The study, conducted by the Kenya Medical Research Institute, looked at female sex workers (FSW) and men who have sex with men (MSM) in the Kenyan cities of Mombasa and Nairobi. Seventy-two participants between ages 18 and 46 were enrolled, and 51 were assessed following a four-month randomized, placebo-controlled, blinded trial that compared daily and intermittent dosage of PrEP.
Published in the medical journal AIDS and Behavior, the study found that adherence was significantly higher – 84 percent – among those who took the daily dose compared to participants in the groups that took the drugs intermittently before sex, 68 percent of whom adhered to the PrEP course, and those on a fixed intermittent dose, 26 percent of whom adhered.
The investigators found that side-effects "were experienced early in the study but diminished over time".
"Given the severity of the epidemic [among] key populations – including men who have sex with men, men who have sex with men sex workers and female sex workers – and… the scarcity of services, the results of the PrEP study present a promising means of protecting sero-negative [HIV-negative] MSM and FSW from acquiring HIV from partners of either sex," Elisabeth Vanderelst, lead researcher for the study, told IRIN/PlusNews in an email.
"High-risk populations are in dire need of strategies – other than condoms – that prevent HIV transmission, especially sex workers," she added.
According to the 2009 report Kenya: HIV Prevention Response and Modes of Transmission Analysis, commercial sex workers and their clients together contribute 14 percent of all new HIV infections, while MSM and prisoners account for 15.2 percent.
According to a 2012 survey by the National AIDS and Sexually Transmitted Infections Control Programme, the World Bank, Kenya Prisons and Canada’s University of Manitoba, there are an estimated 200,000 commercial sex workers in Kenya, 15,000 of whom are men.
Participants also helped researchers improve PrEP administration. "Suggestions for tablet improvement were made by study participants, and an important one [was] taken forward by the pharmaceutical industry, i.e., the development of a so-called ‘slow release’ jab to replace the Truvada [a type of ARV] tablet," Vanderelst said.
The study also found a high prevalence of social issues related to being perceived as HIV-positive, such as stigma, gossip and problems in relationships.
Alcohol use around the time of sex was found to have an effect on adherence to the ARVs after sex; 47 percent of participants reported drinking alcohol before sex. Movement from place to place and transactional sex work also affected PrEP adherence.
The authors recommended "culturally appropriate and consistent counselling" to address these issues and ensure PrEP effectiveness.
Vanderelst said that, while the study provided some useful insights, more evidence would be necessary "to guide expansion of comprehensive HIV prevention for key populations in sub-Saharan Africa".
In July, the UN World Health Organization (WHO) issued guidance to governments on the use of PrEP, calling for a cautious and gradual roll-out.
Evidence for the effectiveness of PrEP comes from clinical trials on the daily use of ARVs for HIV prevention among high-risk HIV-negative people. A 2010 study, Iniciativa Profilaxis Preexposicion (iPrEX), among MSM and transgender people found that a daily dose of Truvada – a combination of emtricitabine and tenofovir disoproxil fumarate – reduced HIV infection risk by about 42 percent.
The 2011 Partners PrEP study in Kenya and Uganda concluded that a daily dose of Truvada taken by an HIV-negative partner in a heterosexual relationship with an HIV-positive partner could reduce the risk of HIV transmission by up to 75 percent.