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. This vector was based on an adenovirus called adenovirus serotype 5 or Ad5. Adenoviruses are cold-causing viruses. Ad5 was disabled for use as a vector so that it was safe and did not cause any illness 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 reduce viral load in HIV-negative 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 that showed that the candidate is safe for use in humans.
Participants: 3,000 HIV-negative men who have sex with men and high-risk heterosexual men and women
Countries: Australia, Brazil, Canada, Dominican Republic, Haiti, Jamaica, Peru, Puerto Rico, US
Trial sponsors and collaborators: HIV Vaccine Trials Network (HVTN), Merck, US National Institutes of Health (NIH)
When were results released? Immunizations in the trial were stopped early (September 2007). The data analysis found no evidence of benefit, and potential for increased risk of HIV infection among Ad5-seropositive, uncircumcised men. Follow-up continues.
To learn more visit:
http://www.avac.org/vax_update.htm