Epidemiological features and risk factors of SARS-CoV-2 reinfection: a retrospective cohort analysis in Xiamen, China

Recently, surges in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfections in China have raised public concern. We investigated the epidemiological features and risk factors for SARS-CoV-2 reinfection in China. A retrospective cohort study was conducted in Xiamen, China (2021-2023) with two subcohorts: Delta-Omicron (cohort 1) and Omicron-Omicron (cohort 2). Descriptive analysis and ensemble modeling were employed to evaluate reinfections. A total of 327 cases without fatalities were included. Reinfections accounted for 14.68% of cases, with 22.51% in cohort 1 and 3.68% in cohort 2. Compared with primary infections (PIs) (99.69% symptomatic, 56.54% hospitalized), reinfections were less severe, with fewer symptomatic instances (47.92%) and hospitalizations (4.65%). The majority of reinfections (83.33%) occurred following the relaxation of strict public health and social measures. The median time interval between PI and reinfection was longer for cohort 1 (462 days) than for cohort 2 (280 days). Reinfection risks were noted among lesser developed regions, those without persistent PI, those with primary Delta variant infection, government and hospital workers, and unvaccinated individuals. SARS-CoV-2 reinfections are generally less severe and are influenced by the relaxation of control measures, viral evolution, and changing patterns of population immunity and contact; this underscores the need for ongoing surveillance and targeted public health strategies to manage future infection waves.