West coast flu cases rise months early as US experts urge vaccination
A mutated H1N1 strain is driving an unusually early start to the US flu season, with California, Utah and Oregon reporting surges.
At a glance
- Flu cases are rising on the US west coast months before the usual December start to the season.
- A mutated H1N1 strain accounts for 242 of 300 influenza viruses reported to the CDC so far.
- Experts say two of three components in this season's vaccine match circulating strains well.
Flu cases are climbing on the US west coast far earlier than normal, prompting US health experts to stress the importance of the annual vaccine. Flu activity typically ramps up in December and peaks in February, but this season has kicked into action sooner, with higher positive cases than normal recorded.
Positivity jumps in California
California's influenza test positivity hovered slightly above 1% in early October during the past two flu seasons. As of 10 October, that rate stands at 9.65%, according to data from the state's department of health.
Utah has recorded 242 influenza A cases as of 11 October, up from 10 cases at this time last year, according to Germ Watch, an Intermountain Health database. Parts of central Oregon have also seen an influenza A surge.
A mutated H1N1 strain
Several experts have credited the early seasonal start to a new mutation of the influenza A strain H1N1, which was behind the 2009 swine flu pandemic. This strain has accounted for 242 of the 300 influenza viruses reported by public health laboratories to the Centers for Disease Control and Prevention to date.
What the vaccine covers
Influenza vaccines can reduce severe illness and hospitalization, according to the American Medical Association, which recommends flu shots for all people 6 months and older.
The 2026-27 flu vaccines, approved by the FDA in August, target H1N1, H3N2 – the dominant strain last flu season – and one influenza B virus.
Scott Hensley, a microbiologist at the University of Pennsylvania, said two of the three components of this year's vaccine appear to be very well matched to circulating flu strains. However, the H1N1 mutation might affect antibodies in younger people, and with flu season picking up steam, "it is probably a good idea to get vaccinated early", Hensley said via email.
Reduced promotion of shots
Promotion of flu shots has been reduced under US health secretary Robert F Kennedy Jr, a longtime anti-vaccine activist who has engineered an overhaul of long-standing childhood vaccine schedules.
Source: The Guardian.
Questions and answers
- Why is flu season starting early this year?
- Several experts attribute the early start to a new mutation of the influenza A strain H1N1, the strain behind the 2009 swine flu pandemic. It accounts for 242 of 300 influenza viruses reported to the CDC to date.
- Should I get a flu shot now?
- The American Medical Association recommends flu shots for everyone 6 months and older. Microbiologist Scott Hensley said that with flu season picking up steam, it is probably a good idea to get vaccinated early.
- What strains do this season's flu vaccines target?
- The 2026-27 vaccines, approved by the FDA in August, target H1N1, H3N2 – the dominant strain last flu season – and one influenza B virus.
