volunteers to keep them informed about the study, she said.

Now, Alexander said the HVTN and Merck face the tough choice of trying to determine when they will "unblind" participants. If researchers tell all of the volunteers now whether they received the vaccine or the placebo, the study could be compromised, said Alexander.

The Nov. 7 meeting in Seattle was to address a plan for un-blinding participants, said Alexander. However, that plan does not appear to have been formulated yet, and may come later this month.

"Whether we continue in a blinded fashion with the study or have participants be un-blinded, there are scientific advantages either way," Alexander added.

The STEP clinical trial began enrolling about 3,000 volunteers in 2004 for study sites in Australia, Brazil, Canada, the Dominican Republic, Haiti, Jamaica, Peru, Puerto Rico and the United States.

The South African trials were tested in the separate "Phambili" study administered by the HVTN and the South African AIDS Vaccine Initiative. However, both used the same Merck vaccine. The STEP clinical trial focused primarily on Gay male subjects, while the Phambili study involved more heterosexual participants.
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