HIV/AIDS activists are reminding New York City’s gay community to continue using condoms even while taking the HIV-prevention pill Truvada, as a rare new strain of drug-resistant HIV has infected two men since February.

The most recent case of a man contracting HIV while on PrEP was announced by Cleveland Clinic HIV specialist Howard Grossman on Tuesday, Buzzfeed reports.

According to Grossman, the patient is a gay man in a long-term relationship with an HIV-positive partner.

Despite having taken Truvada since January, being the “receptive partner,” and having “the appropriate blood levels of the pill’s two drugs — tenofovir and emtricitabine — to offer the nearly 99% protection it offers from the virus,” the patient became HIV-positive after he and his partner had unprotected sex with a third person on two occasions and with two different people.

Buzzfeed’s Azeen Ghorayshi reports the patient’s “new strain did not match his partner’s, meaning that the multi-drug-resistant virus must have been transmitted during one of the two sexual encounters.”

While PrEP advocates still urge users to protect themselves from HIV by using Truvada and condoms together, POZ magazine’s Benjamin Ryan said “the fact that there have been only two documented cases of PrEP failure so far underlines the strong likelihood that such cases will remain very rare.”

Sharing that sentiment, Grossman told Ryan: “PrEP works and is the most successful intervention we have had; failures have been vanishingly rare, and that’s not changing; and tops can get infected.”