A reader writes:
I'm a loyal reader and a grad student in public health with an interest in HIV/AIDS, so your posts on Truvada prophylaxis caught my attention. Good news? Yes. Breakthrough? Not so fast. First off, the 44 percent figure is the important one - not 90 percent - because what really matters is how well the drug works in real life. That a large percentage of the participants in this study still didn't take the pills regularly despite having better-than-average medical attention is a serious problem. Also, all study participants received HIV testing, safe sex counseling, condoms, and treatment for STIs during the study. Who knows whether the effect would be as strong with people not receiving all those other protective services - could be higher or lower.
But the biggest red flag to me is behavioral disinhibition, the idea that people act differently when they believe their risk is lower.
A benefit from a 44 percent decrease in infections could quite easily be eliminated by changes in sexual behavior that would result from the knowledge that you're "protected." That's also a huge worry re: male circumcision, which is being pushed in sub-Saharan Africa right now. Studies suggest that circumcision does have a protective effect, but it remains to be seen whether that will hold true on a population scale when men believe it protects them and thus may change their behavior. The circumcision studies, like the Truvada study, were all done with intensive counseling (for ethical reasons) which makes the results far less generalizable. The way circumcision is being pushed in areas with high HIV prevalence is, to me, a quite frightening population-wide experiment, because we just don't know yet whether it will help or hurt.
Yes, the Truvada study is big news, but we'll need a lot more data before we'll know if it's really a breakthrough.
All of this is perfectly true, for the population as a whole. We will indeed see if this good news is a breakthrough. But compliance with drug regimens is always an issue - and a single pill is arguably the simplest, easiest regimen to follow. Perhaps, taking a pill to prevent infection rather than treat it makes it more likely to be missed or followed intermittently - but even then, the danger of failure is much less than with highly complex, multi-drug post-infection regimens.
The core point for me is that if one person diligently takes this drug and has a sex life, he or she is far, far less likely ever to become infected. We have never been able to say that in the three decades we have lived with this disease in America. That's why it's a breakthrough. And given the success of complex drug regimens in Africa and in poor, urban America, I see no reason not to be optimistic about a simple prophylaxis like this - especially for women who cannot get their lovers to wear a condom.