An increase in flu activity seen in SF Bay Area, experts recommend everyone aged 6 months and older to receive the flu vaccine

SAN FRANCISCO — Recent data indicates a significant surge in influenza (flu) cases this season and continues to rise nationwide with test positivity reaching high levels in the San Francisco Bay Area and very high levels in Central California. Healthcare experts have recommended that everyone aged 6 months and older receives the flu vaccines every year. 

"We are seeing increased cases of influenza A, most cases are the H3N2 Flu," said Dr. Hans Yu, Doctor of Osteopathic Medicine specializing in Internal Medicine in San Francisco. "We have not seen this strain since the 2017 flu season."

"This strain has a mutated variant called subclade-K, which seems to cause more serious disease … nicknamed 'Super Flu', " Yu said.

"In the San Francisco Bay Area, per California Department of Public Health and San Francisco Department of Public Health, we are reaching 18% of cases since Christmas, while COVID cases remain low," said Yu. "However, hospitalization due to Flu is not yet increased."

Yu advised eeryone, young and old, to get the flu vaccines. "Even though the current flu vaccine is not a good match for this 'Super Flu', those who were vaccinated had less severe disease when they caught this 'Super Flu'," Yu noted.

West Coast Health Alliance formed to provide unified recommendations on immunizations for 4 states

In response to federal actions under the Trump administration that have affected the independence of the U.S. Centers for Disease Control and Prevention (CDC), four states in the west coast, California, Oregon, Washington and Hawaii, formed the West Coast Health Alliance (WCHA) in 2025.

The Alliance was officially launched on September 3, 2025 to serve as a health-related guidance center for four western states in the nation to make their own science-based vaccine guidelines and provide unified recommendations to their residents on health issues and immunizations. The Alliance also aims to make sure vaccines are accessible to everyone.

Flu activity usually increases during the fall-winter respiratory virus season. Healthcare experts recommend people to get the flu vaccine by the end of October every year, because flu season could begin as early as November.

The WCHA issued immunization recommendations for the 2025-2026 respiratory virus season in September 2025 including advising all residents who are aged 6 months and older to get influenza vaccinations.

"Immunization is safe, effective, and the best protection available against respiratory viruses such as COVID-19, influenza, and RSV. Seasonal immunization is also a critical public health tool to reduce serious illness, community transmission, and health care systems strain," WCHA stated.

WCHA said its recommendations were based on data regarding the people most impacted by these respiratory viruses, especially the most vulnerable, the youngest and oldest individuals.

The latest data from the California Department of Public Health indicates that seasonal influenza activity has been elevated in California. This is due to the new flu strain H3N2, subclade K.

Children’s influenza positivity rate higher than adults

The data also indicates children have an influenza higher positivity rate than adults. Hospital admission rates and emergency department visits are going up. CDPH and WCHA urges vaccination, testing, and quick treatment to avoid serious illness.

Respiratory Syncytial Virus (RSV) is a common respiratory virus that usually causes mild, cold-like symptoms. Most people recover in a week or two, but RSV can be serious. Infants and older adults are more likely to develop severe RSV and need hospitalization. RSV is the leading cause of infant hospitalization in the nation.

A new vaccine came out in 2023 that protects against RSV. Vaccines for pregnant women or monoclonal antibody products are available to protect infants and young children from severe RSV. Vaccines are also available to protect adults from severe RSV.

RSV activity is also increasing across California, CDPH announced. More children and older adults are being hospitalized in recent weeks. CDPH recommends RSV immunizations for all infants younger than 8 months old, all 75 years and older, as well as all individuals between 50-74 years old with risk factors.

COVID-19 activity remains very low statewide during this season. CDPH recommends COVID vaccination for people with risk factors.

Dr. Erica Pan, who has served as Director and State Health Officer for the CDPH since February 2025, has reminded Californians to receive vaccinations for influenza, COVID and RSV in a video posted on social media channels.

"Vaccines keep you from getting sicker than you would have without a vaccine, and they may help prevent it from spreading to others. It takes about two weeks for your body to build up immunity," Pan said in the video. "If you are exposed to the virus before you've built up that immunity, you can still get sick but the vaccine helps keep the illness mild."

Pan and CDPH encouraged Californians to get vaccinated to limit spread and severity of respiratory viruses.

"Vaccines against respiratory viruses like COVID-19, influenza (flu), and respiratory syncytial virus (RSV) are the most effective and safest ways to protect themselves against severe illness this winter," CDPH said.

A flu-related death reported in San Mateo County in December 2025

San Mateo County reported an influenza-related death of a young adolescent patient in December 2025. It was the second flu-related death in San Mateo County this flu season. The patient, whose age was not disclosed, had not received this year’s flu shot and was not known if there were any underlying health conditions.

“We are deeply saddened by the loss of a young person in our community to influenza,” said Dr. Kismet Baldwin-Santana, San Mateo County health officer. “There are steps people can take to protect themselves and those around them, including getting vaccinated, staying home when sick and practicing preventative measures.”

Influenza can cause serious illness and complications, especially for people 65 years and older, people of any age with certain chronic medical conditions (such as asthma, diabetes or heart disease), pregnant women, and young children under 5 years old. It can cause mild to severe illness and at times can lead to death. Symptoms include fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, vomiting and diarrhea, San Mateo County Health noted.

To treat the flu, health care providers can prescribe antiviral medications, which can reduce the length and severity of the illness but must be administered close to the onset of symptoms.

If anyone has not gotten vaccinated yet, it's recommended to get the flu vaccine as soon as possible. "It is not too late to get vaccinated against influenza. Flu vaccination reduces the risk of serious illness, including hospitalization and death," San Mateo County Health said in a press release confirming the latest influenza- related death.

“Vaccination remains our strongest protection,” Dr. Baldwin-Santana added. “Getting the flu shot helps protect not only yourself but also your family, classmates and neighbors. We urge everyone who is eligible to get vaccinated and to take flu symptoms seriously.”

San Mateo County also has seen an increase in flu-related activity. Two of the main indicators of flu activity – emergency department visits and test positivity – are at levels consistent with previous years but are rising.

For the week of December 21-27, 2025, there were 314 flu-related emergency department visits, an increase of 98 from the previous week. Test positivity was 15.4%, an increase of 20% from the previous week.

In San Mateo County, 18 influenza-related deaths of persons under 65 were recorded in 2024-25 and 9 deaths in 2023-24.

The California Department of Public Health recommends vaccines for the following groups among all California residents:

Flu

● Children: All children 6 months or older

● Adults: All adults 18 years or older

● Pregnancy: All planning, pregnant, postpartum, and lactating

COVID-19

● Children: All children 6-23 months; All children 2-18 years with risk factors or who have never vaccinated against COVID-19; All children with close contact with others with risk factors; All children who choose protection

● Adults: All adults age 65 years or older; All adults ages 18-64 years with risk factors; All adults with close contact with others with risk factors; All adults who choose protection

● Pregnancy: All planning, pregnant, postpartum, and lactating

RSV

● Children: All children 8 months or younger; All children 8-19 months with risk factors

● Adults: All adults 75 years or older; All adults 50-74 years with risk factors

● Pregnancy: Pregnant between 32-36 weeks gestational age

The recommended vaccines by WCHA and CDPH will continue to be covered by health care insurers regulated by the state of California and can be received at local pharmacies and from health care and authorized vaccine providers.

Residents who have no health insurance may visit the websites of health departments in their counties about free immunization programs.

Homebound residents may call Aging and Disability Services at (844) 868-0938 to learn more and register for an appointment of in-home vaccination.

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Portia Li is the editor and publisher of Wind Newspaper. Prior to co-founding the Wind Newspaper in 2020, Portia was a senior and investigative reporter at the San Francisco Bureau of World Journal for over three decades. She was born and raised in Hong Kong, educated in Taiwan and the United States. She has a bachelor’s degree in Journalism from National Chengchi University of Taiwan and a master’s degree in Mass Communication from Utah State University. In 2021, Portia was a recipient of the Society of Professional Journalists (SPJ) Northern California Chapter’s Career Achievement Award in Print. She can be reached at portia@WindNewspaper.com.