The HIV Vaccine Trials Network (HVTN), part of the National Institutes of Health (NIH), has decided to proceed with a phase IIa safety study of an HIV vaccine produced by the company GeoVax.

The GeoVax vaccine differs somewhat from the Merck vaccine that recently proved to be ineffective in the STEP trial. The Merck vaccine used a modified cold virus to deliver pieces of HIV’s genetic material to the immune system. The GeoVax first primes the immune system by directly delivering pieces of HIV DNA, followed by a booster shot of a disabled form of the smallpox virus, called modified vaccinia ankara (MVA). The MVA boost is designed to amplify the immune system’s initial response to the HIV DNA prime.