California’s flu season could see an earlier, faster start due to the change

California could see an early start to the annual flu season, as a combination of low vaccination rates and late mutations to the virus may make the state particularly vulnerable to transmission, health experts say.

There are already warning signs. Los Angeles County recently reported its first flu death of the season, and other counties are reporting record-breaking or strong flu seasons ahead of what is expected.

Typically, the flu tends to pop up right before Christmas and New Year’s, but Dr. Elizabeth Hudson, regional physician director of infectious diseases at Kaiser Permanente Southern California, said she expects there may be an increase in viral activity in the next two to three weeks.

“We’re looking forward to a quick and possible start to the flu season,” Hudson said.

Last year’s flu season was California’s worst in years, and it’s not uncommon for bad flu seasons to back to back. But according to Dr. Peter Chen Hong, an infectious disease specialist at UC San Francisco, the decline in flu vaccination rates and the mix of “soaped mutants” are particularly concerning this year.

“It might infect more people. And as more people get infected, some of them will go to the hospital,” said Chen Hong.

The timing of this new flu subtype — called H3N2 subclade K — is particularly difficult. It emerged in late summer, after health officials had already decided how to develop this fall’s flu vaccine, a decision that should have been made in February.

H3N2 subclade K appears to have started to dominate in Japan and the UK, Hudson said.

“There seems to be some difference between the seasonal flu vaccine strains and the new subtypes,” Hudson said.

It is unclear whether subclade K will reduce the effectiveness of this year’s flu shot.

In California and the rest of the United States, “things are quiet, but I think it’s the calm before the storm,” Chen Hong said. “From what we’re seeing in England and Japan, more people are getting the flu earlier.”

Chin-Hong noted that subclade K is not much different than this year’s flu vaccines. And he noted that data recently published in England showed that this season’s vaccine was still effective against hospitalizations.

According to the UK government, vaccinated children are 70% to 75% less likely to need hospital care, and adults 30% to 40% less likely. The UK government says the flu vaccine is generally 30% to 60% effective, and is more effective in young people.

Even if there is some difference between the vaccine and circulating strains, “the flu vaccine still provides protection against serious illness, including hospitalization,” according to the Los Angeles County Department of Public Health.

“Public Health strongly encourages anyone who has not received the flu vaccine this year to get it now, especially before gatherings with relatives during the holidays,” the department said in a statement.

But “while undifferentiated vaccination may still provide protection, enhanced genetic, antigenic and epidemiological … surveillance is warranted to inform risk assessment and response,” scientists write in the Journal of the Assn. Medical Microbiology and Infectious Diseases Canada.

Because the vaccine isn’t a perfect match for the latest mutated flu strain, Chen Hong said getting infected patients an antiviral drug like Tamiflu may be especially important this year, even for those who have been vaccinated. This is especially true for the most vulnerable, which include the very young and the very old.

“But that means you need to diagnose earlier,” Chen Hong said. The U.S. Centers for Disease Control and Prevention says that drugs like Tamiflu work best when started one to two days after flu symptoms start.

There are now at-home flu test kits widely available for sale to people who show symptoms of the illness.

It is also worrying how the flu has developed in other countries.

Australia’s flu season has arrived early this year and has been more severe than usual. The Royal Australian College of General Practitioners said the country had seen a record flu season, with 410,000 laboratory-confirmed cases, up from the 365,000 reported last year.

“It’s not a record we want to break,” said Dr. Michael Wright, the group’s chief physician.

Hudson noted that Australia’s flu season had been “particularly tough on children” this year.

LA County health officials cautioned that Australia’s experience is not a strong predictor of what will happen locally.

“It is difficult to predict what will happen in the United States and in Los Angeles, as the severity of flu season depends on many factors including circulating pressures, pre-existing immunity, vaccination uptake and general health of the population,” said the LA County Department of Public Health.

The new pressure has also thrown a wrench in things. As the flu season came to an end in Australia, “this new strain came in, the type that caused the flu in Japan and England and other parts of Europe and Asia,” Chen Hong said.

On Friday, Japan issued a national alert following a reported surge in flu cases and hospitalizations, particularly among children and adults, along with a sharp increase in school and classroom closures. Japanese newspaper Asahi Shimbun said children between the ages of 1 and 9 and adults 80 and over were among the hardest hit groups.

According to the Central News Agency, Taiwan’s health authorities have warned of the second-highest possibility of influenza this year. There was already a spike in late September and early October — a month earlier than normal — and officials are warning that flu cases will peak in December and then peak around the Lunar New Year on Feb. 17.

Taiwanese authorities say 95% of patients with severe flu symptoms have not been vaccinated recently.

British health officials issued a “Flu Job SOS” this month as the first wave hit the nation. Public Health Minister Ashley Dalton said in a statement that flu cases are “three times higher than they were this time last year.”

In the UK, outside of epidemic years, this autumn marks the first start to the flu season since 2003-04, scientists said in the journal Eurosurveillance.

“We have to prepare for more flu cases next year,” Chen Hong said.

A major concern is declining flu vaccination rates – a trend seen in Australia and the United States.

In Australia, only 25.7% of children aged 6 months to 5 years were vaccinated against the flu in 2025, the lowest rate since 2021. Among adults age 65 and older, 60.5% were vaccinated, the lowest rate since 2020.

Australian health officials are promoting a free flu vaccine for children that does not require an injection, but is administered by nasal spray.

“We have to raise vaccination rates,” Wright said.

In the United States, officials recommend an annual flu vaccine for everyone 6 months of age or older. People age 65 and older are eligible for the high-dose prescription, and children and adults ages 2 to 49 can be vaccinated with the FluMist nasal spray, not a needle injection.

Officials this year allowed people to order FluMist to be delivered to them at home.

In addition to vaccination, other ways to protect yourself against the flu include washing your hands frequently, avoiding sick people, and wearing a mask in high-risk indoor settings, such as at the airport and on airplanes.

Healthy high-risk people, such as the elderly, may be prescribed an antiviral drug like Tamiflu if another family member has the flu, Chen Hong said.

Doctors are especially concerned about babies, toddlers and young children up to 5 years old.

“These are the kids who are the most vulnerable if they have any kind of respiratory illness. It can be really bad for them, and they can get extraordinarily sick,” Hudson said.

In the United States, only 49.2% of children had received flu shots in late April, down from 53.4% ​​who had done so at the same time last season, according to preliminary national survey results. Both figures are significantly lower than the last flu vaccination rate for eligible children during the 2019-20 season, which was 63.7%.

Among adults, 46.7% received flu shots in late April, down slightly from 47.4% at the same time last season, according to preliminary survey results, which are the most recent data.

“Prior to the COVID-19 pandemic, flu vaccination coverage was increasing slowly; declines in coverage occurred during and after the pandemic. Flu vaccination rates did not reach pre-pandemic levels,” according to the CDC.

Health experts say the denigration of vaccines by federal health officials, led by the vaccine-skeptic secretary of the US Department of Health and Human Services, Robert F. Kennedy Jr., has not helped improve immunization rates. Kennedy told The New York Times on Thursday that he himself directed the CDC to change its website to drop its position that vaccines do not cause autism.

Top health experts and former CDC officials condemned the change. “The overwhelming scientific evidence shows that vaccines do not cause autism,” Daniel Jernigan, Demeter Diskalakis and Debra Horry, all former senior CDC officials, wrote in an op-ed to MS NOW.

“The CDC has been updated to create confusion without a scientific basis. Do not trust this agency,” Daskalakis, former director of the CDC’s National Center for Immunology and Respiratory Diseases, added on social media. “This is a national shame.”

State health officials from California, Washington, Oregon and Hawaii on Friday dismissed the new claims on the CDC’s website as false, saying there is decades of “high-quality evidence that vaccines are not linked to autism.”

“More than 40 high-quality studies involving more than 5.6 million children have found no link between routine childhood vaccinations and autism,” the LA County Department of Public Health said Friday. “The increase in autism diagnoses reflects improved screening, broader diagnostic criteria and awareness, not a link to vaccines.”

Hudson said it’s important to get evidence-based information about flu vaccines.

“Vaccines save lives. Especially the flu vaccine saves lives,” Hudson said.