Understanding mucosal antibody responses from SARS-CoV-2 infection and/or vaccination is crucial to develop strategies for longer term immunity, especially against emerging viral variants. We profiled serial paired mucosal and plasma antibodies from COVID-19 vaccinated only vaccinees (vaccinated, uninfected), COVID-19–recovered vaccinees (recovered, vaccinated), and individuals with breakthrough Delta or Omicron BA.2 infections (vaccinated, infected). Saliva from COVID-19–recovered vaccinees displayed improved antibody-neutralizing activity, Fcγ receptor (FcγR) engagement, and IgA levels compared with COVID-19–uninfected vaccinees. Furthermore, repeated mRNA vaccination boosted SARS-CoV-2–specific IgG2 and IgG4 responses in both mucosa biofluids (saliva and tears) and plasma; however, these rises only negatively correlated with FcγR engagement in plasma. IgG and FcγR engagement, but not IgA, responses to breakthrough COVID-19 variants were dampened and narrowed by increased preexisting vaccine-induced immunity against the ancestral strain. Salivary antibodies delayed initiation following breakthrough COVID-19 infection, especially Omicron BA.2, but rose rapidly thereafter. Importantly, salivary antibody FcγR engagements were enhanced following breakthrough infections. Our data highlight how preexisting immunity shapes mucosal SARS-CoV-2–specific antibody responses and has implications for long-term protection from COVID-19.


Kevin J. Selva, Pradhipa Ramanathan, Ebene R. Haycroft, Arnold Reynaldi, Deborah Cromer, Chee Wah Tan, Lin-Fa Wang, Bruce D. Wines, P. Mark Hogarth, Laura E. Downie, Samantha K. Davis, Ruth A. Purcell, Helen E. Kent, Jennifer A. Juno, Adam K. Wheatley, Miles P. Davenport, Stephen J. Kent, Amy W. Chung


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