Infants More Susceptible Than Older Children to Severe Illness from Viruses

In a new study published in the journal Pediatrics, researchers found infants are far more vulnerable than older children to severe illness from viruses such as influenza, respiratory syncytial virus (RSV), human metapneumovirus (hMPV) and SARS-CoV-2.

In the study, researchers collected weekly mid-turbinate nasal swabs and biweekly symptom surveys from November 2019 to August 2025 from a longitudinal birth cohort of healthy U.S. infants and children in Cincinnati, Ohio. Nasal swabs were tested for pathogen targets on the Luminex NxTAG Respiratory Pathogen Panel and the Flu SC2 assay. They then linked pathogen-specific infections to the temporally-corresponding symptom surveys. Co-infections were removed to observe only independent pathogen symptomologies.

Out of 15,898 acute respiratory illnesses from 1,223 unique children, the researchers found that compared with older children, infants were more likely to experience respiratory distress/dyspnea with influenza A (odds ratio [OR] = 4.73), RSV A (OR = 2.52), RSV B (OR = 2.22), hMPV (OR = 2.36) and SARS-CoV-2 (OR = 3.99), but not influenza B or parainfluenza. In addition, hospital and emergency department medical attention was similarly associated. Influenza A had greater odds of fever (OR = 2.77) and anorexia (OR = 2.94) compared with influenza B. Asymptomatic infections were frequent. More than three-quarters of symptomatic episodes were treated at home. And, vomiting and/or diarrhea occurred during one-quarter of RSV and one-third of influenza infection episodes.

According to the researchers, “Our results highlight extraordinary variability in respiratory tract infection symptoms and outcomes in a U.S. cohort of healthy children. Understanding why some young children suffer severe symptoms and others remain relatively unscathed could unlock actionable opportunities to improve child health.”