The quest for an AIDS vaccine has suffered another setback. The National Institutes of Health announced April 25 that it had stopped immunizing volunteers with the experimental vaccine known as HVTN 505 because it had become clear that the vaccine doesn’t prevent HIV infection.
Since the trial began in 2009, 1,250 volunteers had received the vaccine and 1,244 others had gotten a placebo — both as a series of shots over 24 weeks. Most participants were men who have sex with men. Among volunteers who had been in the study for at least 28 weeks, 27 infections occurred in those getting the vaccine and 21 in placebo recipients. Of all study participants, regardless of how long they were in the study, 41 HIV infections showed up in vaccinated volunteers and 30 in those who got the placebo.
The vaccine used a double-hit strategy designed to rev up immune protection. Three early shots were intended to prime the immune system. Then, 16 weeks later, participants received a booster shot that delivered genetic material that made molecules produced by HIV, with the goal of eliciting an immune response against the virus. The vaccine could not itself cause HIV infection.
An independent data and safety monitoring board assessed the results collected as of April 22 and recommended stopping the trial. The National Institute of Allergy and Infectious Diseases, which sponsored the trial, agreed. NIAID and the study investigators will continue to monitor volunteers for five years and analyze the data.