Influenza Vaccination and Protective Effectiveness Against Influenza Illness in Community‑Dwelling Children: A Prospective Cohort Study

Background Children are highly susceptible to influenza and face significant risks when infected, which makes vaccination a vital preventive measure. Still, there is limited real-world evidence, particularly from community-based studies, on whether the vaccine can reduce disease severity in children once they are diagnosed. Methods This prospective cohort study enrolled 388 children aged 6 months to 6 years diagnosed with influenza at the Longdong Community Health Service Center of Shenzhen Longgang Central Hospital between May 15, 2024, and October 16, 2025. Participants were categorized into vaccinated (n = 196) and unvaccinated (n = 192) groups based on vaccination history within the preceding year. Differences in clinical presentation, laboratory findings, healthcare resource utilization, and clinical outcomes were compared between the groups. Continuous variables were analyzed using the t-test or Mann-Whitney U test, and categorical variables were analyzed using the chi-square test. Results Compared to the unvaccinated group, vaccinated children had a lower body temperature (38.81 ± 0.58°C vs 39.03 ± 0.64°C), a shorter time to fever resolution (2.01 ± 1.21 days vs 2.45 ± 1.55 days), and lower incidences of myalgia (5.61% vs. 17.19%) and gastrointestinal symptoms (9.69% v. 20.83%) (all P  < 0.01). Regarding medical outcomes, the vaccinated group had fewer outpatient visits (1.55 ± 0.82 vs.1.78 ± 0.91), lower outpatient costs (349.42 ± 201.23 vs 407.41 ± 337.44; P  = 0.04), and lower rates of hospitalization (4.1% vs 21.9%) and antibiotic use (5.6% vs. 15.1%) ( P  < 0.01). Conclusion Among community-dwelling children, while influenza vaccination may not completely prevent infection, it can alleviate clinical symptoms of breakthrough infections, reduce the risk of hospitalization and antibiotic use, and decrease healthcare burden.