Rationale: MRK-Ad5 was a vaccine candidate that combined synthetic fragments of HIV with a vector, or delivery system, designed to induce strong immune responses. The vector that was used was based on an adenovirus called adenovirus serotype 5 or Ad5. Adenoviruses are cold-causing viruses. The Ad5 vector was adapted so that it could not cause disease in humans. The fragments of HIV contained were selected because of evidence suggesting that immune responses against these parts of HIV can help control or prevent HIV infection. Phase I and II studies of the candidate, which were conducted prior to the launch of Step/HVTN 502, showed high rates of immune responses (as evaluated by common tests or assays) and the candidate appeared to be safe. The study was designed to give a preliminary indication of whether this vaccine strategy can reduce the risk of HIV infection and/or blunt the severity of HIV disease in people who are vaccinated and go on to acquire HIV.
Study Question(s): This study was designed to see whether immunization with MRK-Ad5 reduced the risk of HIV infection via sexual transmission, and whether those who were immunized with MRK-Ad5 and went on to become infected with HIV had a lower viral set point than people who received the placebo and later became infected. The trial was also designed to gather information on safety to confirm and expand on earlier findings, which showed that the candidate is safe for use in humans.
Participants: The trial planned to enroll 3,000 HIV-negative men and women, but the trial was stopped early before enrollment could be completed.
Country: South Africa
Trial sponsors and collaborators: HIV Vaccine Trials Network (HVTN), Merck, South African AIDS Vaccine Initiative (SAAVI), US National Institutes of Health (NIH)
When were results released? Immunizations and enrollment in the trial were stopped early (September 2007) following the Step trial announcement. Follow-up continues.
To learn more visit:
http://www.saavi.org.za/1press2007.htm
http://www.clinicaltrials.gov/ct/show/NCT00413725?order=8
http://www.hvtn.org/faq/503/HVTN503FAQ_eng.pdf