Fig. 1.

SARS-CoV-2 neutralizing antibody (NtAb) titers in subjects with past SARS-CoV-2 infection measured at vaccination baseline (T0), 21 days after first-dose vaccination (T1) and 21 days after second-dose vaccination and NtAb titers measured at vaccination baseline (T0), 21 days after first-dose vaccination (T1) and 21 days after second-dose vaccination in subjects without past SARS-CoV-2 infection. The same symbols indicate the same subjects at different time points. Paired data were analyzed by Wilcoxon Signed Ranks Test. Asterisks indicate significance levels: ***p < 0.001; **p < 0.01; *p < 0.05