In addition, the study, which was financed by the German Federal Ministry of Education and Research's special funding line COVID-19, analyzed donor blood samples which were collected before the outbreak of the pandemic and thus had no contact with SARS-CoV-2. Strikingly, small amounts of SARS-CoV-2-directed T-cells, which recognize virus components, were identified in 81 percent of these unexposed donors.
This could be due to previous contact of the donors with other human common cold corona viruses (HCoV-OC43, HCoV-229E, HCoV-NL63 and HCoV- HKU1) and sequence similarities of the SARS-CoV-2 T-cell epitopes with these HCoVs.
However, such cross-reactive T-cell detection is not equivalent to immunity against SARS-CoV-2: "The effect these preexisting cross-reactive SARS-CoV-2 T-cell responses in 81 percent of the population will be investigated further prospective studies," commented Juliane Walz.
