Assay dependence of long-term kinetics of SARS-CoV-2 antibodies

Abstract

Since the worldwide outbreak of the novel coronavirus (SARS-CoV-2), the question raised whether infected patients would elicit long-lasting protective immunity. Several companies developed serological assays for the detection of SARS-CoV-2 antibodies. In this study, we compared 4 different serology assays in convalescents up to 7 months post-infection. Both Abbott assays showed a significative decrease of IgG antibodies over time. Whereas the Elecsys Anti‑SARS‑CoV‑2 N assay (Roche) initially showed a significant increase, antibody titers significantly decreased at the latest timepoint. Although not significant, the Elecsys Anti‑SARS‑CoV‑2 S assay (Roche) showed tendency towards increasing titers overtime. Our data showed that results of SARS-CoV-2 serology should be interpreted with caution.

Keywords: Covid-19; Immunoassay; Long-term kinetics; SARS-CoV-2.

Fig. 1

Results of antibody responses against SARS-CoV-2. First timepoint (0: median 34 days after positive PCR or symptoms) is used as starting point (=100%). Other timepoints are normalized to this first point (T1: median 78 days; T2: median 179 days; T3: median 223 days). Assay 1 is the SARS-CoV-2 IgG assay (Abbott). Assay 2 is the SARS-CoV-2 IgG II Quant assay (Abbott). Assay 3 and 4 are respectively the Elecsys Anti‑SARS‑CoV‑2 (Roche) and Elecsys Anti‑SARS‑CoV‑2 S (Roche) assay. Statistics were performed by means of Wilks’ lambda MANOVA test. Significant difference is shown by “s” symbol on the graph, whereas non-significance is shown by “ns”-symbol. Boxplots show a horizontal line as mean value, together with upper 75 and lower 25 percentiles.

Fig. 2

Individual results of antibody responses against SARS-CoV-2. Timepoints: T0: median 34 days after positive PCR / first symptoms; T1: median 78 days; T2: median 179 days; T3: median 223 days. The dotted line represents the cut off proposed by the manufacturer.