Objective: To analyze the long-term epidemiological trends of acute intestinal infections (AII) among children under 5 years old and to evaluate the population-level effectiveness of the national rotavirus vaccination (RVV) program as a primary preventive intervention. Methods: A retrospective, population-based cohort study was conducted using data from the [Country's] National Infectious Disease Surveillance Registry from January 2015 to December 2024. We included all reported cases of AII in children <5 years old. The study period was divided into pre-vaccine (2015-2018) and post-vaccine (2020-2024) periods, excluding the 2019 implementation year. Primary outcomes were the incidence of all-cause AII hospitalizations and laboratory-confirmed rotavirus hospitalizations per 100,000 child-years. Incidence Rate Ratios (IRR) were calculated using Poisson regression to compare the pre- and post-vaccine periods. Results: A total of 185,210 all-cause AII hospitalizations in children <5 were recorded during the study period. In the post-vaccine period, the incidence of laboratory-confirmed rotavirus hospitalizations decreased by 85.2% (from 812.5 to 119.9 per 100,000; IRR: 0.148; 95% CI: 0.13-0.17; p<0.001). The incidence of all-cause AII hospitalizations also declined significantly, dropping by 35.7% (from 2,150.4 to 1,382.7 per 100,000; IRR: 0.643; 95% CI: 0.61-0.68; p<0.001). A shift in etiology was observed, with Norovirus becoming the leading identified pathogen in hospitalized cases post-vaccination (40.5%). The distinct winter seasonality of AII was significantly blunted in the post-vaccine period. Conclusion: The national rotavirus vaccination program has been highly effective, leading to a profound reduction in the burden of severe rotavirus disease and a significant (35.7%) decrease in all-cause AII hospitalizations. The epidemiological landscape has shifted, with Norovirus emerging as the primary etiological challenge. These findings underscore the success of vaccination and highlight the continued importance of parallel preventive measures, such as hygiene (WASH) and the potential need for future polyvalent vaccines.

Epidemiology, acute intestinal infections, pediatrics, preventive measures, effectiveness, rotavirus vaccine, vaccination, surveillance, incidence, public health.

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