Abstract: Objective To investigate the reinfection rate, clinical characteristics, and changes in antibody levels of SARS-CoV-2 among community residents in Baoshan District of Shanghai since January 2023, providing reference recommendations for the prevention and control strategy of SARS-CoV-2 reinfection. Methods Follow-up data from community sentinel residents in Baoshan District were utilized to collect information on infection or reinfection status every week. Clinical symptoms and disease outcomes were recorded. Additionally, 222 individuals were recruited from the follow-up cohort for quarterly assessments of neutralizing antibody levels. Chi-square test or Fisher's exact test were used to compare reinfection rates in different characteristic residents. The Mann-Whitney test was used to compare neutralizing antibody levels between two groups, and the Friedman test was used to compare relevant samples across multiple groups. Results A total of 230 new SARS-CoV-2 infections were reported among community sentinel residents in Baoshan District in 2023, with a cumulative number of infections reaching 938. Among these cases, there were 31 reinfections, indicating a reinfection rate of 3.30% (95% CI: 2.72%-3.89%). The number of new infections was highest in January (167 cases), all being primary infections. There was a small peak of infection from May to August, mainly consisting of reinfections. The number of infections gradually decreased from September to October. There was no significant difference in reinfection rates between different genders, ages, occupations, and whether they had underlying diseases (all P>0.05). The median interval between reinfection and primary infection was 209 (86) days. The main clinical manifestations of reinfection included fever (67.74%), cough (61.29%), and sore throat (48.39%), with antigens turning negative within a median time of 4(2) days. Residents vaccinated with ≥3 doses of the SARS-CoV-2 vaccine exhibited higher neutralizing antibody levels compared to those with fewer doses (P<0.05). Conclusions Reinfections of SARS-CoV-2 in Baoshan District of Shanghai tend to occur 6-7 months post-primary infection, predominantly presenting with mild symptoms. Comprehensive SARS-CoV-2 vaccination enhances long-term protective immunity via neutralizing antibodies.

Key words: SARS-CoV-2, Reinfection, Neutralizing antibody