Hi, I checked the forum and couldn't find an answer to this, so apologies in advance if this question has already been answered. My question is: I'm on PrEP and I catch HIV because for example I do not follow the scheme properly thus I'm not protected. I then have sex with somebody else who is also on PrEP, will I run the risk to pass HIV on to this person? Will my HIV be resistant to PrEP or will the other person be protected by his PrEP? Thanks in advance for your answer and I hope I was clear enough and apologies if this is a stupid question.


Thank you for writing in. There are no stupid questions in education, and I'm grateful that you and so many others trust the The Body as a valued resource. And you are right this question hasn't been asked exactly this way in the forum before.

So let's start with the premise - What if you get HIV while on PrEP? Well, we do know that is exceedingly rare given there are only two documented cases in the world of someone acquiring HIV with verified adherence to PrEP ( That means PrEP reduces the possibility of acquiring HIV by much more than 99%.

But as you point out, if someone does not adhere to their scheme, they increase the possibility of acquiring HIV. I do want to direct your attention however, to the science which tells us that after a month of daily PrEP one still has a significant amount of protection for rectal sex a week after stopping ( One need not follow the scheme perfectly in order to have significant protection from HIV.

If someone on PrEP becomes HIV positive and then continues to take the drug (Truvada, or its generic equivalent), then their stain of HIV might build resistance to the medications in Truvada, called emtricitabine and tenofovir disoproxil fumarate. That is why it is so important that anyone who is using PrEP receive regular HIV testing, approximately every three months or so.

If your partner is using PrEP as prescribed,then he would still have the full protection afforded from using PrEP even if you were HIV positive, not in treatment, with a resistant strain, with a detectable viral load. PrEP protects the person who is using it from HIV. That includes resistant detectable strains of HIV.

The reason why people question this is because one of the two cases I mentioned above, where a person acquired HIV with full adherence to PrEP, did acquire a strain of HIV that was resistant to several medications. Truvada did not protect him from the strain of HIV. After this was reported in 2015 we thought we'd see more cases like this - where daily Truvada would fail to protect someone from resistant strains of HIV. But so far that has not been the case. We have no way of measuring how often PrEP protects from these resistant strains, we just know that that there is only one case where this actually happened with verified adherence.

In other words, it is EXTREMELY unlikely that you would acquire HIV while on PrEP. Even less likely you would develop a resistant strain if you were getting tested regularly. But if that were to happen, your sexual partners would still have the full protection afforded by PrEP as long as they were using it as prescribed.

For more information about PrEP and real world experiences from around the globe, please feel free to join my "PrEP Facts" group on Facebook: .

To see updated information about reports of people acquiring HIV while on PrEP, please visit our database here at The Body: