Differences in humoral responses between children and adults
Multiplex systems analysis of antibody responses in saliva found distinct SARS-CoV-2 specific antibody responses in infected children compared to adults during the acute phase of infection (Figure 3A). Three SARS-CoV-2 antibody features (IgA1 to Spike 1, IgA1 to nucleocapsid protein (NP), IgA2 to NP, Figure 3B) were identified by dimensionality reducing analysis (least absolute shrinkage and selection operator (LASSO)) as significantly elevated responses in adult saliva compared to children (Supplementary Figure 3, p =0.0023, p <0.001, p <0.001 respectively), thus suggesting that adults and children generate distinct mucosal antibody responses during the acute phase of infection.
Given we observed different antibody profiles in the saliva between adults and children, multiplex systems analysis was also conducted on acute children and adult plasma samples. This analysis identified three elevated antibody features that were unique to adult plasma (C1q Trimer S C1q (Marker of antibody-mediated complement activation) to Trimer S, IgG4 to RBD, IgA2 to NP, Supplementary Figure 4).
Secondary attack rate when including comprehensive virological and antibody assessment Evidence of SARS-CoV-2 exposure was observed in saliva and plasma antibody responses in 62% of household contacts who tested negative by NPS (26/42: 7/42 serology, 24/42 saliva antibodies, Supplementary Figure 1). Therefore, the secondary attack rate when respiratory (NPS) and non-respiratory measures were included (saliva PCR, stool PCR, plasma antibodies, saliva antibodies) was 76% (50/66). There was no onward transmission from participants who tested negative by NPS, even if they were PCR positive in other biological samples.