Test performance evaluation of SARS-CoV-2 serological assays

Appropriate use and interpretation of serological tests for assessments of SARS-CoV-2 exposure, infection and potential immunity require accurate assay performance data. We conducted a head-to-head evaluation of 10 point-of-care (POC) style lateral flow assays (LFAs) and two laboratory-based enzyme-linked immunosorbent assays (ELISAs) to detect anti-SARS-CoV-2 IgM and IgG antibodies by 5-day time intervals from symptom onset and the specificity of each assay in pre-COVID-2019 specimens. The percent of seropositive individuals increased with time, peaking in the latest time interval tested (>20 days after symptom onset). Test specificity was heterogeneous (ranging from 84.3–100.0%) and was predominantly affected by variability in IgM results. LFA specificity could be increased by considering weak bands as negative, but this decreased detection of antibodies in a subset of SARS-CoV-2 real-time polymerase chain reaction (RT-PCR)-positive cases. Our results indicate the importance of seropositivity threshold determination and reader training for reliable LFA deployment. Informed use of serology will require evaluations covering the full spectrum of SARS-CoV-2 infections, from asymptomatic and mild infection to severe disease, and later convalescence. Well-designed studies to elucidate the mechanisms and serological correlates of protective immunity will be crucial to guide rational clinical and public health policies.