2011年7月22日 | EN
Excitement about new drug treatment for HIV prevention does not mean we should lose sight of other methods, cautions Priya Shetty.
Scientists trying to prevent people from becoming infected with HIV are on a roll. After a huge leap forward last year in AIDS vaccine research, when powerful sequencing uncovered potent anti-HIV antibodies, new research shows convincingly that treatment with antiretroviral drugs can also be used to prevent infection.
The latest results on the effectiveness of drugs for pre-exposure prophylaxis (PrEP), presented at the International AIDS Society conference (IAS 2011) in Rome this week, were released just a couple of weeks before. The finding that PrEP could reduce new HIV infections by up to 73 per cent was so compelling that the trial was halted early.
With such excitement over a preventive approach that we have available right here, right now, suddenly a vaccine might not seem like the holy grail of HIV prevention after all.
But the early days of HIV vaccine research are a cautionary tale. The assumption that a vaccine was just around the corner seemed to lead, initially, to complacency that might explain why it is only relatively recently that other approaches to prevention have been high on the agenda.
And at IAS 2011, there was a broad consensus that pursuing one approach does not render the others redundant — and indeed that it would be impossible to tackle a disease such as HIV/AIDS without several approaches.
Vaccine research gets a boost…
For years, HIV prevention has relied on non-biomedical, behavioural interventions such as condom use and safe-sex counselling. Since behaviour is difficult to change, such tactics are notoriously difficult to implement. Yet, for several years, they were the only weapons in the fight to prevent the spread of HIV.
Once scientists knew that HIV was the cause of AIDS, they were confident that a vaccine would soon be developed for the virus. But they had not bargained for its complexity — and AIDS vaccine research has been problematic from the beginning.
Most disease-causing viruses come in a few different strains; HIV has hundreds of them. Not only that, the virus is capable of changing its surface proteins to evade antibodies. Devising a vaccine against HIV is a huge challenge.
Speaking at IAS 2011, Gary Nabel, head of the US National Institutes of Health's Vaccine Research Center, which was set up in 1999 to find an HIV vaccine, described most of the time spent hunting for it as "the dark ages".
But last year, everything changed, said Nabel. The discovery of antibodies that worked against 90 per cent of HIV strains (compared with 40 per cent for previously found antibodies) has made the prospect of an HIV vaccine real again.
…but existing tools show promise
Even before the resurgence in vaccine research, male circumcision and microbiocide (disinfecting) gels had shown great promise in preventing infection. The WHO now says "there is compelling evidence that male circumcision reduces the risk of heterosexually acquired HIV infection in men by approximately 60 per cent".
Early clinical trials had hinted at the promise of treatment for prevention. And in the past few months, studies have shown that combination antiretroviral treatment (tenofovir/emtricitabine) reduced the risk of HIV-negative people becoming infected by 44 per cent in men who have sex with men, and by up to 73 per cent in heterosexual couples.
A key randomised clinical trial that was also presented at IAS 2011, called HPTN 052, showed conclusively for the first time that putting infected people on antiretroviral therapy early can reduce their chance of passing on the infection by 96 per cent.
Many paths to prevention
As thrilled as HIV researchers have been with the results of preventive drug trials, the implementation of treatment programmes will be far from simple. Developing countries have too few healthcare workers, and rolling out antiretroviral treatment can be logistically difficult — so adding treatment for prevention will add to already heavy burdens.
Deciding which groups are eligible for drug treatment, which means putting otherwise healthy people on powerful drugs, also raises ethical questions that are not easily solved.
Given these complexities, it would be short sighted not to pursue aggressively a vaccine that would confer lifetime immunity in one shot. Nor should the public health community abandon non-biomedical strategies such as condom use and reducing risky behaviour.
Safe sex is not just about HIV, after all — prevalence rates of other sexually transmitted diseases are on the rise in many developing countries, and rates of unwanted pregnancy remain high.
The take-home message from IAS 2011 is crystal clear. After years of struggle, we can now contemplate moving towards ending the epidemic. But we should not threaten the chances of success by playing off one approach against another.
Journalist Priya Shetty specialises in developing world issues including health, climate change and human rights. She writes a blog, Science Safari, on these issues. She has worked as an editor at New Scientist, The Lancet and SciDev.Net.