Clinical features and outcomes of influenza by virus type/subtype/ lineage in pediatric patients

Background: Recently, four influenza viruses are circulating worldwide: A(H1N1)pdm09, A(H3N2), B/ Victoria, and B/Yamagata. However, information on the clinical differences among pediatric patients infected with four recently circulating influenza viruses is sparse. Methods: Medical records of pediatric patients (<20 years of age) diagnosed with influenza between the 2014–2015 and 2018–2019 influenza seasons were retrospectively reviewed. Clinical features were compared between (I) patients infected with influenza A (FluA) and influenza B (FluB) viruses, (II) patients infected with FluA when A(H1N1)pdm09 and A(H3N2) circulated dominantly, and (III) patients infected with FluB when B/Victoria and B/Yamagata circulated dominantly. Results: A total of 1,588 patients infected with FluA and 964 patients infected with FluB were included in this study. Patients infected with FluB were older (P<0.001) and more likely to report sore throat (P=0.002) than those infected with FluA. Otherwise, there were no significant differences in the clinical symptoms, diagnoses, and outcomes between patients infected with FluA and FluB. Overall, clinical features of influenza patients were similar regardless of the dominantly circulated subtype and lineage of the virus. In children aged ≤2 years, patients infected with FluB were more like to experience lower respiratory tract infection (P=0.034) and hospitalization (P=0.001) than those infected with FluA. Conclusions: There were no significant clinical differences among pediatric patients infected with four recently circulating influenza viruses, except that FluB infection tended to be more severe than FluA infection in children aged ≤2 years.