The STEP Trial: Discontinuation and Unblinding
The STEP Trial: The STEP study was a phase II multinational, randomized, double-blind, placebo-controlled clinical trial which was started in 2004.
The Investigational Drug: The V520 HIV vaccine candidate is a combination of 3 components made from a weakened adenovirus type 5. The vaccine serves as a vector of 3 synthetically produced HIV genes known as gag, pol and nef. These HIV genes would supposedly induce “an HIV-specific immune response through the body’s own CD8 T-cells, which become programmed to recognize and kill HIV infected cells.”
The Sponsors: The STEP trial was sponsored by Merck, the National Institute of Allergy and Infectious Diseases (NIAID), and the HIV Vaccine Trials Network (HVTN).
The The Study Population: 3,000 HIV-negative participants from different ethnic groups. They are aged between 18 and 45 years of age and at high risk of HIV infection. The trial was conducted in the United States, Peru, Brazil, Dominican Republic, Haiti, Jamaica, Australia, and South Africa.
The Efficacy Endpoints: The primary efficacy endpoints were to evaluate the ability of the vaccine to prevent HIV infection and to reduce virus proliferation in infected individuals.
The Discontinuation: On 21 September 2007, Merck announced the discontinuation of the STEP study due to poor efficacy profile. The vaccine did not prevent infection nor reduce viral loads in the bloodstream of HIV-positive individuals.
The Unblinding: In November 2007, Merck and HVTN announced their decision to unblind the trial based on concerns that the vaccine may actually have induced susceptibility to HIV infection in study participants. Sources:
HVTN Press Release 13 Nov 2007
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