Interim Estimated Effectiveness of 2025-2026 COVID-19 Vaccines in Adults Using a Test-Negative Design

What was the estimated effectiveness of 2025-2026 COVID-19 vaccines against medically attended COVID-19 among adults aged 18 years or older in the US from September to December 2025?In this case-control study of 85 725 emergency department and urgent care (ED/UC) encounters and 26 073 hospitalizations in immunocompetent adults aged 18 years or older with a COVID-19–like illness, estimated effectiveness of 2025-2026 COVID-19 vaccination was 50% against COVID-19–associated ED/UC encounters and 55% against COVID-19–associated hospitalization, compared with not receiving a 2025-2026 vaccine dose.This study found that 2025-2026 COVID-19 vaccines were associated with additional protection against medically attended COVID-19 beyond individuals’ existing immunity, suggesting that adults can reduce their likelihood of severe COVID-19–associated outcomes by obtaining a 2025-2026 COVID-19 vaccination.

Corresponding Author: Ruth Link-Gelles, PhD, MPH, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Rd NE, MS H24-9, Atlanta, GA 30329 (hzt7@cdc.gov).

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