New research suggests the COVID-19 pandemic is responsible for more severe resurgences of respiratory syncytial virus (RSV) in children younger than 5, making them more prone to infection and hospitalization and shifting the disease burden to older children.
Researchers from Colorado used patient data from the Pediatric Hospital Information Systems database from the Children’s Hospital Association to identify cases of RSV and non-RSV bronchiolitis to compare age-specific changes in RSV hospitalization before and after the COVID-19 pandemic.
Of 924,061 children under age 5 included in the study, 348,077 were diagnosed with RSV, and 575,984 were diagnosed with non-RSV bronchiolitis between June 1, 2015, and March 31, 2023. Of those diagnosed with RSV, 187,850 children were hospitalized, admitted to ICU, or visited emergency departments or observational units.
The study found that post-pandemic RSV cases increased for all age groups, but especially among children in the 2- to 5-year-old age group. In contrast, the incidence of bronchiolitis hospitalization decreased or remained unchanged compared to earlier seasons.
Among children under age 5 with RSV in 2022, those who were newborn to 5 months were 1.77 times as likely to be hospitalized compared to the years 2015 to 2019, whereas children 12 to 23 months were 3.9 times as likely to be hospitalized. Children aged 24 to 59 months were 4.86 times as likely to be hospitalized after the pandemic compared to previous seasons.
The risk of hospitalization, emergency department visits, and observation unit admissions increased in volume with age, suggesting a disproportionately increased burden in older children. Additionally, a significantly higher proportion of patients with RSV were admitted to the ICU compared with those who had bronchiolitis.
Although the researchers said the increase in hospital use among those with RSV could be attributed in part to increased testing, research suggests the pandemic created an increased susceptibility to RSV among older children with no prior exposure to endemic viruses like RSV.
RSV Season Shifts Toward Warmer Months
According to the study, the pandemic also shifted the RSV season toward warmer months. For example, the RSV peak season occurred much earlier in 2021, 2022, and 2023 than in 2020. Although seasonal timing began to shift back to a more typical pattern of occurring in colder months in 2022 to early 2023, the number of RSV cases in children younger than 5 years was higher overall during the most recent season.“So RSV causes annual epidemics, but last year, what we were noticing is that there wasn’t just one epidemic, but there were actually several surges of RSV that occurred out of its normal season,” she said.
RSV normally occurs between October and March in the United States each year, but for reasons still not understood, there were several surges in 2023—one during the summer and an “incredible” fall surge, she added.
Masking and Social Distancing May Have Contributed to Surge in RSV
RSV is a leading cause of acute respiratory tract infections in young children, with an estimated 2.1 million outpatient visits and 58,000 to 80,000 hospitalizations in children under 5 years old each year. According to the Centers for Disease Control and Prevention, infants younger than 6 months with underlying medical conditions are most at risk of severe disease, but newborns are relatively protected because they receive maternal antibodies from the placenta.However, because these antibodies wane quickly, infants are most vulnerable to RSV at 1 to 2 months of age, with most children having had RSV by the time they reach their first or second birthday.
Furthermore, the authors suggested nonpharmaceutical interventions such as masking and social distancing during the pandemic may have prevented RSV from spreading and resulted in a susceptible population with diminished immunity to RSV.
