Flu Rising Months Early on the US West Coast as Health Experts Urge Vaccination

Flu cases on the west coast of the United States have begun rising months earlier than normal. Against this unusual early increase, US health experts are stressing the importance of the annual flu 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 positive cases than normal recorded.

Several experts have credited the early seasonal start to a new mutation of the influenza A strain H1N1. The same strain 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 (CDC) to date. In other words, a large share of the circulating virus is this mutated strain.

In California, during the past two flu seasons, influenza test positivity hovered slightly above 1 percent in early October. According to data from the state's department of health, as of October 10 that rate stands at 9.65 percent.

The picture is similar in Utah. According to Germ Watch, an Intermountain Health database, Utah had recorded 242 influenza A cases as of October 11, up from just 10 cases at this time last year. Parts of central Oregon have also seen an influenza A surge.

Influenza vaccines can reduce severe illness and hospitalization, according to the American Medical Association, which recommends flu shots for all people aged six 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 the circulating flu strains.

However, Hensley warned that the H1N1 mutation might affect antibodies in younger people. With flu season picking up steam, he said via email, it is probably a good idea to get vaccinated early.

A political dimension has also come into the discussion. 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, the report noted.

Taken together, the experts' message is clear: the season has started early this year, the numbers show it, and they are emphasising early vaccination as the most effective means of protection.