From Today · Caroline Kee · · 1m 40s
Flu Season Starts Early with Mutated H1N1 Strain
Early flu activity in 2026-2027 linked to mutated H1N1 strain spreading rapidly.
In brief
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 strain, prompting urgent vaccination. Originally reported by Today.
Quick answers
- 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.
- What is the key takeaway from Flu Season Starts Early with Mutated H1N1 Strain?
- The 2026-2027 flu season began earlier than usual with a mutated H1N1 strain, prompting urgent vaccination.
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.
At a glance
The 2026-2027 flu season began earlier than usual with a mutated H1N1 strain, prompting urgent vaccination.
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