T-cell immunity seems to be important in respiratory virus infections in general, including SARS. This paper is from 2018:
The CD8 T Cell Response to Respiratory Virus Infections
This excerpt from the text speaks to the cross-protection of different strains:
...robust memory CD8 T cell responses efficiently reduced lung viral titers in the absence of neutralizing antibodies following RSV, IAV, or SARS secondary infections. An important property of CD8 T cells is that they often recognize conserved viral proteins, allowing for cross-protection between different virus strains.
So, it's possible that people who have been previously exposed to a similar coronavirus might have a much better immune response to COVID-19.
I’m 66 years old, now; and in young to early-adult life, I seemed to catch everything that was going around. Over the past 30 years, I haven’t caught much at all - except in late 2017, when my boss flew back from Mexico with an illness, and seemed to transfer to me the longest fever and most debilitating ‘flu that I’ve ever experienced.
If I survived that, I can probably survive this - whatever it is. I’m not going out and inviting it; but I’m not allowing myself to be afraid, or enclosing myself in bubble-wrap, either.
I have no problem with going to the grocery store or pharmacy; and I’d have no problem with going to my local polling location and VOTING.