Flu cases spike early on US west coast, health experts urge vaccination in mutated H1N1 season

California test positivity reaches 9.65% as Utah reports 242 cases, up from 10 last year

By LineZotpaper

Published23 October 2026

Read Time2 min

Flu cases on the American west coast are rising months earlier than normal, driven by a mutation of the H1N1 strain, according to data from state health departments and the Centers for Disease Control and Prevention. Health experts recommend early vaccination as the 2026-27 flu season accelerates.

Flu activity typically ramps up in December and peaks in February, but this season has begun earlier than usual, with positive case counts well above seasonal norms. Several experts have attributed the early start to a mutation of the influenza A strain H1N1, which caused the 2009 swine flu pandemic.

Public health laboratories have reported 242 H1N1 cases out of 300 influenza viruses to the CDC so far this season. In California, influenza test positivity stood at 9.65% as of 10 October, compared with just over 1% at the same time in the past two seasons, according to the state’s department of health. Utah 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 experienced a surge.

The American Medical Association recommends the annual flu shot for everyone aged six months and older. The 2026-27 vaccines, approved by the FDA in August, target H1N1, H3N2 (the dominant strain last season) and one influenza B virus.

Scott Hensley, a microbiologist at the University of Pennsylvania, said two of the vaccine’s three components appear to be well matched to circulating strains. However, the H1N1 mutation may affect antibody response in younger people, and “it is probably a good idea to get vaccinated early”, Hensley said.

Promotion of flu shots has been reduced under US Health Secretary Robert F Kennedy Jr, a longtime anti-vaccine activist who has overhauled childhood vaccine schedules, according to Reuters reporting.

Analysis

Why This Matters

The early flu surge could strain healthcare systems already dealing with respiratory illnesses
A mutated H1N1 strain may reduce vaccine effectiveness in younger populations, raising the importance of early vaccination.
Reduced public promotion of flu shots under the current administration may lower vaccination rates.

Background

Flu seasons on the west coast typically intensify in December and peak in February. The H1N1 strain, which caused the 2009 pandemic, has now mutated. The CDC and state health departments are tracking elevated case counts weeks ahead of schedule.

Key Perspectives

Health experts and CDC: The annual flu vaccine remains the best protection against severe illness and hospitalisation. Dr Scott Hensley notes two of three vaccine components are well matched, but the H1N1 mutation may require extra vigilance.
United States Department of Health and Human Services: Under Secretary Robert F Kennedy Jr, flu-shot advocacy has been reduced and childhood vaccine schedules overhauled, potentially lowering public uptake.

What to Watch

Test positivity rates in California, Utah and Oregon over the next two weeks.
Hospitalisation figures for influenza and COVID-19 co-infections.
Any further changes to federal vaccine recommendations or promotion.

Sources

Flu cases rise on west coast earlier than usual as US health experts encourage vaccine · World news | The Guardian

Checked

11 claims in this story checked against 1 source: 6 supported.

Show each claim

Partly supportedFlu cases are spiking early on the US west coast.World news | The Guardian: “Flu cases on the west coast are on the rise months earlier than normal”
SupportedHealth experts are urging vaccination.World news | The Guardian: “prompting US health experts to stress the importance of the annual vaccine”
Partly supportedThe early flu season is driven by an H1N1 mutation, according to state health department and CDC data.World news | The Guardian: “Several experts have credited the early seasonal start to a new mutation of the influenza A strain H1N1”
SupportedCalifornia flu test positivity was 9.65% as of 10 October.World news | The Guardian: “As of 10 October, that rate is 9.65%, according to data from the state’s department of health.”
SupportedCalifornia positivity was just over 1% at the same time in the past two seasons.World news | The Guardian: “during the past two flu seasons, influenza test positivity hovered slightly above 1% in early October.”
SupportedUtah recorded 242 influenza A cases as of 11 October, up from 10 at that time last year.World news | The Guardian: “As of 11 October, Utah has recorded 242 influenza A cases, up from 10 cases this time last year, according to Germ Watch, an Intermountain Health database.”
Partly supportedPublic health laboratories reported 242 H1N1 cases out of 300 influenza viruses to the CDC.World news | The Guardian: “This strain has accounted for 242 of 300 influenza viruses reported by public health laboratories to the Centers for Disease Control and Prevention to date (CDC).”
Partly supportedHealth experts recommend early vaccination as the season accelerates.World news | The Guardian: “with flu season picking up steam, “it is probably a good idea to get vaccinated early”, Hensley said via email.”
Partly supportedParts of central Oregon have experienced a surge in flu activity.World news | The Guardian: “Parts of central Oregon have also seen an influenza A surge.”
SupportedHensley said, “it is probably a good idea to get vaccinated early”.World news | The Guardian: ““it is probably a good idea to get vaccinated early”, Hensley said via email.”
SupportedThe 2026–27 vaccines target H1N1, H3N2 and one influenza B virus.World news | The Guardian: “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.”