[Lewis Thomson (OP)]

David would like an explanation as to this situation that has occured.

"I haven’t caught Covid (yet) although all of my close friends and contacts have, including my housemates. Many of my friends have caught it recently at events that I also attended and I have been pinged many times by the NHS Covid app but I have always tested negative with LFT and PCR tests. Also, my immediate family (parents and siblings) have not caught Covid. I know that have have definitely been exposed to the virus at home as well as outside of the house (bars/clubs) but I’m curious as to why. I don’t appear to be able to catch it. Is this because the vaccine (Pfizer) is working particularly well for me or do I have some underlying natural immunity and is there a test I can take to determine this?"

Leave your answers in the comments below...

[Bored chemist]

Is this because the vaccine (Pfizer) is working particularly well for me

Probably.
And luck is also a factor.

[alancalverd]

Or you had an early infection with negligible symptoms and recovered before you first tested. But "Pfizerproofing" is the most likely reason.

[evan_au]

Some people who caught SARS or MERs have been found to have antibodies that cross-react with COVID-19.

There are 4 coronaviruses which routinely infect the human population, with minor symptoms (we lump them in with "the common cold"). They tend to come back every 2 years or so, as immunity wanes. They are distantly related to COVID-19, but close enough that some antibodies cross-react with COVID-19.

PS: one of these "common cold" coronaviruses (OC43) is thought to be the pathogen behind the 1889 "Russian Flu".
https://en.wikipedia.org/wiki/Human_coronavirus_OC43

[set fair]

They tend to come back every 2 years or so, as immunity wanes.

Ye Gods.