The trial will involve up to 3,000 participants at five sites throughout South Africa and is expected to continue for four years.
“This trial will answer several major scientific issues that face all of us in the field of HIV-vaccine development,” said Lawrence Corey, principal investigator of the HIV Vaccine Trials Network.
“It will determine the usefulness of vaccines that induce high immune response to the parts of the virus that are similar between different strains of HIV-1.”
Merck’s test vaccine, known as the MRKAd5 HIV-1 trivalent vaccine, has already been studied in phase I and II trials. In those previous trials this vaccine was found to be safe and to stimulate cellular immune responses against HIV in more than half of volunteers.
The phase IIb study will attempt to determine whether the test vaccine prevents HIV infection, results in lower HIV levels in those who become infected after vaccination or both. In addition, investigators will determine if this vaccine, which is based on clade B HIV, has the potential to protect against the clade C virus, the subtype prevalent in South Africa.
Additionally, the South African study is likely to provide important new data on how the test vaccine might work in a predominantly heterosexual HIV epidemic, how well the vaccine works in women, and whether the vaccine works in populations with pre-existing immunity to the viral vector used in the vaccine.
“South Africa is an excellent location for this trial due to the high levels of infection coupled with the good clinical infrastructure, including internationally recognized immunology laboratories, a well-established national vaccine initiative and experience in running clinical trials,” said James Kublin, one of study’s lead investigators.