Enrollment nucleocapsid serostatus and antibody levels. Comparisons between nucleocapsid (N) seronegative (Ab−) and seropositive (Ab+) participants are shown for a) ID50 wild-type (Ab− N = 117, Ab+ N = 20), b) ID80 wild-type (Ab− N = 117, Ab+ N = 20), c) ID90 wild-type (Ab− N = 117, Ab+ N = 20), d) ID50 Delta (Ab− N = 117, Ab+ N = 20), e) ID80 Delta (Ab− N = 117, Ab+ N = 20), f) ID90 Delta (Ab− N = 117, Ab+ N = 20), g) wild-type ACE2 blocking (Ab− N = 103, Ab+ N = 18), h) wild-type spike-reactive IgG (Ab− N = 104, Ab+ N = 18), i) wild-type spike-reactive IgA (Ab− N = 104, Ab+ N = 18), j) Delta ACE2 blocking (Ab− N = 103, Ab+ N = 18), k) Delta spike-reactive IgG (Ab− N = 104, Ab+ N = 18), l) Delta spike-reactive IgA (Ab− N = 104, Ab+ N = 18), m) Delta spike-expressing cell opsonizing IgG MFI (Ab− N = 95, Ab+ N = 20), n) Delta spike-expressing cell opsonizing IgA MFI (Ab− N = 95, Ab+ N = 20), o) Delta ADCP (Ab− N = 111, Ab+ N = 20), p) Delta ADCD (Ab− N = 110, Ab+ N = 20), q) Delta ADCC (Ab− N = 95, Ab+ N = 20), r) Delta spike-expressing cell 50% IgG opsonization titer (Ab− N = 95, Ab+ N = 20), and s) Delta spike-expressing cell 50% IgA opsonization titer (Ab− N = 95, Ab+ N = 20). The red bar in all graphs is the median and statistical comparisons between N Ab− and N Ab+ participants were done using a Mann–Whitney test and the P values are indicated for each comparison.