CIDRPA reports: Infants are far more vulnerable than older children to severe illness from viruses like influenza, respiratory syncytial virus (RSV), human metapneumovirus (hMPV), and SARS-CoV-2, the virus that causes COVID-19, according to a study yesterday in Pediatrics. 

The findings also highlight significant differences in how respiratory infections affect infants, ranging from asymptomatic or mildly symptomatic infections managed at home to severe illness requiring hospital or emergency department (ED) care. 

For the study, researchers led by a team from Cincinnati Children's Hospital Medical Center followed up with 1,223 healthy children from birth to age 5 years from November 2019 to August 2025. After collecting weekly nasal swabs from participants and pairing the laboratory results with biweekly symptom surveys, the team identified 15,898 acute respiratory infections (ARIs) caused by different pathogens.

Both silent and severe infections

Overall, more than three-quarters (78.4%) of symptomatic respiratory infections were managed at home, and the remaining 21.6% were treated in a healthcare setting. 

The researchers identified asymptomatic infections for all respiratory pathogens, including influenza (7.6%) and RSV (10.2%). Infants younger than 1 year experienced the most asymptomatic flu and RSV infections—14.5% and 12.5%, respectively. 

No symptoms were reported in one-fifth of SARS-CoV-2, adenovirus, and endemic coronavirus infections or in one-third of rhinovirus and bocavirus infections.

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CIDRAP - Center for Infectious Disease Research & Policy
Research and Innovation Office, University of Minnesota, Minneapolis, MN

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