Several months after infection with SARS-CoV-2, some patients still have symptoms: a phenomenon commonly referred to as "long COVID". Teams from Inserm and Université Paris Cité, in collaboration with the University of Minho in Braga (Portugal), have shown that this could be explained biologically by abnormalities of the immune system associated with the persistence of the virus in the mucous membranes.
It’s quite plausible, the fact that it never really clears from the system is pretty concerning.