Top 5 HIV PrEP stories from CROI 2024

Dr Brenda Mirembe, lead researcher on the INSIGHT PrEP study, at CROI 2024. Photo by Roger Pebody.
Dr Brenda Mirembe, lead researcher on the INSIGHT PrEP study, at CROI 2024. Photo by Roger Pebody.

One of the most important HIV conferences of the year, the Conference on Retroviruses and Opportunistic Infections (CROI 2024), took place earlier this month. Here are some highlights from research on PrEP (regular medication to prevent HIV) presented at CROI.

A 79% reduction in HIV incidence was seen between two directly comparable groups in a whole-population analysis of people using PrEP in Australia. While we know that PrEP is highly effective at preventing HIV at an individual level, its effectiveness as an intervention is harder to measure at a population level. Researchers used dispensing data to estimate the number of new HIV diagnoses among people who regularly took PrEP between 2018 and 2023, compared to those who only had one PrEP prescription filled during the same period. Compared to people who only received PrEP once, incidence was 79% lower in the group that was more adherent (with PrEP coverage over 60% of the time).


post-exposure prophylaxis (PEP)

A month-long course of antiretroviral medicines taken after exposure or possible exposure to HIV, to reduce the risk of acquiring HIV.

event driven

In relation to pre-exposure prophylaxis (PrEP), this dosing schedule involves taking PrEP just before and after having sex. It is an alternative to daily dosing that is only recommended for people having anal sex, not vaginal sex. A double dose of PrEP should be taken 2-24 hours before anticipated sex, and then, if sex happens, additional pills 24 hours and 48 hours after the double dose. In the event of sex on several days in a row, one pill should be taken each day until 48 hours after the last sexual intercourse.


Refers to the mouth, for example a medicine taken by mouth.


An umbrella term for people whose gender identity and/or gender expression differs from the sex they were assigned at birth.

cisgender (cis)

A person whose gender identity and expression matches the biological sex they were assigned when they were born. A cisgender person is not transgender.

Research in rural Kenya and Uganda has shown the added benefits of offering a choice between PrEP pills and PrEP injections. The programme had already demonstrated that a dynamic, person-centred HIV prevention intervention results in substantial increases in the numbers of people covered by PrEP or PEP. When services were offered in the usual way, a minority of people used oral PrEP or PEP. When services were optimised to provide choice and flexibility, uptake more than doubled.

In the latest stage of the randomised study – with the additional option of PrEP injections – 70% of people used some form of biomedical HIV prevention. Notably, of those who started injectable PrEP at the beginning of the study, 42% hadn’t been using any form of HIV prevention in the month before.

A study conducted in six African countries with high HIV prevalence, achieved high levels of oral PrEP uptake and persistence, and good levels of adherence among its 3000 young female participants. The INSIGHT PrEP study is working at 14 sites in South Africa and one site each in Eswatini, Kenya, Malawi, Uganda and Zambia. Data were collected between August 2022 and August 2023, though follow-up time for each individual was six months. Uptake and persistence with PrEP was shown to be good, with 92% of participants completing all four study visits and 90% receiving every refill of PrEP. Drug level monitoring for some participants indicated recent adherence of around 70%. This level of adherence is better than that seen in most previous studies with African women, but 1.4% of participants still acquired HIV.

Services providing PEP (emergency medication to prevent HIV) and PrEP need to build stronger connections between these two ways of preventing HIV, to help people who have used one method to access the other, according to experts at CROI. Overall numbers of people seeking PEP are low, but in recent years many of those accessing it have previously been prescribed PrEP. In the US, separate guidelines are issued for each prevention method, and they do not emphasise linkages between them.

In the UK, guidelines recommend a smooth transition from PEP to PrEP and at 56 Dean Street, a large clinic in London, everyone receiving PEP is offered a one-month supply of PrEP, to be started when they complete the 28-day course of PEP. Research presented at CROI showed that three-quarters of people prescribed PEP accepted the offer of PrEP.

At CROI 2024, aidsmap's Krishen Samuel spoke to Dr Jenell Stewart about event-based PrEP.

In a symposium on PrEP, Dr Jenell Stewart argued that event-driven PrEP is as effective as daily PrEP for gay men and trans women, and that it could also work just as well for women and others who have vaginal sex. Event-driven PrEP means taking PrEP only around the time of a possible exposure to HIV, rather than daily. Most guidelines support event-driven PrEP as an option for gay and bisexual men and trans women, but not for cisgender women. Stewart argued that event-driven PrEP for women should be reconsidered and researched further.