For the first time in nearly three decades of research, HIV/AIDS scientists are reporting positive results from a vaccine trial. The study tested two vaccine candidates that proved ineffective when examined separately in earlier studies; in the new trial, involving more than 16,000 volunteers in Thailand, the two vaccines were combined in a “prime-boost” approach. Researchers said the two-dose vaccine cut the risk of becoming infected with HIV by more than 31 percent-a significant, if limited, result.. Dr. Mayer is also co-chair of the Center for Global Health Policy’s Scientific Advisory Committee.
Some are calling this a “milestone,” others say not so fast. We spoke with Dr. Kenneth Mayer, a professor of medicine and community health at Brown University and director of Brown’s AIDS Program, to get a better sense of what today’s news means
Q: After decades of disappointing efforts to develop an AIDS vaccine, how significant is this development?
A: It’s definitely a move in the right direction, even if it is not a home run. There are several reasons to be cautious. The first is that unless a study shows a definitive result, we would not want to make broad conclusions from a single clinical trial.
Another reason to be guarded is that the protective effect for this vaccine combination was 31.2 percent. That’s at the borderline of the threshold that epidemic modelers would consider as being able to slow the HIV epidemic, so the broader public health significance of these findings remains unclear.
The reason this is exciting nonetheless is that, if additional studies corroborate the idea of using two vaccines to provide the necessary host defenses against HIV, then this study provides a building block for the development of more effective combination vaccines. There are new and promising vaccine candidates in the pipeline that may be more immogenic than the two vaccines used in the Thailand study.
Q: So what’s the next step for this particular vaccine candidate, or the broader search an AIDS vaccine?
A: It’s not clear yet. These data were presented in advance of a major AIDS vaccine meeting in Paris, which will happen in mid-October. More details will be released and analyzed at that meeting, and that information will guide the next steps.
One line of questioning that needs to be teased out, for example, is whether the study participants who got the vaccine but who still got infected did not mount a strong immune response, but the people who were protected did mount a strong immune response. That would be very crucial information to shape the next research steps by identifying correlates of immune protection. Vaccine development, like much of science, is an iterative process, so learning as much as we can from this study will be crucial.
Q: In recent years, as scientists have become disillusioned about the prospect for discovering an effective vaccine, the focus has shifted, with some success, to other prevention efforts, such as microbicides and PrEP. Do you worry that scientific attention and/or funding could now shift back towards the search for a vaccine in light of today’s news, and if so, what are the possible ramifications of losing focus on microbicides and PrEP?
A: I would hope the promise of this new research does not divert resources from one area to another. We need all of the above. Remember, oral chemoprophylaxis, known as PrEP, and topical microbicides have to be taken regularly right now and so they could be much more expensive and rely more on people’s adherence than a vaccine, which ideally could confer a high level of protection with a few shots. The drugs are available now for PrEP, so if we can show benefit in the short run, we need to move forward with that. Microbicides also hold great promise. But ultimately to stop the epidemic in its tracks, we need a vaccine. All of this research needs to go forward, since none of us is smart enough to know what it will take to protect future generations from HIV.