California reports 9.65% flu test positivity as West Coast activity rises early

Utah recorded 242 influenza A cases by October 11, up from 10 last year

State health department data put California’s flu test positivity at 9.65% as of October 10. During the past two flu seasons, positivity hovered slightly above 1% in early October.

Germ Watch, an Intermountain Health database, counted 242 influenza A cases in Utah as of October 11, compared with 10 at the same point last year. Parts of central Oregon also saw an influenza A surge.

Flu activity typically ramps up in December and peaks in February. This season began earlier, with more positive cases than normal, and the early rise prompted US health experts to stress the importance of the annual vaccine, The Guardian reported.

Several experts credited the early seasonal start to a new mutation of the influenza A H1N1 strain, which was behind the 2009 swine flu pandemic. The mutated strain accounted for 242 of the 300 influenza viruses that public health laboratories had reported to the Centers for Disease Control and Prevention to date, according to figures cited by The Guardian.

The FDA approved the 2026-27 flu vaccines in August. They target H1N1, H3N2—the strain dominant last flu season—and one influenza B virus. Scott Hensley, a microbiologist at the University of Pennsylvania, said two of the three vaccine components appear very well matched to circulating flu strains.

Hensley also said the H1N1 mutation might affect antibodies in younger people. With flu season picking up, he said in an email: “it is probably a good idea to get vaccinated early”

The broader appeal from health experts was for the importance of annual vaccination. The American Medical Association separately said influenza vaccines can reduce severe illness and hospitalization and recommends flu shots for everyone six months and older.

The Guardian reported that promotion of flu shots has been reduced under US health secretary Robert F Kennedy Jr. The outlet described Kennedy as a longtime anti-vaccine activist and said he had engineered an overhaul of long-standing childhood vaccine schedules.

Reuters contributed reporting to the account.