To date, just four cases of possible PrEP failure have been reported in the medical literature or at scientific conferences.
Officials with Public Health — Seattle & King County report a rare case of newly diagnosed HIV infection found to have a virus resistant to both of the medications in the Truvada pill in a King County man.
Director of Public Health’s STD/HIV program, Matthew Golden, MD said the patient likely became HIV infected while taking PrEP. The man reported sex only with other men, and both he and his medical provider indicated that he had consistently taken daily PrEP in the months since his last HIV negative test and prior to testing HIV positive.
Truvada as HIV PrEP is very effective if taken consistently. It reduces the risk of acquiring HIV through sex by over 90%, and perhaps by over 95%. It is also more than 70% effective in preventing HIV infections transmitted through sharing injection equipment. So while it is very effective, like many drugs, it is not 100% effective.