San Mateo County Health is reporting the influenza (flu)-related death of an adolescent patient in December. The patient had not received this year’s flu shot, and it is not known if there were underlying health conditions. This was the second pediatric flu-related death in San Mateo County in 2025.
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.
“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.”
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.
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 and the California Department of Public Health recommend that everyone six months of age and older receive the flu vaccine every year.
Flu vaccines are available from health care providers and most pharmacies. Residents without insurance should contact County Health’s Health Coverage Unit at 650-616-2002 to ask about coverage options.
Those who are homebound and whose health care provider does not offer in-home vaccination may call Aging and Disability Services at 844-868-0938 to learn more and register for an appointment.
“Vaccination remains our strongest protection,” said Dr. Baldwin-Santana. “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.”
The Bay Area is currently seeing an increase in flu-related activity. In San Mateo County, 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 percent, an increase of 20 percent from the previous week.
In San Mateo County, 18 influenza-related deaths of persons under 65 were recorded in 2024-25 and 9 deaths were recorded in 2023-24.
Flu activity usually increases during the fall-winter respiratory virus season. Other common viruses include respiratory syncytial virus (RSV) and SARS-CoV-2 (which causes COVID-19). These viruses spread quickly. When infected, most people will have a mild illness, but some become seriously ill and can die.
Vaccines are available for all three respiratory viruses to prevent severe disease.
Preston Merchant
Communications Officer
San Mateo County Health
(650) 867-1661
press@smchealth.org