Background:  Currently, 3 efficacy trials of HIV vaccine candidates are underway and a fourth efficacy trial is planned for initiation later this year. These trials will include more than 30,000 volunteers from 16 countries in North and South America, the Caribbean, Asia, southern Africa and East Africa. Results from the efficacy trial in Thailand of the combined canary pox and protein subunit vaccine and VTN 502 evaluating the Merck Adenovirus type 5 vaccine are expected in late 2009. All 4 efficacy designs include evaluation of both acquisition of HIV as a primary endpoint, as well as reduction of viral burden in HIV infected vaccine study volunteers. The individual designs offer distinct features in respect to volunteer risk, HIV genetic components, and subtype breadth and endpoint definition. Follow-up of HIV-infected volunteers is incorporated, to some extent, in some trials, or referred to a sister study in others.

Conclusions:  However, the clinical import of alterations in viral burden among infected volunteers who have received vaccine is not known. Should vaccination produce a favorable reduction in viral burden in any of these studies, additional research will be required to define the associated clinical benefit.