# Flu activity starts early with mutated H1N1 strain

> U.S. flu season begins unusually early as a mutated H1N1 strain spreads.
- Title: Flu activity starts early with mutated H1N1 strain | Shortify
- Summary: U.S. flu season begins unusually early as a mutated H1N1 strain spreads. The 2026-2027 flu season started early with a mutated H1N1 strain causing 1.7…
- Keywords: flu activity, h1n1 strain, cdc, 2026-2027 flu season, mutated virus, influenza, vaccines, hospitalizations, deaths, antivirals, NBC Bay Area
- Source: NBC Bay Area — https://nbcbayarea.com/news/national-international/flu-activity-early-year-mutated-h1n1-strain/4172416
- Published: 2026-11-08T17:32:49+00:00
- Read time: 2 min
- Topics: flu activity, h1n1 strain, cdc, 2026-2027 flu season, mutated virus, influenza, vaccines, hospitalizations, deaths, antivirals, news, local
## Flu activity ramping up early
Flu activity is surging earlier than usual as an influenza A H1N1 strain with a new mutation spreads across the U.S.
## Early flu season start
As of Nov. 5, flu infections are growing or likely growing in 42 states, according to the latest estimates from the U.S. Centers for Disease Control and Prevention.
## 2026-2027 flu season data
So far this season, there have been at least 1,700,000 illnesses, 25,000 hospitalizations and 1,400 deaths from the flu in the U.S., per the CDC.
## H1N1 strain dominance
H1N1, a type of influenza A virus, is currently fueling the vast majority of cases. That’s a shift from last winter, when influenza A H3N2 subclade K (aka, the "superflu") was the dominant strain nationwide.
## New mutation identified
The H1N1 strain circulating in the U.S. has picked up a new mutation which may affect its ability to evade pre-existing immunity, experts say.
## H1N1 history
If H1N1 sounds familiar, that’s because it’s the infamous "swine flu" virus that caused a pandemic in 2009.
## CDC flu activity report
The CDC said in its FluView surveillance report for the week ending Oct. 31: "Early-season influenza activity is currently higher than typically observed at this time of year."

> Early-season influenza activity is currently higher than typically observed at this time of year
## Early flu symptoms
Common flu symptoms include fever, chills, fatigue, body aches, runny nose and coughing.
## Antivirals for treatment
Antivirals can lessen symptom severity and duration, especially for high-risk groups including people over 65, children under 5, and immunocompromised individuals.
## Vaccine availability
The 2026-2 2027 flu vaccines are available at most pharmacies, doctors’ offices and clinics, protecting against three viruses: influenza A H1N1 (pdm09), influenza A H3N2 and influenza B.
## Vaccine timing advice
The best time to get the flu shot is before the end of October, but the vaccine will still provide protection if you get it later in the season.
## H1N1 mutation details
The mutation was first identified in September in Seattle, Washington, according to a preprint paper published to bioRxiv.
## Vaccine effectiveness
Even if the H1N1 strain circulating does not match the one included in the 2026-2027 flu vaccines, the shot is still expected to provide protection.
## Flu season outlook
It’s too early to tell how the 2026-2027 flu season will pan out, or whether it’ll be milder compared to last year’s season.
## Key takeaway

The 2026-2027 flu season started early with a mutated H1N1 strain causing 1.7 million illnesses, 25,000 hospitalizations and 1,400 deaths in the U.S.