Postpandemic Surge: Study Reveals Sharp Increase in Older, Sicker Children Among Hospitalized RSV Cases

After the COVID-19 pandemic subsided, children who were hospitalized for respiratory syncytial virus infections were older and sicker, according to a cross-sectional study conducted by Harvard researchers.

The explanation for the pattern is uncertain, but the researchers have a theory.

The research team was composed of critical care physicians working in pediatric intensive care units at Boston Children’s Hospital, led by Zachary Winthrop, M.D., a fellow in critical care medicine at Boston Children’s Hospital and clinical fellow of critical care at Harvard Medical School, and Melody Duvall, M.D, Ph.D., an assistant professor of anesthesia at Harvard Medical School.

“The genesis of our study came from our observations caring for children admitted to our ICU and managing medical transport calls for children throughout New England during the 2022-23 post-pandemic RSV season,” Winthrop said. “Compared to previous RSV seasons, there was a huge increase in the number of children who needed hospitalization and intensive care than in typical RSV seasons and our hospitals were filled to capacity with these patients.”

The researchers observed that RSV patients seemed to be older and sicker than usual, requiring advanced respiratory support and intensive care.

“We wondered if something about the COVID-19 pandemic had altered the pediatric patient population infected with RSV,” said Duvall.

In their cross-sectional study of 288,816 children 5 years or younger from 48 U.S. pediatric hospitals, the study authors saw a surge in RSV infections during the 2022 to 2023 postpandemic season, with a 70% increase in children requiring advanced respiratory support. The children requiring respiratory support during the surge were older and had fewer comorbidities than in prepandemic seasons.

Winthrop noted that during the pandemic, public health measures to prevent the spread of COVID-19, such as social distancing and masking, also prevented the spread of other viruses, and RSV nearly disappeared during the pandemic.

“Children who normally would be infected with RSV in the first year or two of life escaped early life RSV infection during the pandemic,” he said. “Our study and others found that older children required hospitalization in the postpandemic 2022-23 RSV season. While there were certainly many factors that contributed to the increased rate of respiratory support needs in older, previously healthy children during the 2022-2023 postpandemic season, these findings align with the proposed hypothesis that an immunity debt may be to blame.”

“Immunity debt,” he explained, is the concept that children who evaded RSV infection in their first years of life during the early COVID-19 pandemic did not develop protective immune responses from RSV infection and were experiencing their first RSV infection at an older age contracting more severe infections.

“It is well established that children with comorbidities including congenital heart disease, lung disease, and prematurity are more severely impacted by RSV infection and have more morbidity and higher mortality than healthy children,” Duvall said. “While we can only hypothesize why more previously healthy children were hospitalized with RSV during the 2022-23 season, it is likely due at least in part to the fact that children experience their first RSV infection at an older age postpandemic and not having developed a previous protective immune response were more ill with RSV.”

Furthermore, the researchers concluded that the postpandemic surge of RSV in both vulnerable, younger populations and older, previously healthy children led to substantial increases in U.S. hospital volumes and healthcare system burden.

“Although these trends need to be evaluated in subsequent years, this study highlights possible epidemiologic shifts and trends in respiratory support use that may help inform guidelines and expanded age considerations for new RSV vaccines as they become more widely available,” Winthrop said.