Flu season starts earlier than usual in parts of the United States, federal surveillance shows. National laboratory testing reported 3.4% of respiratory samples positive for influenza during the week ending Sept. 26, compared with roughly 0.5% at the same point last year, according to CDC data. In a typical year activity builds in October or November and peaks between December and February, but this season’s early climb is already visible in some regions.
The uptick has been concentrated in Western states, where emergency department visits coded as influenza have risen. For example, Washington state saw the share of ED visits diagnosed as flu increase from 0.25% in the week ending Aug. 29 to 1.34% in the week ending Oct. 3, based on CDC emergency department data. Clinicians in areas already seeing positives have described a faster start than in recent seasons.
Laboratory subtyping indicates influenza A currently predominates, with H1N1 representing about 96% of subtyped influenza A samples in the week ending Sept. 26. Last season was marked by a fast-spreading H3N2 subclade and a high burden among children; federal tallies counted 195 pediatric deaths in 2025–2026. The federal outlook for 2026–2027 rates the season more likely to be moderate, but confidence in that forecast is limited. Experts underscore that viral evolution — particularly changes to hemagglutinin, the protein targeted by vaccines — shapes how severe a season becomes and how well vaccines perform.
Vaccination remains the primary preventive measure: annual shots are recommended for everyone aged six months and older, and high-dose or adjuvanted formulations are preferred for adults 65 and older, per CDC guidance. With the season shifting earlier, October is widely cited as an appropriate time to receive the vaccine so protection is in place before cases accelerate; immunity takes about two weeks to peak. Historically, vaccine effectiveness against medically attended illness has ranged roughly 29%–56% across seasons, while protection against severe outcomes is generally higher. A new mRNA option, mFlusiva, was approved in August for adults 50 and older; availability can be checked via Moderna’s locator finder. Whether the early rise becomes a widespread surge will become clearer in the coming weeks as federal surveillance reports track spread beyond initial hotspots.
