Early Flu Wave Hits Nation With Mutated H1N1

Hospitalizations rose sharply in mid-October as a mutated H1N1 strain drives an early start to the 2026 respiratory season.

Updated on Nov. 2, 2026 in COVID-19

Bold flat-color vector editorial illustration of a clustered group of spiky virus-like forms spreading across an ochre field. — Influenza hospitalizations hit almost 5,000 nationally in the week ending Oct. 17, the highest mid-October rate since 2010-2011, as a mutated H1N1 strain spreads. AI Illustration. Upload story photo >

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Do you plan to get your flu and COVID-19 vaccines this season?

The CDC reported almost 5,000 laboratory-confirmed influenza hospitalizations nationwide during the week ending Oct. 17, the highest early-season rate for mid-October since the 2010-2011 season. The H1N1 variant accounts for most subtyped influenza A viruses and carries new mutations compared with last year's virus.

Why it matters

The new mutations create some mismatch with this season's vaccine, though preliminary CDC data show current vaccine antibodies still recognize the variant. Early hospitalization levels signal a potentially heavy respiratory season for the United States.

CDC surveillance recorded almost 5,000 lab-confirmed influenza hospitalizations nationwide in the week ending Oct. 17, the highest mid-October rate since 2010-2011, with H1N1 making up 125 of 127 subtyped influenza A viruses the week ending Oct. 3. Early vaccine efficacy estimates are not expected until early December, leaving the degree of vaccine protection against the new variant unresolved.

The players

Centers for Disease Control and Prevention (CDC)

The CDC is the federal agency that tracks influenza and COVID-19 activity nationwide and publishes the surveillance data cited in this story.

Vaccine Adverse Event Reporting System (VAERS)

VAERS is the national passive surveillance system co-managed by the CDC and the FDA that collects reports of possible adverse events following vaccination.

The details

Health officials report the mutated H1N1 strain is spreading across the country, with flu activity increasing in the West and South. Preliminary data suggest the current vaccine still generates antibodies that recognize the variant, even as the virus has changed from last year. COVID-19 activity remains low but steady, and home tests can identify influenza, COVID-19 and RSV.

Week ending Oct. 3: H1N1 accounted for 125 of 127 subtyped influenza A viruses
Week ending Oct. 17: almost 5,000 lab-confirmed flu hospitalizations were reported nationwide
Early December: early flu vaccine efficacy estimates are expected
December and January: a COVID-19 surge is expected

Big Picture

The week ending Oct. 17 hospitalization rate was the highest for mid-October since the 2010-2011 influenza season recorded in CDC surveillance. That places the current early wave among the most significant early-season flu activity in the past 15 years.

Adults 50 and older are eligible for the new mRNA influenza vaccine, which can cause body aches and a low-grade fever. Home tests can identify influenza, COVID-19 and RSV, which can help guide decisions about testing and care during the early respiratory season.

The takeaway

Early flu activity this season makes vaccination and prompt testing more relevant than usual. Anyone experiencing flu-like symptoms can use a home test to distinguish influenza, COVID-19 and RSV.