Investigation of Nasal Mucosal IgA Responses in the Population Following COVID-19 Pandemic — China, September 2022–August 2023

What is already known about this topic?Mucosal IgA plays a crucial role in host immunity against respiratory viruses.Recent studies suggest that it has the potential to mitigate the transmission of the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)Omicron variant.However,a comprehensive population-based analysis examining mucosal IgA levels following the winter 2022 wave of the coronavirus disease 2019(COVID-19)pandemic is yet to be conducted.What is added by this report?In our study involving 3,421 participants,we documented IgA responses subsequent to SARS-CoV-2 infection.A significant proportion of individuals sustained increased levels of IgA for over six months.These levels were also observed in individuals with prior infections who underwent asymptomatic reinfections,indicating an active production of IgA antibodies.Further,individuals with multiple vaccinations or severe symptoms tended to display elevated IgA levels after recovery.What are the implications for public health practice?IgA in the nasal mucosa is crucial for defense against SARS-CoV-2 infection.These insights can enhance our knowledge of immune responses following infection and have provided certain reference values for disease prevention and control strategies.