Don’t remember the study but pretty sure that cross reactivity thesis to common cold eventually didn’t pan out. Believe Derek Lowe wrote about it.
> Now, you can still make an argument that the T cell component of immunity might provide some protection after a previous coronavirus infection. The current study didn’t address this directly
Lowe's July 2020 article on T-cells, https://blogs.sciencemag.org/pipeline/archives/2020/07/15/ne...
> there are, in fact, people who have both CD4+ and CD8+ T cells that recognize protein antigens from the new coronavirus even though they have never been exposed to SARS, MERS, or the new virus. The paper speculated that this might be due to cross-reactivity with proteins from the “common cold” coronaviruses”, and raised the possibility that there might be a part of the population that has at least some existing protection against the current pandemic.
and
> patients who had caught SARS back in 2003 and recovered ... still have (17 years later!) a robust T-cell response to the original SARS coronavirus’s N protein ..This new work finds that these cross-react with the new SARS CoV-2 N protein as well
There is an open question in the Nature study, about prior, unknown animal coronaviruses which may have previously infected humans and conferred T-cell protection against SARS-CoV-2.
> But here’s the key part: “cross-react” does not mean “neutralize” and it does not mean “provide protection from”. These antibodies may or may not have been neutralizing against the other coronaviruses, but they don’t seem to have any such effect on the current one. And in keeping with that, having such cross-reactive antibodies seems to provide no protection against catching SARS-Cov2 or against being hospitalized with it if you do. There’s no difference in the infection/hospitalization rates of the people who had cross-reactive coronavirus serum antibodies ready to go versus those who didn’t. They’re basically useless.
> Now, you can still make an argument that the T cell component of immunity might provide some protection after a previous coronavirus infection. The current study didn’t address this directly, but after these results, it’s at least less likely that that’s happening. The authors make a note of this, and also note that pre-existing mucosal antibodies might exert a protective effect (which this study didn’t examine, either). But prior circulating human coronavirus antibodies, even ones that can bind to the current one – those it looks like we can rule out. Which is too bad.
It's interesting that your comment omitted:
> The current study didn’t address this directly, but after these results, it’s at least less likely that that’s happening.
Why is that?