Despite large-scale HIV prevention initiatives around the world, including educational outreach and condom distributions, seven thousand people are still newly infected with the virus every day. Especially considering some of the hardest-hit areas and populations—for example, 25% of people in Botswana age 15-49 are infected—it's clear that we need more strategies than condoms and education alone.
So what if there were a daily pill to prevent new HIV infection? Millions of people already take pills every day to prevent pregnancy, or to fend off heart disease. With this idea in mind, new clinical trials are using antiretroviral drugs, which are already used to treat HIV, to prevent new infections. This strategy, known as pre-exposure prophylaxis (PrEP), showed positive results in two major trials just before last month’s International AIDS Society (IAS) conference in Rome, pushing PrEP into the limelight.
Both studies looked at serodiscordant heterosexual couples – that is, only one partner was infected with HIV – and found that giving the uninfected partner a daily antiretroviral pill reduced their chances of contracting HIV. The Partners PrEP trial (University of Washington) gave a daily pill to the uninfected partner in 4,758 couples in Kenya and Uganda, and found that those who received either tenofovir (TDF, also known as Viread) or a combination of tenofovir and emtricitabine (TDF/FTC, also known as Truvada) had 62% or 73% fewer infections, respectively, than those who received a placebo pill. Excitingly, the antiretroviral pills were so effective that the people assigned to the placebo were switched over to one of the drugs for the remainder of this ongoing study.
Similarly, the TDF2 trial (Centers for Disease Control and Prevention) found that a daily TDF/FTC (Truvada) pill was 63% effective at preventing HIV infection compared to a placebo pill in 1,219 serodiscordant couples in Botswana. Last year’s Pre-Exposure Prophylaxis Initiative (iPrEx) study of 2,499 men who have sex with men found a similar 44% reduction in HIV acquisition with a daily TDF/FTC pill. (Here is some more information about PrEP).
Based on these results, it’s clear that PrEP works, and judging from the interest these results generated at the IAS meeting in Rome, it’s clear that this is an exciting idea. Now we need to figure out the best way to use it. One obvious issue with scaling up the use of PrEP is money, and with resources scarce even for treating those who are already infected, it will be critical to figure out who will benefit most and how to make it available to these people.
One theme emerging from recent HIV prevention research is that we don’t have a magic bullet, but we do have a lot of tools to work with. Instead of simply looking for one perfect prevention strategy, we need to focus on understanding the best ways to use these tools together. For example, an effective vaccine would certainly be a better prevention strategy than a daily pill, but until one is developed, combining a partially effective vaccine with daily PrEP could be more effective than either method alone.
But even with the best biomedical prevention methods, there will always be a behavioral component that must be addressed. As one speaker at the IAS conference reminded us, even Albert Sabin, developer of the polio vaccine, understood that “a vaccine that sits on the shelf is useless.” If we want to make a dent in the epidemic, we need to find the best way to use prevention tools like PrEP today to curb the number of new infections we will need to treat tomorrow.