# Flu Season Starts Early with Mutated H1N1 Strain

> Early flu activity in 2026-2027 linked to mutated H1N1 strain spreading rapidly.
- Title: Flu Season Starts Early with Mutated H1N1 Strain · Today
- Summary: Early flu activity in 2026-2027 linked to mutated H1N1 strain spreading rapidly. The 2026-2027 flu season began earlier than usual with a mutated H1N1…
- Keywords: flu, h1n1, cdc, vaccine, 2026-2027, mutated, influenza, season, symptoms, antivirals, vaccination, health
- Source: Today — https://today.com/health/cold-flu/early-flu-season-2026-mutated-virus-spreading-rcna605013
- Author: Caroline Kee
- Published: 2026-10-26T16:50:09.867+00:00
- Read time: 1 min
- Topics: flu, h1n1, cdc, vaccine, 2026-2027, mutated, influenza, season, symptoms, antivirals, vaccination, health
## Flu Season Begins Early
Flu activity in the 2026-2027 season started earlier than typical with rising cases in 44 states.
## CDC Reports Early Surge
The CDC says flu infections are growing or likely growing in 44 states as of Oct. 21, 2026.
## H1N1 Strain Dominates
Influenza A H1N1 is fueling most cases this season, a shift from last winter's H3N2 subclade K.
## New Mutation Detected
The H1N1 strain has picked up a mutation (G155E) identified in September in Seattle, Washington.
## Mutation May Evade Immunity
The mutation could help the virus escape pre-existing immunity, making people more vulnerable.
## H1N1 vs. H3N2 Strain
The H1N1 strain spreading is different from last year's H3N2, which caused the 'superflu' pandemic.
## Early Symptoms Rise
Flu test positivity reached 5.7% during the week ending Oct. 17, 2026, up from less than 1% last year.
## Antivirals for High-Risk Groups
Antivirals are critical for high-risk groups, including those over 65, under 5, and immunocompromised individuals.
## Vaccination Timing
The best time to get the flu shot is before the end of October, but benefits extend into early spring.
## Vaccine Effectiveness
Even with a mismatched strain, the vaccine still provides protection against two other flu strains.
## Why Early Season?
Experts suggest less pre-existing immunity to the mutated H1N1 strain may explain earlier cases.
## What Happens Next?
The CDC warns flu activity may rise further, but the season's severity remains uncertain.
## Key takeaway

The 2026-2027 flu season began earlier than usual with a mutated H1N1 strain, prompting urgent vaccination.