In the week ending Sept. 26, 3.4 percent of respiratory specimens tested at clinical laboratories across the United States were positive for influenza, against roughly 0.5 percent at the same point in 2025. That works out to about seven times last year’s rate, an early start to the 2026-27 flu season by this measure. The Centers for Disease Control and Prevention publishes both figures but does not state the ratio itself.
Activity is still low in absolute terms, and the national outlook is for a moderate season.
The Two CDC Positivity Figures Behind the Ratio
The ratio comes from CDC’s weekly FluView surveillance. The report for week 38, ending Sept. 26, 2026, records 1,151 positive specimens out of 33,547 tested at clinical laboratories, or 3.4 percent. For the matching point last year, the week 39 report, ending Sept. 27, 2025, shows 189 positives out of 39,787 tested, or 0.5 percent. Dividing 3.4 by 0.5 gives 6.8; the raw counts give 7.2. Either way the answer rounds to about seven. The metric is the share of specimens at clinical laboratories that tested positive for influenza, not a count of cases, and the number of specimens tested differs between the two years, which is why the percentages are the fair comparison.
The week before, ending Sept. 20, 2025, ran lower still, at 0.4 percent of 45,194 specimens, and the week ending Oct. 4, 2025 was also 0.4 percent, 208 of 48,237, according to CDC’s week 40 report. Last autumn started from a very low base, which is part of why the multiple looks so large.
Positivity Versus Illness: What the Other CDC Measure Shows
Positivity is not the same as how many people are sick. Outpatient influenza-like illness, which counts visits for fever with cough or sore throat regardless of cause, stood at 1.7 percent of visits in the Sept. 26, 2026 week, barely above the 1.6 percent CDC recorded in the week ending Sept. 27, 2025. CDC notes in its report that several respiratory viruses are circulating, so that indicator does not isolate influenza.
Positivity has kept climbing. The following week’s report, ending Oct. 3, shows 3.6 percent positive, 1,435 of 39,317 specimens, with influenza A accounting for 97.0 percent of positives. Illness visits held at 1.8 percent, below the 3.1 percent national baseline, and every one of the 10 HHS regions sat under its own baseline. Of the jurisdictions on CDC’s activity map, 2 were at low and 53 at minimal.
H1N1 Leads, and the West Started First
The early cases are dominated by one subtype. In the week ending Sept. 26, public health laboratories subtyped 55 influenza A specimens, and 53 were H1N1pdm09 with 2 H3N2, about 96 percent H1N1. By the week ending Oct. 3, 125 of 127 subtyped influenza A viruses, 98.4 percent, were H1N1pdm09.
Live Science’s reporting places the early rise mostly in Western states including Washington, California and Arizona. Dr. William Schaffner of Vanderbilt Health told the outlet the season “appears to be starting early” and that a West Coast start is normal, adding that flu “can start almost anywhere.” Dr. Paul Offit of Children’s Hospital of Philadelphia called flu “a moving target” because the virus mutates, and said a mismatch between circulating strains and the vaccine usually predicts a harder season.
CDC’s Moderate-Season Outlook and the Case for an October Shot
CDC’s 2026-2027 respiratory season outlook, dated Sept. 23, expects a moderate flu season across all ages, with low to moderate confidence, and sees no current evidence that a severe season is likelier than usual. National influenza hospitalizations have typically peaked between December and February. The outlook flags antigenic drift in a predominant subtype as one factor that could produce a higher peak. The 2025-26 season ended with 195 pediatric deaths reported through the week ending Sept. 26 and 198 after the week ending Oct. 3 report added three more.
CDC recommends an annual flu vaccine for everyone 6 months and older, with rare exceptions, and calls vaccination particularly important for people at higher risk of complications. Live Science adds that protection takes about two weeks to reach full strength after the shot, and that over the past decade the vaccine has been 29 to 56 percent effective against flu illnesses that lead to medical care, citing CDC estimates. The CDC outlook puts the toll the shot averts at an estimated 180,000 hospitalizations in the 2024-25 season, while cautioning that uptake and effectiveness may differ from past seasons.
The FluView data do not yet show the early rise in positivity turning into early hospitalizations: outpatient illness visits remain below baseline in all 10 HHS regions, and the Oct. 3 report is the latest CDC had published when this article was written.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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