How Has the Disappearance of Influenza B/Yamagata Altered the Proportion of Influenza A and B Cases? Early Findings From Post-COVID Pandemic Global Surveillance Data

We studied worldwide influenza surveillance data (2022–2024), particularly in 145 countries and 260 country-seasons: influenza A represented 77.2% of identified cases, rising from 72.5% prepandemic, with A-dominated seasons increasing from 84.6% to 92.3%. During the same period, B/Yamagata was not detected and uncharacterized B cases dropped from 21.0% to 7.5%, possibly reflecting improved surveillance efforts. These results highlight postpandemic changes in influenza circulation and have important implications for vaccine composition, virus monitoring, and global prevention strategies.