<b>How blood group A evolution is associated with reduced innate immunity and doubles the host's exposure to pathogens, as suggested by SARS-CoV-2 (COVID-19) infection. </b>— <b><i>Brief communication</i></b><b><i> </i></b><i>—</i>

<br>The formation of evolutionary hybrid Tn (T “nouvelle”) cross-reactive A antigens, together with A-allelic mucin-type glycosylations on cell surfaces and plasma proteins, doubles the host's exposure to pathogens by two genetically distinct bindings, neutralising the innate anti-Tn/A reactivities of pre-existing polyreactive IgM. The consequent protection against A-phenotypic autoimmunity implies a reduction in innate immunity, which explains the increased susceptibility and severity of disease in blood group A individuals, as suggested by SARS-CoV-2 (COVID-19) infection.<br><br>