Increasing Predominance of Norovirus GII.17 over GII.4, United States, 2022-2025.

Norovirus GII.17 outbreaks in the United States increased from <10% during the 2022-23 season to 75% during the 2024-25 season, surpassing the number of GII.4 outbreaks. The norovirus season also started earlier in 2024-25 than in previous seasons. Continued norovirus surveillance is needed to detect and monitor emerging strains.