This is JUST an example of some of the unknowns we are up against with this particular virus. This is a post from someone in VETERINARY medicine, I stress. I am NOT saying this applies to this novel coronavirus circulating in humans. I simply point it how to show how complex this shit can be. Post as follows, from the Ars forums:
In my field, (Veterinary medicine) we have some experience with reinfections with coronaviruses, some of which are associated with rapid mutation, and some of these can lead to quite catastrophic complications.
Coronaviruses are responsible for a reasonable number of acute gastrointestinal upsets in both dogs and cats. The coronavirus that affects dogs was, for a long time, considered pretty benign. In recent times, however, we are seeing a more aggressive presentation with systemic spread as well as GI signs. We tend to see canine enteric coronavirus in local epidemics, and my (subjective) impression is that the dogs are only infected once, we usually see it in younger dogs.
Canine Enteric Coronaviruses: Emerging Viral Pathogens with Distinct Recombinant Spike Proteins
Canine enteric coronavirus is an alpha-coronavirus. There is also a canine respiratory coronavirus which is from the beta-coronavirus group, the same group as SARS-CoV-2. The canine respiratory coronavirus is generally associated with mild clinical signs in most dogs, and is most commonly associated with close contact situations such as housing in boarding kennels.
The canine coronaviruses are probably a good model of what we hope SARS-CoV-2 will be like. The feline coronavirus, though, is decidedly more creepy.
Cats have an enteric coronavirus (FECV) that can establish a persistent gastrointestinal infection, and is associated with very mild GI signs. FECV is an alpha-coronavirus, like the canine enteric virus. The cats do not establish immunity to FECV, and in multi-cat environments (catteries, multi-cat households, shelters) there tends to be persistent transmission from cat to cat within the group. While this is pretty benign, with each round of infection there is a chance that the FECV will mutate to a much more unpleasant virus: Feline Infectious Peritonitis.
I'm grossly simplifying the following
When the FECV mutates to FIP, it sets up a persistent infection within macrophages. The cat's immune system does respond to the FIP virus, but the virus is protected from antibody binding by being within the macrophages. The cat's immune system just churns out antibodies, and this can lead to accumulation of large volumes of very high protein fluid in body spaces (abdominal cavity, chest cavity, even the central nervous system). In some cats, instead of an antibody mediated response resulting in high protein fluid accumulation, they have a runaway cell-mediated response, resulting in granuloma formation in affected organs. We call this "dry form FIP".
We currently consider FIP, in either wet or dry form, to be almost invariably terminal in cats. There is some evidence that newer viral protease inhibitors and a nucleoside analog can be beneficial, these are years away from regular use and availability.
The thing that haunts my dreams is the thought that the SARS-CoV-2 could mutate in a manner that leads to long term complications similar to FIP. I keep telling myself that SARS-CoV-2 is an alpha, not a beta, but there is a part of my mind that is just waiting for a nasty rash of horrible, long term autoimmune inflammatory disease in humans that have 'recovered' from SARS-CoV-2.