A retrospective cohort study on COVID-19 reinfections and associated factors during six waves of the pandemic in Mexico

Background. Monitoring reinfections helps predict peaks, variant emergence, and immunity trends. While reinfection rates between 3 and 31 % have been reported, a better understanding of their variation in different geographical areas could guide prevention and vaccination efforts. Aims. This study examines the incidence of COVID-19 reinfection and associated factors in Mexico over six pandemic waves. Rapid mutation of SARS-CoV-2 generates variants that affect reinfection rates and population immunity. Methods. In this retrospective cohort study, data from 3,236,259 primary infections were analyzed, and 212,892 reinfections were identified. Results. Sex, age, vaccination status, and initial infection severity were found to be significant predictors of reinfection. Furthermore, the risk of reinfection decreased with wave progression, especially for those infected during the first wave. Reduced risk of reinfection after hospitalization suggests improved exposure prevention. Results indicated increased reinfection rates during the Omicron wave, particularly for those who were originally infected during the first wave, with women and middle-aged groups at higher risk. Conclusions. Our results highlight the intricate relationship between viral evolution, immunity, and demographics, which is crucial for effective pandemic management and vaccination strategies. (c) 2024 Published by Elsevier Inc. on behalf of Instituto Mexicano del Seguro Social (IMSS).