Interesting but long paper exploring cross reactivity of other infectious agents including seasonal coronaviruses on increasing immunity among health care workers.
Pre-existing polymerase-specific T cells expand in abortive seronegative SARS-CoV-2
https://www.nature.com/articles/s415..._reference.pdf
I wonder if any studies have been done among other groups such as teachers that are exposed frequently? Might be interesting to see if Covid-19 incidence impacts different professions more than others.