Fig. 3

Anti-N antibody titres and dynamics in subjects previously infected by SARS-CoV-2. a-b) Observed antibody titres in subjects infected by SARS-CoV-2 and tested in May 2020, November 2020 and June 2021 with Abbott (n=65, P < 0.0001 from November 2020 to June 2021) and Roche assays (n=65, P < 0.0001 from November 2020 to June 2021). The horizontal line represents the median, the vertical line represents the 95% confidence intervals. c, d Observed individual-level paired antibody titres in subjects infected by SARS-CoV-2 and tested in May 2020, November 2020 and June 2021. In June 2021, 13.8% (9 out of 65 subjects, 95% CI 6.5–24.7%) and 95.4% (62 out of 65 subjects, 95% CI 87.1–99.0) resulted positive to Abbott and Roche assays respectively, more than 15 months post infection. Subjects with increasing titres are coloured in green, and subjects with a negative result in June 2021 are presented in red. e, f Estimated antibody decay rate distribution calculated among subjects infected by SARS-CoV-2 in February/March 2020 and tested in May 2020, November 2020, and June 2021. Each bar represents the frequency of each slope (in units of days), calculated on the logarithm of individual-level sequential titres. We estimated a median half-life of 115 (95% CI 105–126) days and 179 (95% CI 153–255) days for the antibodies detected by the Abbott and Roche assays, respectively. To estimate the median half-life, only subjects with no doubling antibodies from May 2020 were considered. Asterisks indicate *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Statistical significance of antibody levels was evaluated by Friedman test followed by Dunn’s multiple comparisons test