Pre-exposure prophylactic treatment (PrEP) for HIV is commonly said to reduce infection rates by more than 75%.

Similar treatments for already-infected patient treatments do not cure HIV, but reduce viral load to undetectable levels. If treatment of these patients is stopped, viral load will eventually rise.

Do we know that PrEP actually prevents infection, rather than masking it? Are there no cases of someone engaging in no risk behaviors, then going on PrEP and engaging in risk behaviors, then coming off it, not engaging in any further risk behaviors, and nevertheless testing positive for HIV?

  • $\begingroup$ "Are there no cases of someone being on PrEP, coming off it, and then testing positive for HIV?" is absolutely the wrong question to ask and is not how scientific study works, but everything else here is a good question. $\endgroup$ – Bryan Krause Mar 30 '18 at 15:41
  • $\begingroup$ Edited to improve last section $\endgroup$ – DJG Mar 30 '18 at 15:45
  • $\begingroup$ Still bad. Asking "are there no cases" implies that if you saw one case, you would conclude it's a masking effect. That's wrong, especially in light of the previous claim which is a 75% reduction: clearly there are still cases that PrEP does not prevent. Furthermore, not "engaging in any further risk behaviors" is an impossible thing to ask for in a clinical trial. You would have absolutely know way to know if there is a masking effect or if people are just lying about not engaging in further risk behaviors. $\endgroup$ – Bryan Krause Mar 30 '18 at 15:46

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