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HIV vaccine candidate discontinued
Monitoring board said HIV vaccine V520 would not meet primary endpoints.
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A phase-2 clinical trial of investigational HIV vaccine V520 was discontinued because the vaccine was not effective.
V520 (Merck) is a mixture of three components made of a weakened version of adenovirus type 5 and three synthetically produced HIV genes.
Spokespersons for Merck and the HIV Vaccine Trials Network (HVTN), co-sponsors of the clinical trial, made the announcement Sept. 21.
“This is a huge disappointment for all of us who have been involved in the search for an HIV vaccine,” Glenda Gray, MD, principal investigator of the HVTN-sponsored trial said. “The scientific community must continue the race to find a vaccine to help secure an HIV free generation for the future.”
The trial to examine the efficacy of V520 included multiple clinical trial sites in North America, South America and Australia. Enrollment began in December 2004. The trial enrolled 3,000 HIV-negative participants between 18 and 45 years of age at high risk for acquiring HIV. Half of study participants received three doses of vaccine over three months while the other half received placebo.
Two primary endpoints were whether the vaccine prevented infection and whether the vaccine reduced the amount of virus in those who acquired HIV.
Lack of prevention
The vaccine did not prevent infection. Among participants who received at least one dose of the three-dose vaccine series (n=741), 24 people acquired HIV. In the placebo group (n=762), 21 people acquired HIV. In a subgroup of participants who received at least two vaccinations and were HIV negative for the first 12 trial weeks (n=672), 19 people acquired HIV. Eleven people acquired HIV in the placebo group (n=-691).
The vaccine also did not reduce the amount of HIV virus in the blood of participants who acquired HIV. HIV RNA levels at eight weeks to 12 weeks after infection diagnoses were similar in both the vaccine cohort (mean HIV RNA 40,000 copies/mL) and the placebo cohort (mean HIV RNA 37,000 copies/mL).
The Independent Data Safety Monitoring Board recommended the discontinuation of the trial after a review of safety data and interim efficacy analysis. The interim analysis was conducted on about 1,500 participants expected to have the best responses to the vaccine because of their low levels of pre-existing immunity to adenovirus 5. The trial would not meet its primary endpoints, according to board findings.
Investigators were instructed to stop vaccinating study participants and to continue monitoring the cohort per protocol. Additional analysis and monitoring is ongoing.
A second phase-2 trial of V520 in South Africa and two additional phase-1 trials have also been discontinued.
“While we are very disappointed that this vaccine candidate did not demonstrate protection, data from the trial will provide critical insights into the disease and future vaccine development,” said Larry Corey, MD, principal investigator for HVTN.