Top 10 for '09: No. 4

No. 4: Medical Science Crawls Toward an HIV Vaccine

In October, peer-reviewed results of a mammoth Thai trial (>16,000) showed modest (and possibly statistically significant) protection against HIV infection after a series of shots in moderate-risk adults. The trial results, although only marginally positive, are generating optimism after 2 decades of failure and, specifically, 3 negative trials (published in 2005, 2006, and 2008) of assorted vaccine regimens in high-risk adults.

In the latest placebo-controlled Thai study, vaccine efficacy—defined as the percentage reduction of HIV infection—climbed to a significant 31.2% in the modified intent-to-treat analysis.* Compare this value with the highest estimated vaccine efficacy in the previous large-scale studies, only 6%, and you get an idea of why some investigators believe that we're actually getting somewhere.

The trial's vaccine regimen consisted of 4 "priming" injections of a recombinant canarypox-vector vaccine (Alvac-HIV; sanofi-pasteur) and 2 booster shots of a recombinant glycoprotein-120 subunit vaccine (AIDSVAX B/E; VaxGen). The prime-boost vaccination series was chosen on the basis of previous trials (Belshe et al, 1994; Russell et al, 2007; and AIDS Vaccine Evaluation Group 022 Protocol Team, 2001), wrote the study investigators. Previously unsuccessful vaccine regimens in high-risk adults consisted of 7 injections of VaxGen's AIDSVAX B/B vaccine; 7 injections of VaxGen's AIDSVAX B/E vaccine; and 3 injections of Merck's trivalent adenovirus-vector vaccine.

The next steps are to determine the immune mechanisms that conferred protection in the Thai trial and to create a vaccine that will maximize those responses.

HIV = human immunodeficiency virus.

* Which excluded 7 individuals who were discovered to have HIV infection at baseline.