Comparative performance of the InBios SCoV-2 Detect (TM) IgG ELISA and the in-house KWTRP ELISA in detecting SARS-CoV-2 spike IgG antibodies in Kenyan populations.

BACKGROUND: The InBios SCoV-2 Detect™ IgG ELISA (InBios) and the in-house KWTRP ELISA (KWTRP) have both been used in the estimation of SARS-CoV-2 seroprevalence in Kenya. Whereas the latter has been validated extensively using local samples, the former has not. Such validation is important for informing the comparability of data across the sites and populations where seroprevalence has been reported. METHODS: We compared the assays directly using pre-pandemic serum/plasma collected in 2018 from 454 blood donors and 173 malaria cross-sectional survey participants, designated gold standard negatives. As gold standard SARS-CoV-2 positive samples: we assayed serum/plasma from 159 SARS-CoV-2 PCR-positive patients and 166 vaccination-confirmed participants. RESULTS: The overall agreement on correctly classified samples was >0.87 for both assays. The overall specificity was 0.89 (95% CI, 0.87-0.91) for InBios and 0.99 (95% CI, 0.97-0.99) for KWTRP among the gold standard negative samples while the overall sensitivity was 0.97 (95% CI, 0.94-0.98) and 0.93 (95% CI, 0.90- 0.95) for InBios and KWTRP ELISAs respectively, among the gold standard positive samples. In all, the positive predictive value for InBios was 0.83 (95% CI, 0.79-0.87) and 0.98 (95% CI, 0.96-0.99) for KWTRP while the negative predictive value was 0.98 (95% CI, 0.97- 0.99) and 0.97 (95% CI, 0.95-0.98) for InBios and KWTRP respectively. CONCLUSIONS: Overall, both assays showed sufficient sensitivity and specificity to estimate SARS-CoV-2 antibodies in different populations in Kenya.