PrEP policies should be based on the specifics of local epidemiology so that PrEP reaches individuals who are most likely to benefit from it – those who are at elevated risk of acquiring HIV and are also able to achieve good adherence.

For gay men, several studies have identified behaviours strongly associated with acquiring HIV, and these can be used to guide PrEP policies. Less is known about adherence, but in some studies it has been better in individuals at greater risk of HIV. PrEP could be offered to men recently diagnosed with a sexually transmitted infection, or reporting receptive anal intercourse without a condom, or higher partner numbers. Other factors, such as recent use of post-exposure prophylaxis (PEP) or chemsex (sexualised drug use) might also be relevant.

While individuals who have HIV-positive sexual partners might appear to be ideal candidates for PrEP, they may have a relatively low risk of infection if their partner is on treatment and has an undetectable viral load. But people’s relationships can change rapidly – methods for identifying individuals who could benefit from PrEP need to focus on current factors and be sensitive to the way in which people go in and out of risky behaviour.

Based on studies with heterosexual couples of different HIV statuses in African countries, researchers developed a risk assessment tool to identify the HIV-negative partners at greatest risk of acquiring HIV. This takes into account younger age, a high viral load, having sex without a condom, living together, not having children and circumcision status (if the man is HIV-negative).

As our understanding of the behaviours associated with HIV acquisition in heterosexual adults in the UK is less well developed, it may be challenging to define criteria for PrEP provision for heterosexuals. Decisions may need to be made on a case-by-case basis.

A draft position statement from BASHH and BHIVA states: “BASHH and BHIVA strongly recommend that PrEP be made available within a comprehensive HIV prevention package to MSM who are engaging in condomless anal sex, and to HIV negative partners who are in serodiscordant heterosexual and same sex relationships with a HIV positive partner whose viral replication is not suppressed.”

While PrEP may have significant benefits for some individuals, this doesn’t necessarily mean that it will bring an end to the HIV epidemic. If demand for PrEP is low and relatively few people take it, or if health services find it difficult to identify and engage individuals at greatest risk of infection, PrEP may only make a small dent in the number of new infections. If the availability of PrEP leads to fewer people using condoms, then this could offset the benefits of PrEP. If uptake is overly concentrated in some demographic groups, it may deepen health inequalities.