Here is a summary of at least 6 articles on pre existing t-cell immunity. https://www.bmj.com/content/370/bmj.m3563

Furthermore, I know of at least 3 leading statisticians that hypothesized (very early on) that the variance of infection trends pointed to pre-existing immunity in various populations. The evidence supporting this is mounting.

The BMJ is not a credible source, it is the Daily Mail of medical journals. The author of that article, Peter Doshi, has form:

"I think the first thing we to review is who is Peter Doshi? And why is he so insistent on getting this data?

Peter Doshi received his BA in anthropology from Brown University, MA in East Asian studies from Harvard University, and Ph.D. in history, anthropology, and science, technology and society from the Massachusetts Institute of Technology. Those would be fine credentials for someone who is going to teach history or anthropology."

https://www.skepticalraptor.com/skepticalraptorblog.php/pete...

I didn't cite the BMJ as the source, but nice try. The sources include Cell and Nature, but unfortunately for you that might mean having to read something in order to discount it, which you seem unprepared for.

There is a more balanced review article on herd immunity here: https://www.nature.com/articles/d41586-020-02948-4

For the lazy (cited 556 times as of now): https://www.cell.com/cell/pdf/S0092-8674(20)30610-3.pdf

That paper looks at 40 people and has no idea what the clinical correlates of the non-spike responses are because no one has any idea. You cannot take that paper and say that a substantial factor of people are protected due to preexisting responses.

There's at least another paper detailing this phenomenon[1] so for sure it warrants further investigation.

[1] https://www.nature.com/articles/s41590-020-00808-x