Pediatric influenza and illness severity: what is known and what questions remain?

Purpose of review Influenza causes a range of illnesses in children, from uncomplicated self-limited illness to severe disease and death. This review provides an update on the severity and burden of influenza in US children over recent seasons. Recent findings The 2017-2018 influenza season was widespread and severe across all ages, including children. Disease severity is influenced by influenza virologic characteristics and host factors, as well as public health interventions such as influenza vaccination and antiviral treatment. In recent influenza A(H3N2)-predominant seasons (2016-2017 and 2017-2018), influenza vaccination effectiveness was higher in younger children compared with older children and adolescents, although the reasons for this are unclear. Interestingly, even in seasons when influenza A(H3N2) viruses predominate, influenza A(H1N1) pdm09 and B viruses can play a large role in severe pediatric disease. Although children less than 5 years of age and those with underlying medical conditions are at increased risk for severe disease, influenza-associated hospitalizations and deaths occur every season in healthy children. Summary Influenza causes a substantial burden of outpatient visits, hospitalizations, and deaths among children. Ongoing research is important to better characterize factors that contribute to influenza severity, and to identify strategies to improve the impact of influenza vaccination and treatment.