RSV hospitalizations quadrupled among young children after COVID-19

Children aged 2 – 5 years old were nearly 5 times more likely to be hospitalized due to respiratory syncytial virus (RSV) in 2022 than from anytime between 2015 – 2019, according to new findings.

A team of investigators in Colorado reported nationally-representative cohort data showing that the rate of US pediatric RSV and bronchiolitis hospitalizations increased both significantly and with atypical seasonality shortly following the COVID-19 pandemic. A number of factors may be influencing the concerning trend of severe RSV cases among children—though a primary one may be the increasing rate of testing for the respiratory virus in recent years.

A pair of investigators—Robert J. Suss, MPH, of the department of pediatric infectious diseases at University of Colorado School of Medicine and Children’s Hospital Colorado, and Eric A. F. Simões, MBBS, DCH, MD, of the center for global health, department of epidemiology at Colorado School of Public Health—sought to determine age-specific trends in RSV hospitalization before and after the COVID-19 pandemic among children <5 years old. They noted that international research following the pandemic’s beginning in 2020 has already shown a shift in the epidemiological characteristics of the RSV season.

Multiple countries in each of Europe, South America, Asia and Africa have reported a delayed onset of the first post-pandemic RSV season, with many investigators citing the use of nonpharmaceutical interventions as a cause for the delay.

“Taken as a whole, the literature suggests a potential shift in RSV burden toward older children since 2020. It has been suggested that pandemic disruption created an increased susceptibility among older children who have had no prior exposure to endemic viruses, including RSV,” Suss and Simões wrote. “The Centers for Disease Control and Prevention (CDC) reported in early 2023 that the 2022 RSV season occurred later than that of 2021 but still earlier than in pre-pandemic seasons; although this may suggest a return to pre-pandemic seasonality, the CDC warns of potential off-season resurgences in the future.”

The pair conducted their analysis using patient data from the Pediatric Hospital Information Systems from the Children’s Hospital Association. Cases of RSV and non-RSV bronchiolitis were identified through ICD-9 and ICD019 codes. Patients with bronchiolitis were only included in the cohort if they did not also have an RSV diagnosis.

Patients were categorized into 4 age cohorts: 0 – 5 months; 6 – 11 months; 12 – 23 months; 24 – 59 months. Observed patient encounters occurred between June 2015 – March 2023. The team determined RSV seasonality through CDC practices.

Suss and Simões observed 348,077 cases of RSV and 575,984 cases of non-RSV bronchiolitis among children aged 2 - <5 years old from 2015 – 2022. Median patient age was 8 months, with a median hospitalization stay of 1 day. A majority (58.0%) of patients were male. Approximately half (49.8%) of children were White, though 13.0% were determined as unspecified race and 5.4% had missing race data. Children with RSV were more than 2-fold likely to be admitted to the intensive care unit (ICU) than children with bronchiolitis (19.7% vs 8.6%).

The pair observed an overall shift of RSV seasonality toward the summer in 2021. “Although seasonal timing began to shift back to a more typical pattern (eg, occurring in colder months) in 2022 to early 2023, the number of cases in children younger than 5 years was higher overall during this season,” they wrote. “Notably, however, the peak of the RSV season occurred much earlier in 2022 to 2023 than before 2020 (ie, from September to November rather than from December to January as previously evident).”

Children less likely to be diagnosed with bronchiolitis and more likely to be diagnosed with RSV in 2021 – 2022 than 2015 – 2019 in each of the 4 age groups. Children aged 12 – 23 months were nearly 4 times as likely to be hospitalized for RSV in 2022 than 2015 – 2019 (incidence rate ratio [IRR], 3.90; 95% CI, 3.81 – 3.98). The likelihood was even greater among children aged 24 – 59 months old (IRR, 4.86; 95% CI, 4.75 – 4.98), and still nearly doubled among infants aged 0 – 5 months (IRR, 1.77; 95% CI, 1.74 – 1.80).

Investigators additionally noted that boys were up to 53% more likely to be hospitalized than girls for RSV across all years studied, though no other demographic disparities were significantly distinct.

The findings align with sentiments regarding the recent burden of RSV in younger children expressed by experts to Contempory Pediatrics. In one such conversation with editor in chief Tina Tan, MD, FAAP, FIDSA, FPIDS, the Feinberg School of Medicine professor of pediatrics said even 2023 was privy to “several surges” of pediatric RSV outbreaks that were abnormal in nature.

“RSV normally occurs between October and March here in the United States, and for reasons that are still not understood, we actually had several surges last year—with one surge actually occurring during the summer,” Tan told Contemporary Pediatrics. “But it was the fall surge which started earlier that really was incredible, because we also were having surges of influenza as well as COVID, and what that ended up doing was it overwhelmed the pediatric health care system so that there really were few to no hospital beds that were available at any given time.”

Indeed, Suss and Simões concluded their cohort analysis showed an increased burden of pediatric RSV and non-RSV bronchiolitis among hospital settings in 2021—and a nearly doubled burden just the next year.

“Older children had absolute increases in (health care resource utilization) and disease severity, regardless of increases in testing in that population,” they wrote. “This finding has implications for newly available prevention strategies (eg, monoclonal antibodies), for which older children are not currently eligible.”

References

1. ^{Suss RJ, Simões EAF. Respiratory Syncytial Virus Hospital-Based Burden of Disease in Children Younger Than 5 Years, 2015-2022. JAMA Netw Open. 2024;7(4):e247125. doi:10.1001/jamanetworkopen.2024.7125}
2. ^{Fitch J. Reviewing the 2023 RSV season and an outlook on 2024. Contemporary Pediatrics. Published January 2, 2024. https://www.contemporarypediatrics.com/view/reviewing-the-2023-rsv-season-and-an-outlook-on-2024}