Health · Public Health & Disease · 11 hrs ago
H1N1 Overtakes H3N2 in Early US Flu Season
H1N1 has overtaken H3N2 as the dominant flu strain in early US surveillance, after scientists had forecast H3N2 would lead this season.
H1N1, also known as swine flu, caused a pandemic in 2009, and researchers have linked early emergency-room visits to a mutation called G155E.
Flu hospitalizations were 10 times higher in mid-October than in the same week of 2025, though flu activity remained low nationally.
Cases started rising in August, first mainly in the West, and by October 28 infections were growing or likely growing in 39 states, with reports of increased activity on the East Coast.
The mutation may help the virus evade some existing immunity, but it is too soon to know how well the vaccine protects against it.
This season’s vaccine targets H1N1, B/Victoria and H3N2, and is still expected to provide meaningful protection, including against severe illness; researchers will learn more as the season develops.
Early flu surveillance on the US West Coast found H1N1 had overtaken H3N2 as the dominant strain in October.
Flu infections began rising in August, earlier than usual, with early cases concentrated mostly on the West Coast.
In mid-October, flu hospitalizations reached 2.1 per 100,000 people, compared with 0.2 during the same week in 2025.
The CDC estimated that flu infections were growing or likely growing in 39 states as of October 28.
The current flu vaccine targets H1N1, B/Victoria lineage and H3N2, but its protection against the mutated H1N1 strain is not yet known.
- Who
- US residents and health authorities tracking flu activity.
- What
- H1N1 overtook H3N2 as the dominant flu strain in early US surveillance.
- When
- In October 2026; the article was published November 3, 2026.
- Where
- The United States, with early cases mostly on the West Coast.
- Why
- Not stated.
This story does not have two clearly opposing sides.
Flu infections began rising in the United States.
Early West Coast surveillance found H1N1 had overtaken H3N2 as the dominant strain.
Flu hospitalizations were 2.1 per 100,000 people, compared with 0.2 during the same week in 2025.
The CDC estimated that infections were growing or likely growing in 39 states.
- Dominant strain
- H1N1 overtook H3N2 in October
- Hospitalizations
- 2.1 per 100,000 people in mid-October
- Comparison
- 0.2 hospitalizations per 100,000 during the same week in 2025
- Infections growing
- 39 states as of October 28
- Vaccine strains
- H1N1, B/Victoria lineage and H3N2
1 source
What people are saying
A mismatch is not a black-or-white situation. We may have less immunity, not no immunity.