Adhering to the daily dosing schedule of pre-exposure prophylaxis is fundamental to PrEP's success at preventing the acquisition of HIV, aidsmap reports. Publishing their findings in the Journal of Acquired Immune Deficiency Syndromes, investigators in the Partners PrEP study drew a cohort from a pool of 4,747 men and women in Kenya and Uganda who had a partner living with HIV and who were given either Truvada, which contains tenofovir and emtricitabine, or just tenofovir, as PrEP. The cohort included 29 people who contracted HIV during the study and 196 randomly selected participants who remained HIV negative and who served as controls.

Seventy-one percent of the controls had tenofovir levels that indicated they were taking PrEP daily, compared with just 32 percent of those who seroconverted. Counts of the pills the participants took indicated that 96 percent of the controls adhered at a rate greater than 80 percent, compared with 65 percent of the seroconverters. Five out of 29 (17 percent) of those who contracted HIV appeared to take PrEP consistently.

The researchers estimated that daily use of Truvada reduced the risk of contracting HIV by 91 percent, and that tenofovir on its own reduced the risk by 89 percent.

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To read the study abstract, click here.