HIV Vaccine Study Shows Promise

News in Context |
September 28, 2009

HIV Vaccine Study Shows Promise

  1. Frances H. Priddy, MD, MPH

A new vaccine regimen, tested among more than 16,000 young adults, was found to offer modest protection against HIV acquisition.

  1. Frances H. Priddy, MD, MPH

For the first time ever, an investigational vaccine regimen has shown some efficacy, albeit modest, in preventing HIV acquisition. The prime-boost regimen involves a combination of two previously tested vaccines — ALVAC-HIV and AIDSVAX B/E — that were designed to protect against clades B and E. ALVAC-HIV consists of three genetically engineered HIV genes (env, gag, and pro) and a live-canarypox vector, whereas AIDSVAX B/E consists of genetically engineered gp120.

The regimen was tested in a phase III trial in Thailand among more than 16,000 adults aged 18 to 30 at average risk for HIV infection. Half received two doses of ALVAC-HIV alone, followed by two doses of both ALVAC-HIV and AIDSVAX B/E, over a 6-month period; the other half received placebos. For the next 3 years, all participants underwent HIV testing and behavioral counseling every 6 months.

During follow-up, 51 of the 8197 people in the vaccine group acquired HIV infection, compared with 74 of the 8198 in the placebo group. The difference — which represents an absolute reduction of 0.3% and a relative reduction of 31% — was statistically significant. Vaccination did not appear to reduce viral load among those who became infected. The vaccine regimen was safe and well tolerated, and there was no evidence that participants increased high-risk behavior during the trial.


“It's been a long, a long time coming/But I know a change gonna come” (Sam Cooke).

Finally, after years of inching progress and bitter letdowns, AIDS researchers have shown that a vaccine can protect people, at least partially, against HIV infection. The initial reaction to this news is likely to be a collective “hallelujah!” from the rooftops of researchers, policymakers, economists, advocates, funders, patients, and the millions at risk for HIV across the globe. However, along with this success comes a host of fascinating questions and complex challenges.

How did the combination of these two vaccines work to protect against HIV? (AIDSVAX B/E was not efficacious alone in a previous phase III trial among injection-drug users in Bangkok, Thailand, and ALVAC-HIV was never even tested alone for efficacy because it did not induce sufficient immune responses in phase 2 trials.) Was one vaccine in the present trial more responsible for protection than the other? Were there other demographic, behavioral, genetic, or virologic determinants of protection? Was there an immunologic correlate of protection that could be used to fast-track development of other AIDS vaccines? Should a vaccine with modest impact be brought to market and/or used as a standard against which to compare subsequent AIDS vaccine candidates?

To address these questions, the scientific community eagerly awaits more-detailed results of the study, which will be presented in October at the AIDS Vaccine Conference in Paris. Overall, these are challenges that AIDS vaccine scientists are delighted to have to face.

Dr. Priddy is Senior Director, Medical Affairs, International AIDS Vaccine Initiative, New York.


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