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Normally at this time of year, Intermountain Primary Children’s Hospital is filled with ill infants and toddlers who are being treated for respiratory complications due to RSV and flu. Some of these young patients require ICU care and assistance from mechanical ventilators to breathe.

This year, Primary Children’s Hospital has had no pediatric RSV or flu patients admitted to the hospital, which is unheard of. Influenza infections, which can be severe in young children, are also extremely rare this year.

The safety measures that people are taking during the COVID-19 pandemic can explain some, but not all, of the anomaly, said Dr. Andrew Pavia, chief of pediatric infectious disease at University of Utah Health and director of epidemiology at Intermountain Primary Children’s Hospital.

“Masking, handwashing and physical distancing clearly played a major role, but it is hard to understand why RSV just did not show up at all this year,” Dr. Pavia said. “It’s a silver lining of the pandemic, but also bit of a mystery.”

RSV is a seasonal respiratory illness that causes infection in the lungs and breathing passages. It is often more serious for babies and young children, especially if it causes bronchiolitis or another complication, said Dr. Per Gesteland, a pediatric hospitalist at University of Utah Health and Intermountain Primary Children’s Hospital.

“In Utah, RSV is most active in the winter and early spring, and epidemics are reported every year between January and March,” said Dr. Gesteland, who oversees GermWatch, a tool created by Intermountain Healthcare and University of Utah Health to help the public understand Utah communicable disease trends, symptoms and general information about treatment.

“We’ve never had a year with so few cases of RSV or influenza,” Dr. Gesteland added.

It is not unusual to diagnose well over 100 cases of RSV and influenza per week for several weeks each winter. Some winters are even more severe.

Typically, about 80 children are admitted to Primary Children’s Hospital each week during the January and February peak of respiratory viral season, with up to one-third of those patients requiring ICU care, Dr. Gesteland said.

In the 2018-2019 flu season, about 300 children were hospitalized due to complications with flu, Dr. Gesteland said.

Primary Children’s caregivers had been concerned that a winter RSV and flu surge on top of COVID-19 cases could stretch hospital resources to the brink. Instead, there have been enough resources to treat children with COVID-19 and its related serious complication, Multi-System Inflammatory Syndrome in Children (MIS-C).

RSV is not as transmissible as COVID-19, so measures like masking and reducing social interactions for infants are probably even more effective for RSV. Perhaps the COVID-19 dominance of the viral ecosystem has an additional impact on displacing RSV in ways we do not fully understand, Dr. Pavia said.

The months after the pandemic subsides, however, are a mystery. Will RSV and flu come back stronger than usual? Or less strong? 

“Generally, having a large cohort of infants and young children with no immunity to RSV would signal that when it returns, it will do so with a vengeance, but we are in uncharted territory,” Dr. Pavia said.

Influenza is even harder to predict, and influenza experts don’t like to predict year-to-year variation, Dr. Pavia said.

“One thing seems to be clear from the experience of the winter of 2020-21: We can decrease the impact of influenza on infants and children with better handwashing, mask use, and limiting the amount of their exposure to others,” Dr. Pavia said. “Whether and how we will change our winter behavior enough in the future to reduce the impact of RSV and flu in the future is yet another mystery.”


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