Streptococcus pyogenespharyngitis elicits diverse antibody responses to key vaccine antigens influenced by the imprint of past infections.

Knowledge gaps regarding human immunity toStreptococcus pyogeneshave impeded vaccine development. To address these gaps and evaluate vaccine candidates, we established a human challenge model ofS. pyogenespharyngitis. Here, we analysed antibody responses in serum and saliva against 19 antigens to identify characteristics distinguishing 19 participants who developed pharyngitis and 6 who did not. Pharyngitis elicited serum IgG responses to key vaccine antigens and a muted mucosal IgA response, whereas the 6 participants without pharyngitis had more pronounced IgA responses and minimal IgG responses. Serum IgG responses to pharyngitis in adult participants resembled those observed in children and were inversely correlated with the magnitude of pre-existing responses. While a straightforward correlate of protection was not evident, baseline antibody signatures distinguished clinical and immunological outcomes following experimental challenge. This highlights the influence of a complex humoral imprint from previous exposure, relevant for interpreting immunogenicity in forthcoming vaccine trials.