Ten-year epidemiological and clinical insights of pediatric influenza A and B hospitalizations: an observational study

Infants and children under 5 years of age face a high risk of severe complications, including pneumonia and neurologic issues, from influenza virus infection. Hospital surveillance data can provide guidance for immunization recommendation policies to prevent severe influenza complications in the pediatric population. The aim of this study was to investigate the factors associated with influenza virus type and subtype in children and adolescents hospitalized with laboratory-confirmed influenza and compare the results obtained in previous analyses from 2010/11 to 2015/16 (P1) and 2016/17 to 2019/20 (P2). We carried out a retrospective descriptive study during ten influenza seasons (2010-2011 to 2019-2020) on laboratory-confirmed influenza in cases aged 0-17 years hospitalized for severe acute influenza virus infection (SHLCI). A total of 528 pediatric hospitalizations with laboratory-confirmed influenza were reported, 274 (51.9%) were male and 285 (54.0%) were aged 1-4 years. One hundred and two patients (19.3%) required ICU admission; 112 (21.2%) had preexisting comorbidities. The median length of stay was 5 days (range: 1-129). The main complications were pneumonia (61.8%), ARDS (29.7%) and 4 deaths. There was no significant difference in the incidence of complications according to virus type. The distribution according to influenza virus type and subtype was as follows: 79.4% had influenza A (43.7% H1N1pdm09, 14.1% H3N2), and 20.6% had influenza B. Only 5.4% had received the seasonal influenza vaccine. Our results confirm that, among the pediatric population, severe influenza predominantly affects younger children, who are often previously healthy, and is associated with substantial complications and ICU burden. The low degree of vaccination coverage among hospitalized children emphasizes the need to improve influenza immunization strategies in pediatric populations.