RxTrials Institute Drug Pipeline Alert

Merck and the HIV Vaccine Trials Network (HVTN), an international collaboration of scientists and institutions, have discontinued the STEP Phase II clinical trial evaluating Merck’s investigational HIV vaccine V520 due to lack of efficacy.

According to Merck and HVTN, the Phambili Phase II trial being conducted by the HVTN in South Africa and two additional Phase I trials of the vaccine also have been discontinued. 

The STEP study was a multicenter, randomized, double-blind, placebo-controlled Phase II test-of-concept clinical trial.  The trial enrolled 3,000 HIV-negative volunteers between the ages of 18 and 45 at high risk of HIV infection.

An interim analysis of the approximate 1,500 volunteers expected to have the best response to V520 revealed the vaccine did not prevent infection, according to the trial’s sponsors.

Of the 741 volunteers who received at least one dose of the three-dose vaccine, 24 contracted HIV. Twenty-one cases of HIV were observed in the 762-patient placebo group. In the subgroup receiving at least two vaccinations, 19 of the 672 patients in the vaccine group and 11 of the 691 patients in the placebo group contracted HIV, the cosponsors said.