A group from The University of Hong Kong, Hong Kong, SAR, China, etc. has reported on what differences in children and adults immunity drive COVID-19 pathogenesis.
https://www.nature.com/articles/s41467-021-24938-4
SARS-CoV-2 infection of children is associated with milder clinical outcomes than adults, and the immune mechanisms are unknown. Several hypotheses have been proposed to explain these differences such as innate cell recruitment and impairment by autoantibodies, mobilisation of antibody responses, differing levels of pre-existing cross-reactive immunity by common cold coronavirus exposure, or baseline total IgM levels.
Overall, it was found (1)total IFNγ CD4+ and CD8+ T cell responses are significantly lower in SARS-CoV-2 infected children than adults against the viral structural proteins, and in CD8+ T cells against ORF1ab proteins, and (2)prior β-coronavirus immunity is significantly lower in children than adults, indicating differing baseline immunity.
Therefore, reduced prior β-coronavirus immunity and reduced T cell activation in children might drive milder COVID-19 pathogenesis?
