What is the efficacy of HIV postexposure prophylaxis (PEP)?

Updated: Jul 08, 2021
  • Author: Derek T Larson, DO; Chief Editor: Michael Stuart Bronze, MD  more...
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Postexposure prophylaxis for non-occupational HIV exposures remains controversial. Comparatively, HIV PEP following occupational exposures has been shown to reduce risk of transmission by around 80%. [6]  It is unclear whether PEP is effective in preventing seroconversion after non-occupational exposure to HIV. Justification of the efficacy, timing, and duration of nPEP has been extrapolated from 4 lines of evidence, as follows:

PEP is not 100% effective. PEP failures are more likely to be associated with zidovudine monotherapy, [16, 20, 21] infections with HIV strains that are resistant to the antiretroviral medications, [22] and ongoing exposures to HIV. [19, 22, 23, 24, 23] In patients who seroconvert despite nPEP, resistance testing should be strongly considered to guide early and subsequent treatment decisions.

Despite this, outcomes are typically good, as per-act risk of HIV acquisition remains low. For reference, a needlestick from an HIV-infected source leads to seroconversion in only 1 of 435 percutaneously exposed healthcare workers, and a single act of receptive penile-vaginal intercourse leads to infection in 1 of 125 instances. [1]  Receptive anal intercourse remains a higher risk, at 1 of 73 instances. [1]  Studies have shown that the odds of seroconversion were 0.04% for female-to-male transmission and 0.08% for male-to-female transmission per penile-vaginal sexual act in higer resource settings and demonstrated a transmission rate of 0.38% and 0.30% for female-to-male and male-to-female transmission, respectively, in resouce-poor settings. [25]  

Extensive scientific progress has been made in understanding factors effecting the risk of disease transmission, one of those findings is that viral load is a key determinant of transmission risk. [4]  If the source patient is known to have HIV infection but is virologically controlled on medication, the risk for sexual transmission has been shown to be negligible. [26, 27]  Following the results of HPTN 052, [4] multiple large studies [28, 26] have confirmed these findings and established that Undetectable = Untransmittable (U=U), and subsequently led to a national education campaign regarding the success of treatment as prophylaxis against HIV transmission.

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