Health · Public Health & Disease · 4 hrs ago
Early flu season brings a mutated strain, but vaccination can still help
Flu appeared unusually early in the US this year, with cases first reported on the West Coast about two and a half months ahead of the usual timing.
The CDC says flu activity is still low, but it expects infections to rise as the virus spreads across the Midwest and East Coast.
The main strain is a mutated form of H1N1, and early research suggests people under 25 may have less immunity to it.
There is no evidence that this mutation makes the virus more likely to cause severe illness.
This season’s vaccine is a weaker match because the mutation emerged after experts chose the strains for the vaccine.
Vaccination can still help prevent severe illness, hospitalisation and death, even if it offers less protection against infection.
The available information does not say what happens next beyond the CDC’s expectation that infections will keep rising in the coming weeks.
Influenza arrived about two and a half months earlier than normal on the US west coast, and the CDC expects infections to rise in the coming weeks.
The dominant strain is an H1N1 virus with a mutation called G155E.
The mutation has not been shown to make the virus more likely to cause severe illness, but early research suggests people under 25 may have less immunity to it.
This year’s vaccine was developed before the mutation emerged, making it a weaker match against infection.
Experts say vaccination can still help protect against severe illness, hospitalisation and death.
- Who
- People in the United States affected by flu, including young people who may have less immunity to the strain.
- What
- Flu season began early, and the dominant H1N1 strain has a G155E mutation. This year’s vaccine is a weaker match, but experts say it can still protect against severe outcomes.
- When
- The 2026-27 flu season; the article was published on 9 November 2026.
- Where
- The United States, where flu appeared early on the west coast and was spreading through the Midwest and east coast.
- Why
- The reason for the early season is not fully understood. The vaccine is a weaker match because the variant emerged after the strains for the vaccine had been chosen.
This story does not have two clearly opposing sides.
The WHO brings together experts to review global flu data and forecast which variants may dominate the northern hemisphere in the coming winter.
The G155E variant emerged, making the vaccine a weaker match against infection.
Flu appeared on the west coast about two and a half months earlier than normal.
The Guardian published its report on the early flu season and this year’s vaccine.
- Dominant strain
- H1N1 with the G155E mutation
- Early arrival
- About two and a half months earlier than normal on the west coast
- Recorded hospitalisations
- 16,000 flu-related hospitalisations so far
- Current-season paediatric deaths
- One reported US paediatric influenza-associated death
- 2025-26 flu deaths
- An estimated 24,000 people, including 198 children
What people are saying
about two and a half months earlier than normal
having your seatbelt attached against the flu. It protects you against severe disease, hospitalization, and death.
there’s not a completely ironclad explanation for why this has occurred
This particular variant really emerged after we already had chosen what was in the vaccine