Flu season hits California early. Doctors worry it’ll be hard on kids

Fueled by a new viral strain, the flu is hitting California early — and doctors are warning they expect the season to be especially tough for young children.

Flu concentrations detected in wastewater have increased in the San Francisco Bay Area, and the test positivity rate is increasing in Los Angeles County and Orange County, according to state and county data. Flu hospitalizations and emergency room visits are also increasing in Los Angeles and Orange counties.

“We’re at the point where we’re starting to see a big increase in flu cases. It’s a few weeks earlier than we usually experience, but it’s very similar to what was seen in the southern hemisphere’s flu experience over their winter,” said Dr. Elizabeth Hudson, regional medical director of infectious diseases at Kaiser Permanente Southern California.

So far at Kaiser, flu cases are mostly seen in clinics, but hospitalizations usually increase after Christmas. “We expect to see the same thing this year as well,” Hudson said.

“The number of cases appears to be higher at an earlier point in the typical flu season than we have seen in years past,” she added.

Flu levels are high in San Francisco wastewater as well as in San Jose, Sunnyvale and Palo Alto wastewater, according to WastewaterSCAN and the Santa Clara County Department of Public Health.

One area of ​​concern this winter has been the rise of a relatively new subvariant of influenza, known as H3N2 influenza A subclade K, which emerged toward the end of summer. That was months after officials decided which strains this fall’s flu vaccine would target.

Subclade K “is driving an active, early flu season, with more cases occurring in some countries in the northern hemisphere,” the California Department of Public Health said.

It is still unclear whether subclade K will reduce the effectiveness of this year’s flu vaccine. Newly released data from Britain showed this season’s vaccines were between 70 and 75 percent effective against hospitalization of children from the flu, and between 30 and 40 percent in adults, consistent with expectations, the U.S. Centers for Disease Control and Prevention noted.

This suggests “that influenza vaccination remains an effective tool for preventing influenza-related hospitalizations this season,” according to the agency.

However, the expected effectiveness of the flu vaccine against symptomatic illness caused by the new subvariant remains uncertain, the World Health Organization said.

Overall, flu rates in Los Angeles County remain relatively low, but are increasing. Across California, flu hospitalizations are also low but increasing.

Nationally, severity indicators remain low, according to the CDC.

But the experience of other countries has led some experts to fear that another serious flu season could be on the cards in California.

Australia’s flu season, which is seasonally opposite California’s, arrived much earlier than usual, hit with record force and was particularly hard on the nation’s children.

Japan, Taiwan and Britain also reported early peaks in their flu seasons.

“Whether this season will be more severe or not, only time will tell,” Hudson said of California. “We know we have a mutation … that could make the flu vaccine less effective. But the vaccine still provides excellent protection against hospitalization and death, even with the mutated strain circulating.”

Based on what happened in the southern hemisphere – particularly Australia – “we expect this season to have a disproportionate impact on children under 10,” Hudson said.

Already, three influenza-associated pediatric deaths have been reported nationally this season, including two on Friday.

During the flu season that ended in September, 280 children died from the flu – the most since the 2009-10 swine flu pandemic season.

Overall, the 2024-25 season was considered the worst flu season since 2017-18 and also hit adults hard. At least 38,000 people died from the flu last season, health authorities estimate.

Only a little more than half of children who died from the flu had an underlying health condition, and 89% of those who died were unvaccinated, according to the CDC’s National Center for Immunization and Respiratory Diseases.

Among children who died from the flu last season, the most common complications before death were shock or sepsis, pneumonia, acute respiratory distress syndrome, seizures and brain damage.

Early diagnosis of the flu can help prevent the worst by giving sick people time to take antiviral medications like Tamiflu. Three in five children who died from the flu in the 2024-25 season never received antiviral medications.

Emergency warning signs of flu complications in children include difficulty breathing; bluish lips or face; the ribs tighten with each breath; chest pain; severe muscle pain, in which a child may refuse to walk; dehydration, signs of which include no urine for eight hours or no tears when crying; seizures; fevers above 104 degrees not controlled by medication; fever or cough that gets better but returns or gets worse; and any fever in newborns younger than 12 weeks.

Since the respiratory virus season officially began on October 1, the CDC estimates there have been at least 1,900 flu-related deaths, 49,000 hospitalizations and 4.6 million illnesses nationwide.

Doctors have urged everyone to get the flu vaccine — the CDC recommends it for everyone 6 months and older.

But vaccination rates are lagging. Among children aged 6 months to 17 years, about 40.8% had been vaccinated by the first week of December, according to the National Immunization Survey. During the last season before the COVID-19 pandemic, flu vaccination rates were significantly higher for this time of year, at 51.2%.

At the end of the last flu season, only 49.8% of children and adolescents had been vaccinated, the survey estimates, compared to 62.4% who were vaccinated at the end of the 2019-20 flu season.

The decline in flu vaccinations has also been observed locally. “Notably, fewer flu shots have been administered this year compared to the same time last year,” the Orange County Health Care Agency said.

It takes about two weeks for protection to build, but getting vaccinated as soon as possible before traveling or seeing friends and family “helps keep you and your loved ones safe,” the Los Angeles County Department of Public Health said in a statement to the Times.