Quantifying the Protection Gap: Respiratory Syncytial Virus Activity Outside the Recommended Prophylaxis Administration Window

INTRODUCTION

Long-acting monoclonal antibodies for respiratory syncytial virus (RSV) prevention, including nirsevimab and the recently approved clesrovimab, are recommended for all infants less than 8 months of age entering their first RSV season, with administration advised from October through March in most of the continental United States.^1,2 This recommendation is based on historical RSV seasonality data and operational simplicity³; however, the granular data available in the post-COVID era shows the epidemiology of RSV is highly variable.⁴ While current guidance acknowledges flexibility based on local epidemiology,¹ state Medicaid and Vaccines for Children programs, which cover most eligible infants, generally adhere to this fixed administration window. However, the fraction of RSV burden falling outside this window has not been quantified using contemporary national surveillance data. Therefore, we analyzed national syndromic and hospital surveillance data to quantify RSV activity outside the October-March window and characterize geographic variability.

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