How effective are PrEP and PEP?

How effective are PrEP and PEP

The most effective methods for preventing HIV infection are those that protect individuals from viral exposure, such as sexual abstinence, proper condom use, and avoidance of injection drug use. Unfortunately, accidents do happen and given the nature of how HIV is transmitted from one person to another, avoidance is easier said than done. In cases of potential HIV exposure, the Centers for Disease Control recommends the use pre-exposure prophylaxis (PrEP) or post-exposure prophylaxis (PEP). These preventive tools require a short course of oral antiretroviral medications to reduce the risk of HIV infection. Truvada, a combination of emtricitabine and tenofovir, was approved for prophylaxis use in the United States and other European countries, but they may not be available in other parts of the world. Truvada does not cure HIV and no other existing antiretrovirals can, but they can help lower the viral load of HIV-positive patients and prevent infection in HIV-negative individuals.

Updated guidelines


Should you take PrEP or PEP?


If you want to avoid your risk of infection in case of a future exposure à take PrEP


If you have been exposed to HIV within 72 hours and you are not on PrEP à take PEP

PrEP and PEP is not for everyone. The drugs included in the regimen is not enough to treat an existing infection, thus the course is only recommended to HIV-negative individuals. Even if you are not HIV positive, you still need to be assessed if you will benefit from the regimen. In order for these preventive methods to work, the prescribed antiretroviral regimen must be taken throughout the duration of therapy without missing a dose. With regards to the emergency treatment PEP, it is only advisable if the exposure occurs within 72 hours. It is best to seek medical help immediately, within 2–24 hours, after accidental viral exposure for better treatment outcome. You may be eligible for a PEP starter kit if you report:

  • Anal or vaginal sex without a condom with an HIV-positive partner;
  • Condomless receptive anal sex with a male or trans-female partner of unknown HIV status;
  • Sexual assault;
  • Sharing equipment while injecting drugs.

Evidence of Possible Benefits from PrEP and PEP

These preventive strategies must be carried out together with safe-sex practices to ensure successful treatment outcome. It is advisable for patients to continue the use of male or female condoms and avoid sharing drug injection equipment. If you are taking PrEP, you may be protected from HIV infection during condomless sex, but antiretroviral drugs are not 100% effective, so it’s best to err on the side of caution.

Efficacy of PrEP

Among men who have sex with men (MSM)

iPrEx Trial – 44% reduction in the risk of HIV acquisition was reported in the Truvada group. From the TDF/FTC group, 36 of 1,224 participants had acquired HIV, while 64 from the placebo group with 1,217 participants became HIV positive following treatment.

Adolescent Trial Network – There were no seroconversion observed among 68 adolescent (ages 18-22 years) participants within 24 weeks. The feasibility study compared two TDC/FTC group with and without behavioral intervention, and a third group with without treatment no behavioral intervention.

PROUD – PrEP was 86% effective in 500 MSM attending health clinics in England.

Among heterosexual men and women

Partners PrEP Trial – In a double-blind, placebo-controlled study using daily oral TDF/FTC or TDF alone for preventing HIV infection in discordant heterosexual couples in Uganda and Kenya, TDF was 64% effective while the combination of TDF/FTC was 75% effective.

Among individuals who inject drugs

Bangkok Tenofovir Study – With daily oral TDF, there was a 73.5% reduction of HIV acquisition among injection drug users.

Efficacy of PEP

Before extending PEP to non-occupational high-risk patients, it has been used for many years as emergency prevention for healthcare workers, including those who have accidentally pricked themselves with needles used on people who were known HIV-positive. There were no randomized, placebo-controlled trials conducted to test the effectiveness of PEP for non-occupational exposure, but there are available perinatal trials, animal transmission models, and observational case studies that warrant the efficacy of PEP for preventing HIV infection after an exposure.

PEP studies – In using zidovudine as PEP among healthcare workers with percutaneous exposure to HIV, there was 81% reduction in HIV acquisition.

Sexual assault review – Using data from 3 systematic reviews and 1 cohort study spanning various age groups from childhood to adulthood, wherein 4% to 100% sexual assault victims accepted PEP, no HIV screening results or non-occupational PEP failures have been documented.

Disclaimer: Please note that the contents of this article are for informational purposes only and should not be considered medical advice. This article, and other AIDS and HIV Information articles on AIDS Drugs Online, are not written by AIDS Drugs Online or reviewed by its staff for medical validity. All views and opinions expressed by the third-party authors are not endorsed by AIDS Drugs Online or its staff. Always consult a medical professional for medical advice.


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