Remembering seasonal coronaviruses

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has differential effects according to age, with symptomatic and severe infections mostly occurring in older adults. One possible explanation for this variation is that children and younger adults have more preexisting immunity against seasonal human coronaviruses (HCoVs) that cross-react with SARS-CoV-2, providing protection from severe and even symptomatic SARS-CoV-2 infection. Consistently, SARS-CoV-2 cross-reactive memory CD4+ and CD8+ T cells against the spike protein, the major surface protein of coronaviruses, have been reported in unexposed individuals.

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