And aren't there others that look at other parts of the immune system like T-cells and such? I think those are just being done in research studies and aren't commercially available.

Everyone we know personally in the UK has had Covid, except my younger sister. She was classed as vulnerable, so was vaccinated early and has been extremely careful with contacts, working mostly from home.

Some like our daughters had no symptoms whatsoever, most like me had a few days resting in bed coughing and a week or more recovering. One NHS worked had long Covid taking over half a year to return to near full strength.

Two people we know in their 60's we know well and who refused vaccinations, had fairly minor Covid symptoms, both feeling grotty with a bit of a cough and cold for a week.

Only one person I know has died, he worked in a shop/cafe we frequented in London and was classed as vulnerable, being diabetic in his late 60's.

I'm guessing pretty much everbody who lives, travels & works in a large city will have been exposed to Covid.