Overview
- U.S. surveillance shows flu activity rising earlier and higher than normal with cases growing in most states according to CDC data for the week ending Oct. 17.
- Influenza A H1N1, mostly the D.3.1.1 subclade carrying the G155E mutation, now accounts for the vast majority of samples reported to public-health labs.
- Laboratory and preprint studies report that G155E can reduce recognition by some preexisting human antibodies, which may lower but not eliminate protection from this year’s vaccines.
- Health officials are urging immediate vaccination and fast access to antiviral treatment for people at high risk because antivirals work best when started within 48 hours of symptoms.
- Experts warn younger people may face higher risk this season and that a later H3N2-driven wave remains possible, so the overall season severity and vaccine effectiveness are still uncertain.