HIV Vaccine :: Merck’s investigational HIV vaccine not Effective

Vaccination in a phase II clinical trial of Merck & Co., Inc.’s investigational HIV vaccine (V520) is being discontinued because the vaccine was not effective.

The announcement was made by the co-sponsors of this clinical trial, Merck & Co., Inc., and the HIV Vaccine Trials Network (HVTN), which is funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the U.S. National Institutes of Health.

The trial, called STEP, was an international phase II “test of concept” trial in uninfected volunteers at high risk for acquiring HIV infection. The independent Data Safety Monitoring Board (DSMB) for STEP reviewed safety data and results of an interim efficacy analysis of the study, and recommended that vaccination be discontinued because the STEP trial will not meet its efficacy endpoints.

Study investigators have been instructed to discontinue vaccinating volunteers in this study and to monitor them in accordance with the study protocol. Enrollment and vaccination in a second Phase II trial of this vaccine being conducted by the HVTN in South Africa called Phambili, and two additional Phase I trials, have been discontinued. The DSMB for the Phambili trial will evaluate the available data.

The Merck vaccine candidate is a mixture of three components, each made with a weakened version of a common virus (adenovirus type 5), that serves as a carrier, or delivery vector, along with three synthetically produced HIV genes known as gag, pol and nef.

The STEP study (HVTN 502, Merck V520 Protocol 023) was a multicenter, randomized, double-blind, placebo-controlled phase II test-of-concept clinical trial. The trial enrolled 3,000 HIV-negative volunteers from diverse backgrounds between 18 and 45 years of age at high risk of HIV infection.

The study evaluated two primary efficacy endpoints: whether the vaccine prevented HIV infection and whether the vaccine reduced the amount of virus in those who developed infection. As planned, an interim efficacy analysis was conducted in the approximately 1,500 volunteers expected to have the best response to the vaccine because they had low levels of pre-existing immunity to adenovirus 5.

The vaccine did not prevent infection: in volunteers who received at least one dose of the three-dose vaccine series, 24 cases of HIV infection were observed in the 741 volunteers who received vaccine and 21 cases of HIV infection were observed in the 762 participants in the placebo group. In the subgroup who had received at least two vaccinations and who were HIV negative for at least the first 12 weeks of the trial, 19 cases of HIV infection were observed in the 672 volunteers who received vaccine and 11 cases were observed in the 691 volunteers who received placebo. In addition, the vaccine did not reduce the amount of virus in the bloodstream of those who became infected; HIV RNA levels approximately 8 to 12 weeks after diagnosis of infection were similar in the vaccine and the placebo arms. The geometric means of the HIV RNA levels in the blood of infected individuals, the standard measure of ongoing HIV replication, were approximately 40,000 copies/mL in the vaccine group and approximately 37,000 copies/mL in the placebo group. Additional analyses will be conducted on the entire study population and will be shared with the scientific community.

Study volunteers were followed for approximately 13 months. Overall adverse event rates were generally similar among the two groups, except for a higher rate of local injection-site related reactions in the vaccine group.

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