Background: Sero-surveillance of SARS-CoV-2 is crucial to monitoring levels of population exposure and informing public health responses, but may be influenced by variability in performance between available assays .
Methods: Five commercial immunoassays and a neutralising activity assay were used to detect antibodies to SARS-CoV-2 in routine primary care and paediatric samples collected during the first wave of the pandemic in NHS Lothian, Scotland as part of ongoing surveillance efforts . For each assay, sensitivity and specificity was calculated relative to consensus results and neutralising activity . Quantitative correlation was performed between serological and neutralising titres .
Results: Seroprevalence ranged from 3.4-7.3% in primary care patients and 3-5.9% in paediatric patients according to different immunoassays . Neutralising activity was detectable in 2.8% and 1.3% respectively . Relative assay performance changed depending on comparison to immunoassay consensus versus neutralising activity and qualititative versus quantitative agreement . Cross-reactivity with endemic seasonal coronaviruses was confirmed by neutralising assay in false positives for one immunoassay . Presence of false positives for another assay was found specifically in paediatric but not adult samples .
Conclusions: Five serological assays show variable accuracy when applied to the general population, impacting seroprevalence estimates . Assay performance may also vary in detection of protective neutralising antibody levels . These aspects should be considered in assay selection and interpretation in epidemiological studies.