6-month SARS-CoV-2 antibody persistency in a Tyrolian COVID-19 cohort

Abstract

Background: As coronavirus disease 2019 caused by severe acute respiratory syndrome coronavirus 2 evolved only recently, the persistency of the anti-viral antibody response remains to be determined.

Methods: We prospectively followed 29 coronavirus disease 2019 cases, mean age 44 ± 13.2 years. Except for one participant with a pre-existing diagnosis of rheumatoid arthritis, all other participants were previously healthy. We determined anti-viral binding antibodies at 2-10 weeks, 3 months, and 6 months after disease onset as well as neutralizing antibodies at 6 months. Two binding antibody assays were used, targeting the S1 subunit of the spike protein, and the receptor binding domain.

Results: All participants fully recovered spontaneously except for one who had persisting hyposmia. Antibodies to the receptor binding domain persisted for 6 months in all cases with a slight increase of titers, whereas antibodies to S1 dropped below the cut-off point in 2 participants and showed a minimal decrease on average, mainly at month 3 of follow-up in males; however, neutralizing antibodies were detected in all samples at 6 months of follow-up.

Conclusion: There is a stable and persisting antibody response against acute respiratory syndrome coronavirus 2 at 6 months after infection. Neutralizing antibodies confirm virus specificity. As the number of coronavirus disease 2019 convalescent cases is increasing sharply, antibody testing should be implemented to identify immunized individuals. This information can be helpful in various settings of professional and private life.

Keywords: ELISA; Immunity; Neutralizing; Prospective; Virus.

Fig. 1

Anti-SARS-CoV‑2 antibody index values over time. a Antibody index values for the S1 IgG assay at 3 consecutive time points. Lines indicate median values and error bars show interquartile ranges. Corrected p-values are shown above the brackets. Spearman correlation coefficients for T1 vs. T2 was 0.89, and for T1 vs. T3 it was 0.70 (p-value <0.001 for both). Of note, at T1 (months 1–2) data of 4 individuals are missing. In each column one patient occurs only once. b Antibody index values for the RBD pan-Ig assay at three consecutive time points. Lines indicate median values and error bars show interquartile ranges. Corrected p-values are shown above the brackets. Spearman correlation coefficients for T1 vs. T2 was 0.65, and for T1 vs. T3 it was 0.49 (p-value <0.02 for both). Of note, at T1 (months 1–2) data of 4 individuals are missing. In each column one patient occurs only once. c S1 IgG indices by sex. Levels remained stable in females with median (95% CI) values at T1, T2 and T3 of 3.5 (2.3–8.2), 3.8 (1.6–7.5) and 3.95 (1.0–7.0), respectively, whereas a decline was observed in males with values at T1, T2 and T3 of 6.7 (3.6–10.6), 4.3 (2.1–7.9), and 4.1 (1.5–6.6), respectively. None of the differences were significant

Fig. 2

Individual time course of S1 IgG and RBD pan-Ig antibody indices. a Individual longitudinal S1 IgG index values. The dashed horizontal line indicates the cut-off point between negative and positive results. b Individual longitudinal RBD pan-Ig index values. The dashed horizontal line indicates the cut-off point between negative and positive results