Evaluation of a Novel Data Source for National Influenza Surveillance: Influenza Hospitalization Data in the National Healthcare Safety Network, United States, September 2021–April 2024

<b>Objectives.</b> To evaluate the completeness and utility of influenza hospital data reported to the Centers for Disease Control and Prevention's National Healthcare Safety Network (NHSN) from September 2021 to April 2024. <b>Methods.</b> Acute care and critical access hospitals in the United States reported daily numbers of new hospital admissions of patients with laboratory-confirmed influenza to NHSN during voluntary and mandatory reporting periods. To evaluate the completeness of data reported to NHSN, we compared the number of influenza hospital admissions reported to NHSN with data reported to the Influenza Hospitalization Surveillance Network (FluSurv-NET) among 13 states and overlapping counties reporting to both systems from September 2021 to April 2024. <b>Results.</b> During voluntary reporting, about 77% of US hospitals reported daily influenza hospital admission counts to NHSN; during mandatory reporting, this increased to a mean of 94%. These data were highly correlated (<i>r = </i>0.978; 95% confidence interval = 0.968, 0.985; <i>P</i> < .001) with numbers from FluSurv-NET and in most states (<i>r</i> range = 0.861-0.988) within overlapping surveillance areas. <b>Conclusions.</b> Influenza hospital admissions reported to NHSN demonstrate high levels of complete reporting; overall counts are highly correlated with a high-quality, long-standing influenza hospitalization surveillance system. (<i>Am J Public Health</i>. 2026;116(2):251-255. https://doi.org/10.2105/AJPH.2025.308282).