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Event-driven HIV prevention regimens appeared to have a better protective effect, and a better trend of medication adherence, than daily regimens in a real-world setting among men who have sex with men (MSM), a researcher said.

In four cities in China, MSM who opted for event-driven pre-exposure prophylaxis (PrEP) -- that is, that they only took the medication before and after sex -- had fewer HIV infections compared with daily PrEP users (two vs five, respectively), reported Junjie Xu, PhD, of China Medical University in Shenyang.

The proportion with anal sex acts covered by PrEP at least 90% of the time increased over the 12-month follow-up period in event-driven users (57.4% at month 1 vs 77.8% at month 12, P=0.022 for trend), while declining among daily users (75.1% at month 1 vs 72.1% at month 12, P<0.001 for trend), according to a late-breaking presentation at the virtual International AIDS Society Conference on HIV Science.

Event-driven PrEP is defined as taking two pills from 2 to 24 hours prior to sex, one pill 24 hours after that, and another 24 hours later (the 2+1+1 schedule). If sex acts take place on consecutive days, one pill should be taken every day until 48 hours after the last sex act. While the World Health Organization (WHO) updated its HIV prevention guidelines in 2019 to include event-driven PrEP, CDC currently for high-risk individuals.

Xu noted that China contributed the largest proportion (29%) of new HIV infections in the Asia-Pacific region in 2018, with infections among MSM rising from 14.7% in 2011 to 23.3% in 2018.

However, until the beginning of this study, PrEP was not approved in China for HIV prevention due to "lack of local high quality data to support widespread implementation," he said.

"As a result of evidence from our study, an expert consensus was issued to guide PrEP implementation at the end of 2020," Xu added.

His group performed the China Real-world Orally intake PrEP (CROPrEP) study in four Chinese cities from December 2018 to October 2020. Tenofovir disoproxil fumarate/emtricitabine (TDF/FTC, or Truvada) was offered to MSM, who were allowed to choose between daily or event-driven PrEP regimens. At-risk MSM who were unwilling to initiate PrEP acted as a control group. The authors followed up with participants every 3 months, up through 12 months.

Overall, 520 MSM selected a daily regimen, 503 selected an event-driven regimen, and 507 declined to initiate PrEP. Those initiating PrEP were younger than non-users (age 29 vs 33, respectively) and had higher scores for risk behaviors.

During the follow-up period, all PrEP users had a relative reduction of 87% in HIV infection, while adherent PrEP users had 100% risk reduction. Xu noted all seven seroconversions in the PrEP group were among non-adherent users.

Incidence rate of HIV infection was lowest among event-driven PrEP users (0.37 per 100 person-years), followed by daily PrEP users (0.90 per 100 person-years), and was unsurprisingly higher among PrEP non-users (5.10 per 100 person-years).

Xu concluded that the study showed PrEP can reduce HIV risk among MSM in a real-world setting, with event-driven PrEP offering "a better HIV protective effect."

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