Immunogenicity during 6 months after SARS-CoV-2 infection is significantly different depending on previous COVID-19 vaccine regimens and a booster dose received.

Data on immunogenicity induced by SARS-CoV-2 infection and its sustainability are essential to inform COVID-19 vaccine schedule. A prospective cohort study was conducted among adults at-risk for COVID-19 during the Omicron variant-dominant epidemic. All were followed up for anti-spike RBD levels on days 0, 14, 90 and 180 after enrollment. Of the 871 individuals included, 264 (30.3 %) had COVID-19. Those with COVID-19 had significantly lower baseline geometric mean level of anti-spike RBD than those without COVID-19 (326 vs. 989; P < 0.001). Among the COVID-19 patients, anti-spike RBD level significantly increased the most at 14 days after infection and dropped significantly at day 90 and day 180. Giving a booster dose during 91-180 days after infection induced high level of anti-spike RBD through 180 days. These findings suggest high level but short-lived immunity induced by SARS-CoV-2 infection while sustained immunity required a booster dose administered from 90 days after the infection.