Human IgG and IgA responses to COVID-19 mRNA vaccines.

SARS-CoV-2 spike antigen-specific IgG and IgA elicited by infection mediate viral neutralization and are likely an important component of natural immunity, however, limited information exists on vaccine induced responses. We measured COVID-19 mRNA vaccine induced IgG and IgA in serum serially, up to 145 days post vaccination in 4 subjects. Spike antigen-specific IgG levels rose exponentially and plateaued 21 days after the initial vaccine dose. After the second vaccine dose IgG levels increased further, reaching a maximum approximately 7-10 days later, and remained elevated (average of 58% peak levels) during the additional >100 day follow up period. COVID-19 mRNA vaccination elicited spike antigen-specific IgA with similar kinetics of induction and time to peak levels, but more rapid decline in serum levels following both the 1st and 2nd vaccine doses (<18% peak levels within 100 days of the 2nd shot). The data demonstrate COVID-19 mRNA vaccines effectively induce spike antigen specific IgG and IgA and highlight marked differences in their persistence in serum.