NCP antigenemia and SARS-CoV-2-specific antibody responses
In sera of hospitalized COVID-19 patients without detectable antibodies,
NCP antigen was detected in high concentrations >100 pg/mL
(Fig. S1A,B). As expected, a subset of patients with detectable
antibodies against S1 or NCP had NCP antigen levels <2.97
pg/mL, consistent with successful clearance of the infection. We assumed
that the appearance of NCP-specific IgG would show a strong association
with the reduction of NCP antigenemia. Instead, we found that only
33.0% of anti-NCP-positive, but 40.6% of anti-S1-positive sera had an
NCP antigen concentration below the cutoff. Simultaneous detection of
antibodies and NCP antigen was also found (29.3% of S1 IgG-positive
sera, 38.3% of NCP IgG-positive sera, Fig. S1A,B). Accordingly, NCP
antigen was lower in anti-S1-positive compared to anti-NCP-positive sera
(Fig. S1C), suggesting that S1-specific IgG is more relevant than
NCP-specific IgG to reduce NCP antigenemia.