HIV Vaccine Study Halted Due to Failure to Prevent Infection

Megan Brooks

April 26, 2013

A US government–funded phase 2b study of an experimental HIV vaccine has been shut down because the vaccine did not prevent HIV infection or reduce viral load among vaccine recipients who became infected with HIV, the National Institutes of Health (NIH) announced April 25.

The vaccine's failure came to light during a scheduled interim data review by an independent data and safety monitoring board (DSMB), the agency said.

The vaccine consists of a 2-part regimen that includes a single recombinant DNA-based vaccine, delivered in a series of 3 immunizations over the course of 8 weeks to prime the immune system, followed by a single recombinant vaccine administered at 24 weeks as a booster vaccine. The booster vaccine contains a weakened adenovirus type 5 to carry the vaccine contents and stimulate the immune system.

The National Institute of Allergy and Infectious Disease (NIAID)-funded HIV Vaccine Trials Network (HVTN) 505 Study began in June 2009, as reported by Medscape Medical News.

The study population consisted of men who have sex with men and transgender people who have sex with men. A total of 2504 participants were enrolled at 21 sites in 19 US cities.

In its April 22 interim review, the DSMB examined data on 1250 participants who received the vaccine regimen and 1244 who received a placebo vaccine. The primary analysis looked at participants who were diagnosed with HIV infection after having been in the study a minimum of 28 weeks. In this analysis, HIV infection occurred in 27 vaccine recipients and 21 placebo vaccine recipients.

Overall, from the day of enrollment through the month 24 study visit, there were 41 cases of HIV infection in experimental vaccine recipients and 30 in placebo vaccine recipients, the NIH said.

The interim analysis also found that the experimental vaccine failed to reduce viral load among those who acquired HIV infection at least 28 weeks after entering the study and who had been followed-up for at least 20 weeks after diagnosis. There were 30 participants with measurable viral load (15 vaccine recipients; 15 placebo recipients).

"Based on these findings, the DSMB recommended that no further vaccinations with the investigational vaccine regimen be administered. As the trial's sponsor, NIAID concurred with the DSMB's recommendation and has instructed all HVTN 505 study sites to immediately cease administering injections but continue follow-up with study participants to further evaluate the trial data," the NIH said.

At this point, it is not clear why there was a non–statistically significant increase in HIV acquisition among participants in the investigational vaccine group compared with those in the placebo group, and further analysis is needed to draw any firm conclusions, the NIH said. The study team will continue to follow-up all study participants for 5 years from the time of enrollment.

Study investigators at each of the 21 clinical trial sites have been notified of the decision to stop the study, and study participants are being asked to report to their specific clinic sites during the next few weeks to find out whether they received the investigational vaccine or placebo.

"NIAID and the HVTN 505 study team are working to thoroughly analyze the study data to better understand why the vaccine did not work and to guide future vaccine development efforts. Detailed scientific findings will be made publicly available as soon as possible," the NIH said.