Abstract
BACKGROUND: Identifying those most susceptible to COVID-19 reinfection and understanding the associated characteristics is essential for developing effective prevention and control strategies. We aimed to evaluate the influence of social determinants, regional disparities, and variant evolution on COVID-19 reinfection rates. METHODS: We conducted a retrospective cohort study in São Paulo, Brazil, involving laboratory-confirmed COVID-19 patients. Reinfection was defined as a subsequent positive COVID-19 test at least 90 days after the previous confirmed infection. We assessed socioeconomic indicators, demographic factors, and spatial correlations. Reinfection rates were analyzed across different variants and subvariants. RESULTS: Among 73 741 patients, 5626 (7.6%) experienced reinfections, with most (95.0%) having 1 reinfection. Reinfection rates increased significantly during the Omicron period, particularly with subvariants BA.1, BA.2/BA.4, BA.5, and XBB/XBB.1.5/XBB.1.16. The highest rates were seen in patients initially infected during the BA.2/BA.4 and BA.5 periods, who were later reinfected by XBB subvariants. Socioeconomic indicators, including lower Human Development Index, higher proportions of informal settlements, and lower employment rates, were significantly associated with higher reinfection rates. Geospatial analysis showed significant clustering of reinfections in areas with higher social vulnerability. CONCLUSIONS: COVID-19 reinfection rates were heavily influenced by socioeconomic disparities and variant-specific factors. Regions with lower Human Development Index and worse socioeconomic conditions experienced higher reinfection rates. These findings highlight the need for targeted public health interventions focused on vulnerable populations, particularly in areas with greater social inequality. As new variants continue to emerge, ongoing surveillance and adaptive public health strategies will be critical to reducing reinfections.