Fig 1.
Detection of SARS-CoV-2 specific antibodies.
Plasma samples collected from study volunteers were tested by ELISA against SARS-CoV-2 RBD, full length S protein and N protein. Panel A shows results with plasma from three representative subjects with confirmed COVID-19 infection along with negative, high positive and low positive control samples. Panel B shows results from eight study subjects without a PCR-based confirmatory test. The horizontal line represents the cutoff value for positivity based on reactivity with S or RBD for plasma samples collected from healthy control volunteers prior to October, 2019. The cutoff value was set at two standard deviations above the mean optical density of the plasma samples collected from healthy control volunteers prior to October, 2019. Optical density readings were normalized against the level of the high positive standard run on each ELISA.
Fig 2.
Assessment of selective antibody binding to SARS-CoV-2 nucleocapsid (N) protein.
Twelve subjects with antibody levels against SARS-CoV-2 spike RBD and S that were below the cut off value for positivity had detectable antibodies against SARS-CoV-2 N protein (A). To test whether this was due to cross-reactivity against common β-coronavirus N proteins, we compared antibody binding to SARS-CoV-2, OC43 and HKU1 N proteins (B). Optical density readings were normalized against the level of the high positive standard run on each ELISA.
Table 1.
Categorization of subjects recruited into COVID-19 serology study in NL.
Fig 3.
Distribution of study subjects with confirmed or suspected COVID-19.
Of 263 individuals recruited, 46 had previous SARS-CoV-2 infection confirmed by PCR testing. All were subsequently tested by ELISA for antibodies against SARS-CoV-2 S and N proteins with results summarized as shown.
Table 2.
Age, sex and symptoms of persons suspecting exposure to SARS-CoV-2 without PCR-based diagnosis of active infection or serological evidence of past infection.