Initial characterisation of ELISA assays and the immune response of the clinically correlated SARS-CoV-2 biobank SERO-BL-COVID-19 collected during the pandemic onset in Switzerland

Kaltenbach, H.-M.; Rudolf, F.; Linnik, J.; Deichmann, J.; Ruf, T.; Altamura, R.; Kapetanovic, E.; Mason, D.; Wagner, B.; Goetz, T.; Mundorff, L.; Stoll-Rudin, K.; Krebs, C.; Renz, T.; Hochueli, T.; Haymoz, S.; Hosch, M.; Periat, N.; Richert, M.; Sesia, S.; Paris, D.; Quinto, C. B.; Probst-Hensch, N.; Niederhauser, C.; Reddy, S.; Nickel, B.; Savic, M.

Background: To accurately measure seroprevalance in the population, boththe expected immune response as well as the assay performances have to be well characterised. Here, we describe the collection and initial characterisation of a blood and saliva biobank obtained after the initial peak of the SARS-CoV-2 pandemic in Switzerland. Methods: Two laboratory ELISA assays measuring IgA & IgG (Euroimmun), and IgM & IgG (Epitope Diagnostics) were used to characterise the biobank collected from 349 re- and convalescent patients from the canton of Basel-Landschaft. Findings: The antibody response in terms of recognized epitopes is diverse, especially in oligosymptomatic patients, while the average strength of the antibody response of the population does correlate with the severity of the disease at each time point. Interpretation: The diverse immune response presents a challenge when conducting epidemiological studies as the used assays only detect 90% of the oligosymptomatic cases. This problem cannot be rectified by using more sensitive assays or lower cut-offs as they concomitantly reduce specificity. Funding Funding was obtained from the Amt fur Gesundheit of the canton Basel-Landschaft, Switzerland.