5/ In the same study, in 37 persons with no history of SARS or COVID-19 (negative serology and/or samples taken before COVID-19), over 50% had SARS-CoV-2 specific T cells.

This is not surprising because there are at least 4 strains of coronaviruses that cause the "common cold".

— James Todaro, MD (@JamesTodaroMD) August 10, 2020