Epidemiological Features and Risk Factors of SARS-CoV-2 Reinfection: A Retrospective Cohort Analysis in Xiamen, China (Preprint)

BACKGROUND Recent surges in SARS-CoV-2 reinfections in China precipitated public concern, underscoring a gap in comprehensive population-based analyses of reinfection characteristics and risk factors. OBJECTIVE To investigate the epidemiological features and risk factors of SARS-CoV-2 reinfection in China. METHODS This study was conducted in Xiamen, China, analyzing reinfections classified into two cohorts: Delta-Omicron (cohort 1) and Omicron-Omicron (cohort 2). We employed descriptive epidemiology and an ensemble modeling approach. RESULTS A total of 327 cases were included with no fatalities reported during follow-up. The reinfection rate was 14.68% overall—22.51% for cohort 1 and 3.68% for cohort 2. Symptoms and hospitalizations were significantly lower during reinfections (47.92% symptomatic, 4.65% hospitalized) than during primary infections (99.69% symptomatic, 56.54% hospitalized). Persistent infections were more frequent during primary infection in cohort 1 (58.12%) compared to cohort 2 (0.74%). Most reinfections (83.33%) occurred post-relaxation of strict public health and social measures (PHSM). The time interval between primary infection and reinfection (Tpr) was notably longer for cohort 1 (median: 462.0 days) compared to cohort 2 (median: 280.0 days). The time from the most recent vaccination to the reinfection (Tvr) varied, with medians of 381.3 days (IQR: 167.9-594.7) and 395.0 days (IQR: 319.0-471.0) for cohorts 1 and 2, respectively. Reinfection risks increased over time were higher among less developed areas, those without persistent primary infection, primary infection with Delta variant, government and hospital workers, and the unvaccinated. CONCLUSIONS SARS-CoV-2 reinfection is less severe compared to the primary infection. The risk of SARS-CoV-2 reinfection increases over time associated with the gradual relaxation of stringent PHSM, pathogen evolution, and shift patterns in population immunity and contact.