The US government is poised to start a new AIDS vaccine trial, prompting some to caution that it is too soon to initiate such studies after a Merck vaccine not only failed to show effectiveness but also may have increased participants' HIV infection rate.

Late last week, the NIH's AIDS Vaccine Research Subcommittee voted 23-3 in favor of beginning the PAVE 100 HIV vaccine trial. The study would be conducted by the Partnership for AIDS Vaccine Evaluation (PAVE), which is a consortium of government agencies and government-funded organizations involved in HIV vaccine research, and is sponsored by NIAID.

Dennis Burton, a Scripps Research Institute immunologist and member of the advisory panel, urged caution. "We're redesigning the aims of human HIV vaccine research without redesigning the vaccine," Burton, referring to a refocusing of AIDS vaccine research decided upon at an NIH meeting in March, told Bloomberg News. "Let's not go into a human experiment without a clear idea of what we're going to learn."

Yesterday (Jun 2), Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID) director told Bloomberg News that he would review the panel's comments and decide "reasonably soon" whether to proceed with the study. The panel's advice is not the only source from which Fauci will draw in making his decision. Fauci will also consider "the thoughts/recommendations of the various PAVE partners, HIV community groups, other NIAID scientific advisory bodies, such as the Clinical Trials Strategic Working Group," according to an Email sent to The Scientist by an NIAID spokesperson.

The new vaccine - like the failed Merck vaccine - uses a recombinant vaccine based on adenovirus type 5 (Ad5), but administers a single injection after a "prime-boost" of three DNA-based immunizations designed to stimulate the immune system. The failed Merck Ad5 vaccine was administered in three sequential injections, with no prior DNA-based priming. "The [vaccine] regimen is sufficiently different from the Merck product to warrant further testing," Eric Hunter, Emory University vaccinologist and subcommittee chair, said at the panel's meeting.

According to the NIAID, the vaccine will be tested in the US on 2,400 men who have sex with other men, but trial participants must not have detectable Ad5 antibodies and must be circumcised - the two main differences in enrollment criteria from the failed Merck trial.