Fig. 1.

Waning of anti-SARS-CoV-2 spike protein antibody titers from the last exposure to SARS-CoV-2 (infection or vaccination). Curves shown are the estimated trajectories adjusted for age (<40 or ≥40 years), sex (male or female), body mass index (<27.5 or ≥27.5 kg/m²), coexisting diseases (yes or no), immunosuppressant use (yes or no), smoking status (current or non-smoker), and frequency of alcohol drinking (<1 or ≥1 time/wk). A blue line shows participants who received 2-dose with infection-naïve (N = 2994), and a red line shows those who received 2-dose with a history of SARS-CoV-2 infection (N = 53). A green line shows those who received 3-dose with infection-naïve (N = 3582), and an orange line shows those who received 3-dose with a history of the infection (N = 272). Solid lines are the estimated geometric mean of anti-SARS-CoV-2 spike protein antibody titers, and shaded areas are the corresponding 95% CIs. N, number of measurements.