A 14-year influenza reinfection surveillance in Chongqing, China: A retrospective analysis

Influenza poses a significant medical burden and has the potential to cause global pandemics. To better understand the epidemiological characteristics of influenza reinfections and identify factors associated with an increased risk of reinfection, we analyzed influenza data from 2010 to 2023 obtained from the National Notifiable Infectious Disease Reporting Information System in Chongqing, China. The Andersen-Gill model was used to evaluate the association between demographic characteristics and the risk of reinfection. A total of 676,811.47 person-years were observed, with a median time to reinfection of 9.40 months. The log-rank test revealed significant differences in reinfection probability by sex, age, occupation, and residence (<i>p</i> < .001). Independent risk factors for influenza reinfection included male sex (adjusted hazard ratio [a<i>HR</i>]: 1.026, 95% confidence interval [<i>CI</i>]: 1.004-1.049), age ≤ 5 years (aH<i>R</i>: 4.645, 95% <i>CI</i>: 4.292-5.027), 6-18 years (a<i>HR</i>: 3.891, 95% <i>CI</i>: 3.574-4.235), age 46-64 years (a<i>HR</i>: 1.336, 95% <i>CI</i>: 1.158-1.541), and age ≥ 65 years (a<i>HR</i>: 2.946, 95% <i>CI</i>: 2.533-3.426), urban residency (a<i>HR</i>: 1.353, 95% <i>CI</i>: 1.315-1.391), and preschool-aged children (a<i>HR</i>: 2.103, 95% <i>CI</i>: 1.830-2.416). Influenza reinfection in Chongqing is relatively common and significantly associated with several key factors, including male sex, age ≤ 18 or > 45 years, preschool-aged children, and urban residency. These findings underscore the importance of tailored public health strategies, particularly promoting influenza vaccination among at-risk groups, to protect vulnerable populations from reinfection. Future studies are needed to refine influenza prevention measures for at-risk individuals, especially those susceptible to reinfection.