“Previous studies have reported that 20–50% of people who hadn’t been exposed to SARS-CoV-2 showed T cell responses against different parts of the SARS-CoV-2 virus. To investigate further, a research team led by Drs. Alessandro Sette and Daniela Weiskopf at the La Jolla Institute for Immunology tested blood samples collected between March 2015 and March 2018 for T-cell responses against different pieces of SARS-CoV-2…
[The researchers] found that of the SARS-CoV-2 and ‘common cold’ coronavirus fragments that were most similar (at least 67% genetic similarity) 57% showed cross-reactivity by memory T cells.
‘We have now proven that, in some people, pre-existing T cell memory against common cold coronaviruses can cross-recognize SARS-CoV-2, down to the exact molecular structures,’ Weiskopf says. ‘This could help explain why some people show milder symptoms of disease while others get severely sick.’”