BY THE OPTIMIST DAILY EDITORIAL TEAM

Flu season usually builds in late fall, but this year it’s getting a jump start. During the week ending September 26, 3.4 percent of respiratory samples tested by clinical labs came back positive for flu, according to CDC data. That’s roughly seven times the rate at the same point last year, when 0.5 percent tested positive.

The early uptick is concentrated in Western states. In Washington, the share of emergency department visits diagnosed as flu climbed from 0.25 percent in late August to 1.34 percent in the week ending October 3, a more than fivefold increase in six weeks. California and Arizona are seeing elevated activity too. “This particular year, it appears to be starting early — like right now,” said Dr. William Schaffner, a professor of preventive medicine and infectious diseases at Vanderbilt Health, who says patients at clinics in his area are already testing positive.

Where flu is showing up so far

Flu starting in the West isn’t unusual or predictive. “There’s nothing unusual about flu starting in the West Coast and moving east,” Schaffner said. It can start almost anywhere; recent seasons have come out of the Southeast or Midwest first. An early start also doesn’t mean a bad season. The CDC’s 2026-2027 outlook projects moderate severity, though with only low-to-moderate confidence.

H1N1 is leading the season so far

Seasonal flu comes in three subtypes: two influenza A strains (H1N1 and H3N2) and one influenza B lineage called Victoria. Of the influenza A samples subtyped during the week ending September 26, 96 percent were H1N1. Last season a fast-spreading H3N2 variant dominated, and the CDC classified 2025-2026 as highly severe for children, with at least 195 child deaths from flu-related causes.

Schaffner describes influenza A and B as siblings: “They’re very related, but they each have their own individual characteristics.” Influenza A tends to drive the biggest outbreaks early; influenza B strains “kind of smolder along” toward the end. The 96 percent figure is where things stand now, not a forecast for the full season.

Flu is, as Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, puts it, “a moving target.” The virus mutates constantly, especially in hemagglutinin, the surface protein it uses to latch onto human cells and the main target of flu vaccines. When circulating strains diverge significantly from those in the vaccine formulation, “that usually predicts a more difficult season,” Offit says. Whether this year’s shot is a close match won’t be clear for weeks.

Why October is the right time to vaccinate

The CDC recommends annual flu vaccination for everyone six months and older. Flu hits hardest in children under five, adults 65 and older, people with chronic health conditions, and pregnant people; tens of thousands of Americans die of flu each season, and serious infections can cause pneumonia, sepsis, and heart or brain complications.

The shot works better when you get it at the right time. The CDC advises against vaccinating in July or August for most adults because protection can wane over a long season. With flu arriving ahead of schedule, “October is the ideal time to get vaccinated, and even more so right now,” Schaffner said. Full protection takes about two weeks to build after the shot.

Effectiveness varies. In terms of flu cases that send people to the doctor, vaccines have been 29 to 56 percent effective over the past decade, per CDC estimates. They do better against severe illness. Schaffner puts the calculus directly: they work best at “keeping you out of the hospital, keeping you out of the intensive care unit, and keeping you out of the cemetery.”

The mRNA flu vaccine approved this season

Adults 50 and older have a new option this year. The FDA approved mFlusiva in August, the first mRNA flu vaccine. Traditional shots contain purified viral proteins. The mRNA version delivers genetic instructions that the body’s cells use to produce those same proteins themselves, then break down. “It cannot influence human genetic material,” Schaffner said. The result, according to Offit: “you’re less likely to get symptomatic disease.”

For adults 65 and older, the CDC still prefers high-dose or adjuvanted shots. Adjuvanted vaccines include an extra ingredient that prompts a stronger immune response.

This article is for informational purposes only and is not meant to offer medical advice.

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