As Dr. Tremblay just said, there are still so many unknowns around this virus. We know there is an antibody response, but we don't know how long that will last. If you were to look at the last rapid-response COVID-19 CIHR grant, you'd find a couple of people putting that particular question in so that we are able to actually have an answer to it.
Again, as Dr. Tremblay said, most of the people we've seen with relapse, positive PCR, were likely the same patients with undetectable PCR who became positive again. We had a patient like that. They were positive for 65 days, with one bit in between that was negative and where the virus never grew.
We're not exactly sure why this virus hangs around for so long, but it does. It doesn't mean people are still infectious, though.