High adherence to HIV prophylaxis may raise efficacy for couples where one partner has HIV

The study, which was led by Jessica Haberer, from Harvard Medical School, Boston, United States, included 1,147 HIV-uninfected participants who were enrolled in three Ugandan sites of the Partners PrEP Study- a randomized controlled trial to determine efficacy and safety of PrEP. All participants had a partner who was HIV-positive. These participants were a convenience sample reflecting 66% of all participants in the study sites (they were not randomized as part of this substudy). They were actively monitored for adherence to antiretroviral drugs and received adherence counselling throughout the study, which was intensified if unannounced pill count adherence fell below 80%.

Several randomized controlled trials in various populations (i.e. men who have sex with men, women at high risk for HIV) have shown that PrEP has provided varying levels of protection against HIV infection. One possible explanation for this varying efficacy is differential adherence to the antiretroviral drugs. Within this substudy, where adherence to antiretroviral drugs was very high (99% by unannounced pill counts and 97% by electronic monitoring), only 14 individuals became HIV-positive during an average follow up of 11 months per participant, and all of these individuals were taking a placebo drug.

Although the study has some limitations, such as the non-randomized nature of the study and limitations inherent in any form of adherence monitoring, the findings indicate that the high level of PrEP adherence achieved in the setting of active adherence monitoring and counselling support was associated with a high level of protection from HIV acquisition by the HIV-uninfected partner in heterosexual serodiscordant couples.

The authors note, "These data provide further support that PrEP is highly efficacious at preventing HIV acquisition when it is taken."

The authors conclude, "Proper support and assessment of adherence will be critical for determining efficacy of PrEP outside of clinical trials. This data will be important for guiding ethical decisions about resource allocation for both prevention and treatment of HIV."