An early start to the season

Flu cases on the US west coast are climbing months earlier than normal, and health experts are stressing the importance of the annual vaccine. Flu activity typically ramps up in December and peaks in February, which makes the current October climb unusual.

A new H1N1 mutation

Several experts have credited the early seasonal start to a new mutation of the influenza A strain H1N1 - the same strain that was behind the 2009 swine flu pandemic.

According to cdc flu data:

• •H1N1 made up 242 of the 300 influenza viruses that public health laboratories have reported to the CDC so far.

The numbers by state

The state-level figures show how sharply the early flu season differs from recent years:

• •California flu positivity hovered slightly above 1% in early October during the past two seasons; as of 10 October, that rate is 9.65%, per the state health department.
• •As of 11 October, Utah had recorded 242 influenza A cases, up from 10 cases this time last year, per Germ Watch, an Intermountain Health database.
• •Parts of central Oregon have also seen an influenza A surge.

What the vaccine covers

The American Medical Association says influenza vaccines can reduce severe illness and hospitalization and recommends flu shots for everyone 6 months and older. The flu vaccine 2026-27 formulation, approved by the FDA in August, targets H1N1, H3N2 - the dominant strain last flu season - and one influenza B virus.

On how well the shots fit the strains now spreading, Scott Hensley, a microbiologist at the University of Pennsylvania, said the match looks close for most of the formula, judging two of its three components a strong fit to what is circulating. He also noted the H1N1 mutation might affect antibodies in younger people.

Scott Hensley's advice: "it is probably a good idea to get vaccinated early".

With positivity climbing and H1N1 dominating reported viruses, Hensley's advice is early vaccination, ahead of a season that typically peaks in February.