RESUMEN
BACKGROUNDCharacterizing the humoral immune response to SARS-CoV-2 and developing accurate serologic assays are needed for diagnostic purposes and estimating population-level seroprevalence. METHODSWe measured the kinetics of early antibody responses to the receptor-binding domain (RBD) of the spike (S) protein of SARS-CoV-2 in a cohort of 259 symptomatic North American patients infected with SARS-CoV-2 (up to 75 days after symptom onset) compared to antibody levels in 1548 individuals whose blood samples were obtained prior to the pandemic. RESULTSBetween 14-28 days from onset of symptoms, IgG, IgA, or IgM antibody responses to RBD were all accurate in identifying recently infected individuals, with 100% specificity and a sensitivity of 97%, 91%, and 81% respectively. Although the estimated median time to becoming seropositive was similar across isotypes, IgA and IgM antibodies against RBD were short-lived with most individuals estimated to become seronegative again by 51 and 47 days after symptom onset, respectively. IgG antibodies against RBD lasted longer and persisted through 75 days post-symptoms. IgG antibodies to SARS-CoV-2 RBD were highly correlated with neutralizing antibodies targeting the S protein. No cross-reactivity of the SARS-CoV-2 RBD-targeted antibodies was observed with several known circulating coronaviruses, HKU1, OC 229 E, OC43, and NL63. CONCLUSIONSAmong symptomatic SARS-CoV-2 cases, RBD-targeted antibodies can be indicative of previous and recent infection. IgG antibodies are correlated with neutralizing antibodies and are possibly a correlate of protective immunity.
RESUMEN
ObjectivesNumerous serologic immunoassays have been launched to detect antibodies to SARS-CoV-2, including rapid tests. Here, we validate use of a lateral flow immunoassay (LFI) intended for rapid screening and qualitative detection of anti-SARS-CoV-2 IgM and IgG in serum, plasma, and whole blood, and compare results with ELISA. We also seek to establish the value of LFI testing on blood obtained from a capillary blood sample. MethodsSamples collected by venous blood draw and capillary finger stick were obtained from patients with SARS-CoV-2 detected by RT-qPCR and control patients negative for SARS-CoV-2. Samples were tested with the 2019-nCoV IgG/IgM Detection Kit (Colloidal Gold) lateral flow immunoassay, and antibody calls were compared with results obtained by ELISA. ResultsThe Biolidics LFI kit shows clinical sensitivity of 92% at 7 days after PCR diagnosis of SARS-CoV-2 on venous blood. Test specificity was 92% for IgM and 100% for IgG. There was no significant difference in detecting IgM and IgG with Biolidics LFI and ELISA at D0 and D7 (p=1.00), except for detection of IgM at D7 (p=0.04). Finger stick whole blood of SARS-CoV-2 patients showed 93% sensitivity for antibody detection. ConclusionsClinical performance of Biolidics 2019-nCoV IgG/IgM Detection Kit (Colloidal Gold) is comparable to ELISA and showed consistent results across different sample types. Furthermore, we show that capillary blood obtained by finger stick shows similar sensitivity for detecting anti-SARS-CoV-2 IgM and IgG antibodies as venous blood samples. This provides an opportunity for decentralized rapid testing in the community and may allow point-of-care and longitudinal self-testing for the presence of anti-SARS-CoV-2 antibodies.