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NIH Stops HIV Vaccine Immunizations in Clinical Trial

Syringe (ZaldyImg/Flickr)National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, will stop testing an HIV vaccine candidate, after interim results showed the vaccine stopped neither HIV infections nor the amount of HIV in the blood. The HVTN 505 study, a phase 2 clinical trial of safety and efficacy begun in 2009, enrolled 2,504 volunteers at 21 sites in 19 U.S. cities.

The trial tested a regimen, beginning with a first injection designed to prime the immune system containing genetic material expressing antigens with proteins from both the surface and internal structures of HIV. After 24 weeks, test subjects received a booster vaccine with an engineered and weakened adenovirus type 5 that acted as a carrier of genetic material expressing a matching set of HIV antigens.

Adenoviruses are a common cold virus, but the virus in this vaccine regimen was disabled to prevent causing a cold or other respiratory illness. In addition, the two vaccines contained neither live nor weakened HIV viruses, thus could not cuase HIV infections.

Participants in the trial, administered under the HIV Vaccine Trials Network, were men or male-to-female transgender individuals age 18 to 50 who have sex with men. Control subjects received placebo versions of both the priming and booster vaccines.

An independent monitoring committee reviewed results of 1,250 test volunteers who received the vaccine and nearly as many (1,244) placebo group participants, after at least 28 weeks, a period considered sufficient for the vaccine regimen to be given and stimulate an immune response. The review indicated 27 HIV infections occurred among the vaccine recipients, and 21 HIV infections occurred among participants receiving the placebo.

Among the volunteers who became infected with HIV after 28 weeks, 14 infections occurred among those who received the vaccine and 9 infections occurred among those receiving the placebo. Over the full 24-month timetable of the study, 41 cases of HIV infection occurred among participants receiving the vaccine, while 30 cases of HIV infection occurred among the placebo recipients.

The monitoring committee likewise measured viral load — the amount of HIV in the blood — after at least 28 weeks, and among those followed for at least 20 weeks after diagnosis. The committee found 30 participants with measurable viral load, divided evenly between 15 vaccine recipients and 15 placebo recipients.

Based on these interim results the monitoring committee recommended and NIAID concurred that the trial sites immediately cease administering injections. However follow-ups and counseling will be continued for five years from the time of enrollment. Participants in this and other NIAID-sponsored trials receive counseling on reducing the risk of becoming HIV-infected and are provided free condoms.

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Hat tip: FirstWord Pharma

Photo: ZaldyImg/Flickr

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