Which test results to believe? Comparison of different ELISA kits for detection of SARS-CoV-2-neutralizing antibody among COVID-vaccinated individuals.

BACKGROUND

In the context of SARS-CoV-2, infection and immunization lead to varied levels of neutralizing antibodies (NAbs) crucial for protective immunity. In the lack of universal availability of plaque reduction neutralization tests, the gold standard centers rely on surrogate kits, for which performance standards and validation are lacking. Hence, we assessed three NAb kits available in India to determine their agreement and concordance.

METHODS

It's a single-center cross-sectional observation study conducted during the third wave of the pandemic starting in January 2022 amongst individuals (n: 247) who received the first two doses of Covishield. Samples were analysed using kit-A (Indian Council of Medical Research (ICMR) approved NAb microlisa kit, J. Mitra & Co. Pvt. Ltd), kit-B (Food and Drug Administration-approved NAb surrogate virus neutralisation test, GenscriptTM), and kit-C (NARI- and ICMR-approved anti-SARS-CoV-2 IgG antibodies kit using indirect ELISA principle, ErbaLisa® COVID-19 IgG). Cohen's kappa and concordance were analyzed using JMPver20.0.0.

RESULTS

NAb was detected in 80.4%, 82.9%, and 21% samples using the three different kits. Discordance was observed in 19.68%, 65.7%, and 62.6% between Kit A-B, A-C, and B-C, respectively. The agreement was fair between Kit A-B (κ-0.35; p: 0.06) and Kit B-C (κ-0.09; p: 0.0005). Kit-B showed higher mean percentage inhibition (74.6 ± 32.1%) than Kit-A (68.1 ± 35.7%) (p: 0.0347). The correlation between kit-A and kit-B was moderate (r: 0.57; p < 0.0001).

CONCLUSION

There is significant discordance between various commercials, which raises questions about their validity. The research underscores the need for robust validation and standardization of NAb tests to ensure their reliability and effectiveness in guiding public health strategies.