California officials are warning of a new strain of influenza that is causing flu-related cases and hospitalizations to rise across the state, and public health experts across the country are issuing similar warnings.
The newly emerged strain of influenza A, H3N2 subclade K, is already wreaking havoc around the world and affecting California Department of Public Health hospitals and clinics. Announced on Tuesday. The agency said seasonal influenza activity is “on the rise” in the state. The data shows that the flu test positivity rate, which measures the percentage of patients who come to the hospital with flu symptoms and actually test positive for the flu, has increased in recent weeks. However, it is still relatively low compared to last year’s influenza season.
“Influenza really started to increase by mid-December, and infection rates are still rising,” said Dr. Elizabeth Hudson, Kaiser Permanente’s regional chief of infectious diseases. “We expect to see some leveling off in the coming weeks, but the recent holidays have caused a lag in the data and will become clearer over the next week or so.”
Hudson said most influenza-related cases are treated without the need for hospitalization, “but those who are primarily hospitalized are older adults and patients who are at higher risk of complications from the flu.”
According to Data from public health agenciescentral California and the Bay Area have high influenza positivity rates, and areas around Sacramento and Southern California have moderate rates. Influenza infection rates are currently low in rural areas in the northern part of the state, according to the agency’s website.
In Los Angeles County, Recent data from the Department of Health It shows that from the end of last year to the beginning of 2026, there were 162 influenza-related hospitalizations and a further 18 admissions to intensive care.
Nationally, this year’s flu season is much worse than in California. According to Centers for Disease Control and PreventionThis flu season has seen the highest number of cases in the United States in more than 30 years. According to the agency’s estimates, Since late fall, the United States has reported at least 15 million cases, 180,000 hospitalizations and 7,400 deaths. Yvonne Maldonado, Taub Professor of Global Health and Infectious Diseases at Stanford University, said at least two of the deaths were children. in a news release. The state Department of Public Health confirmed that these pediatric influenza-related deaths occurred in California.
Last year, infectious disease experts predicted that this flu season would be particularly harmful to high-risk groups, especially children.Dr. Peter Chin-Hong, an infectious disease expert at the University of California, San Francisco, told the Times that lower flu vaccination rates and “surging variant” flu strains are to blame.
Last year’s flu season was particularly bad, “but this year we had very little idea what was going to happen,” said Dr. Neha Nanda, medical director of antimicrobial stewardship at Keck Medicine at the University of Southern California. Nanda said the number of positive flu cases this season is trending up earlier than usual, but at least in California, it’s not much higher than last year or in years before COVID-19.
Dr. Sam Torbati, co-chair and medical director of the emergency department at Cedars-Sinai Medical Center, said around the second week of December his department saw a number of patients coming in with flu-related illnesses, part of a spike in hospitalizations seen countywide.
He said he couldn’t remember “seeing so many patients so sick.”
“The flu season is still in its early stages and could get much worse,” Torbati said.
Experts believe the strain is now “likely” to mutate and evade immunity from current vaccines. That’s because the strain emerged in late summer, long after health officials had already decided on the formula for flu vaccines.
“Current seasonal influenza vaccines remain effective in reducing severe illness and hospitalizations, including for currently circulating viruses,” said Dr. Erica Pan, director of the state Department of Public Health.
While the flu shot may not prevent death from the flu, it “may reduce the likelihood of severe illness, avoid hospitalization, and shorten the duration of illness,” Dr. Michelle Barron, UCHealth’s senior medical director for infection prevention and control, said in the report. Assn. American Medical College.
Authorities are urging the public, especially those at high risk of severe influenza complications, such as young people and the elderly, to get vaccinated or receive antiviral drugs such as Tamiflu immediately.
The flu can cause very severe symptoms, with symptoms similar to “being hit by a Mack truck,” such as fatigue, fever, cough and body aches, Hudson said.
Symptoms can be more severe in children and other high-risk people.
“Children can become dehydrated [or] “Pneumonia and more severe cases of influenza in children can cause inflammation of the brain and heart,” Hudson said.
The problem is not limited to the United States. Influenza A strain, H3N2 subclade K, caused a severe influenza season in Australia, Japan, UK and other regions of Europe and Asia.