# P-533. Inpatient Burden of Respiratory Syncytial Virus, COVID-19, or Influenza in the United States Among Children < 5 Years of Age

## TL;DR

This study compares the hospital burden of RSV, COVID-19, and influenza in children under 5 in the U.S., finding RSV leads to more severe outcomes than the other two.

## Contribution

The study provides the first comparative analysis of inpatient burden between RSV and both COVID-19 and influenza in young children.

## Key findings

- RSV was associated with higher risks of supplemental oxygen use, ICU admission, and mechanical ventilation than both COVID-19 and influenza.
- Children under 1 year old had the highest risk of severe outcomes compared to older age groups.
- In-hospital mortality was highest for COVID-19, but RSV and influenza had lower but still significant mortality rates.

## Abstract

Respiratory syncytial virus (RSV), COVID-19 and influenza are leading causes of acute respiratory illness in children. COVID-19 has been shown to have greater inpatient burden than influenza among children age < 5 years, however the comparative burden with RSV is unknown.

We defined a retrospective cohort of children age < 5 years hospitalized for RSV or influenza (April 2019 – March 2020, given disruptions in circulation during the COVID-19 pandemic), or COVID-19 (April 2021 – July 2023). We used PINC-AI Healthcare Database, which contains deidentified hospital records covering ∼25% of admissions in the United States. Outcomes of interest were length of stay (LOS), supplemental oxygen use, intensive care unit (ICU) admission, invasive mechanical ventilation (IMV) and in-hospital mortality. Adjusted risk ratios (aRR) with 95% confidence intervals (CI) were estimated using weighted robust Poisson regression to compare RSV to COVID-19 and RSV to influenza.

We identified 33,644 hospitalized children (19,015 RSV; 10,316 COVID-19; 4,313 influenza). In weighted models to reduce potential confounding, risk of supplemental oxygen, ICU admission and IMV remained higher with RSV than either COVID-19 or influenza in children < 5 years. As compared with COVID-19, RSV was associated with > 2-fold increased risk of supplemental oxygen use (aRR 2.34, 95% CI 2.21-2.47) and a more than 1.5-fold higher risk of IMV (aRR 1.56, 95% CI 1.40-1.73). Similarly, in comparison with influenza, patients hospitalized for RSV had a higher risk of all measures of healthcare resource utilization. In subgroup analyses (aged < 1; 1 and 2-4 years), risks remained elevated, particularly for children aged < 1 year, as compared to older age groups. In-hospital mortality with COVID-19 occurred for 0.5% of patients, compared to RSV (0.1%) or influenza (0.3%).

Risks for in-hospital resource utilization were higher with RSV than either COVID-19 or influenza in adjusted analyses. In-hospital death was greater for COVID-19 than RSV or flu. The severe outcomes observed in this study underscore the need for preventive measures such as maternal and childhood vaccination as well as monoclonal antibodies.

Kathleen M. Andersen, PhD, MSc, Pfizer Inc.: Employee of Pfizer Inc. and may hold stock or stock options Maria D. McColgan, MD, MSEd, Pfizer Inc.: All authors are employees of Pfizer Inc. and may hold stock and/or stock options of Pfizer Inc. Maya Reimbaeva, MS, Pfizer Inc.: All authors are employees of Pfizer Inc. and may hold stock and/or stock options of Pfizer Inc. Tara Ahi, MPH, Pfizer Inc.: Employee of Pfizer Inc. and may hold stock or stock options Mary M. Moran, MD, Pfizer Inc.: Employee of Pfizer Inc. and may hold stock or stock options Alejandro D. Cane, MD, PhD, Pfizer Inc.: All authors are employees of Pfizer Inc. and may hold stock and/or stock options of Pfizer Inc. Santiago M.C. Lopez, MD, Pfizer Inc.: Employee of Pfizer Inc. and may hold stock or stock options|Pfizer Inc.: Stocks/Bonds (Public Company)