Flu cases rise on west coast earlier than usual as US health experts encourage vaccine
California flu test rate at 9.65%, higher than normal 1% rate for early October, amid mutation of H1N1 influenza A strain Flu cases on the west coast are on the rise months earlier than normal, prompting US health experts to stress the importance of the annual vaccine. Flu activity typically ramps up in December, hitting its peak in February. But this season has kicked into action earlier this year, with higher…
Key points
- Flu cases on the US west coast are rising months earlier than usual this season.
- California's flu test positivity rate is 9.65% as of 10 October, versus about 1% in early October in past seasons.
- Experts link the early start to an H1N1 mutation and urge early vaccination.
Flu activity on the west coast has begun months earlier than normal, prompting US health experts to emphasize the importance of the annual flu vaccine. Flu usually ramps up in December and peaks in February, but this season has started sooner, with higher positive case counts than usual.
Several experts attribute the early seasonal start to a new mutation of the influenza A strain H1N1, the strain behind the 2009 swine flu pandemic. That strain accounts for 242 of 300 influenza viruses reported by public health laboratories to the Centers for Disease Control and Prevention to date.
Rates in western states
In California, influenza test positivity was slightly above 1% in early October during the past two flu seasons. As of 10 October, the rate is 9.65%, according to the state's department of health.
As of 11 October, Utah has recorded 242 influenza A cases, up from 10 at this time last year, according to Germ Watch, an Intermountain Health database. Parts of central Oregon have also seen an influenza A surge.
it is probably a good idea to get vaccinated early
— Scott Hensley
Vaccine guidance and promotion
The American Medical Association says flu vaccines can reduce severe illness and hospitalization and recommends shots for everyone 6 months and older. The 2026-27 vaccines, approved by the FDA in August, target H1N1, H3N2 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 well matched to circulating strains. He said the H1N1 mutation might affect antibodies in younger people and that "it is probably a good idea to get vaccinated early". Promotion of flu shots has been reduced under US health secretary Robert F Kennedy Jr, a longtime anti-vaccine activist who has overhauled long-standing childhood vaccine schedules.
