The effect of using post-exposure prophylaxis to lower transmission risk

Post-exposure prophylaxis (PEP) is a short course of HIV medication, usually a combination of two or three drugs, that is prescribed for 28 days. The purpose of PEP is to prevent the small amount of HIV that may have entered the body from taking over enough cells to establish lasting infection.

PEP was first used by healthcare workers. In certain settings, most commonly in high-income countries, access has been expanded to other people who may be exposed to HIV occupationally. In some settings, PEP is also recommended for people with probable non-occupational exposure to HIV as a result of sexual assault, condom failure or unprotected sex.

Two key studies have provided evidence that PEP can prevent HIV infection: one study showed that antiretrovirals prevented monkeys from being infected with a virus similar to HIV, known as SIV (simian immunodeficiency virus); and a second study found that a single antiretroviral taken within 24 hours of needlestick exposure reduced the risk of HIV infection among healthcare workers by 80%.¹ For ethical and practical reasons, it is not feasible to conduct a randomised trial that might provide stronger evidence of PEP’s effectiveness.