TOPLINE Higher baseline nasal antigen-specific IgA was associated with markedly lower risk for influenza A H1N1 and SARS-CoV-2 over 4 months of home-based quantitative polymerase chain reaction (qPCR) surveillance. Intramuscular influenza and SARS-CoV-2 vaccination increased serum immunoglobulin (Ig)G but not nasal IgA and did not reduce risk for mild infection…
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