Doctors Urge Flu Shots as Unusually Early Season Hits West Coast and New H1N1 Mutation Raises Fears for Young

Doctors are urging Americans 6 months and older to get vaccinated against the flu after an unusually early rise in cases on the West Coast, driven by a strain that scientists say may leave younger people less protected than usual.

The predominant strain this season is H1N1, the virus that caused the 2009 swine flu pandemic and is now a standard component of annual flu vaccines. But this year's version carries a new mutation that virologists are still working to understand.

The early surge comes as flu vaccination rates in the United States have fallen sharply from pre-pandemic levels.

Early and unusual

The share of flu tests coming back positive at clinical labs reached 5% last week, according to data reported to the Centers for Disease Control and Prevention. That is the highest level for this time of year in a decade.

On the West Coast, the positivity rate has climbed to 10.7%, compared with 0.5% at the same point last year. Flu positivity typically peaks at about 30% during the height of the season.

Eight Southern states, including Florida and South Carolina, are also seeing elevated numbers, according to Caitlin Rivers, an epidemiologist at Johns Hopkins University.

The pattern is unusual. Flu seasons in the United States typically begin in the South and spread north. This year, the virus appears to be moving from the West.

"There's no clear reason to me why this would be the case," Rivers said.

CDC data show overall flu activity nationwide remains low but has been rising since late August.

A new mutation

Scientists say the strain itself may help explain the early start.

This season's H1N1 carries a mutation known as G155E. Last flu season was dominated by a different strain, H3N2, meaning many people have not encountered H1N1 recently.

People previously exposed to H1N1 through infection or vaccination retain only residual protection against older versions of the virus. Small studies have found that antibodies from people exposed during last season did not recognize the new mutation, with the effect most pronounced in teenagers and young adults.

Jennifer Duchon, a pediatric infectious disease expert at Mount Sinai Children's Hospital in New York, said the strain "may be more severe" in younger people who have not had much exposure to it.

Jeanne Marrazzo, chief executive of the Infectious Diseases Society of America, noted that the studies were small and said the findings were not cause for alarm.

Vaccine appears well matched

The 2026-27 flu vaccines, approved by the Food and Drug Administration in August, protect against H1N1, H3N2 and one influenza B virus.

Scott Hensley, a microbiologist at the University of Pennsylvania, said two of the three vaccine components appear to be very well matched to circulating viruses.

"It is probably a good idea to get vaccinated early," Hensley said.

Over the past decade, flu vaccines have reduced the risk of hospitalization and death by 30% to 60%, depending on the season.

Falling vaccination rates

The early season comes as fewer Americans are getting flu shots.

About 58 million U.S. adults received a flu vaccine last season, according to health data firm IQVIA, down more than 20% from nearly 75 million in the 2019-20 season. Around half of U.S. children were vaccinated last season, compared with more than 60% in 2019-20, according to CDC data.

Vaccine makers say demand so far this year is in line with last year, and pharmacists told Reuters that vaccination rates have not picked up significantly despite the early rise in cases.

Policy changes under scrutiny

The decline has fueled debate over federal health policy under Health Secretary Robert F. Kennedy Jr., a longtime vaccine skeptic who has overhauled childhood vaccine schedules.

The CDC dropped its recommendation of flu shots for most children at the start of 2025, a change that a court later put on hold. The agency also reportedly pulled its 2025 flu advertising campaign.

Paul Offit, a pediatric infectious disease expert at Children's Hospital of Philadelphia, said the government's pullback on promoting flu shots and Kennedy's own statements had hurt immunization rates.

"He has done what he can to discourage flu vaccination," Offit said.

A spokesperson for the Department of Health and Human Services, Emily Hilliard, pointed to the CDC's respiratory illness guidance, which describes vaccination as the most effective tool against serious illness.

The American Medical Association continues to recommend flu vaccination for everyone 6 months and older.

A heavy toll last season

Last season, an estimated 32 million Americans got the flu, about 390,000 were hospitalized and about 24,000 died, according to estimates.

Health experts say the early start this year gives people a narrow window to get vaccinated before flu spreads widely. It takes about two weeks after vaccination for the body to build protection.

Doctors also advise frequent hand-washing, staying home when sick and seeking medical care quickly for severe symptoms. Antiviral medications can reduce the severity of illness if started early, particularly for people at high risk of complications, including older adults, young children, pregnant women and people with chronic health conditions.