Flu Activity Surge in 30 States: What You Need to Know

Flu-like activity has escalated to “very high” levels in 30 states, a notable increase from the previous week, as reported by the U.S. Centers for Disease Control and Prevention (CDC). This marks the first time the CDC has classified the 2025-26 influenza season as “moderately severe”, factoring in outpatient visits, hospitalizations, and fatalities linked to the virus.

Flu Activity in California

California reported flu levels at the high end of the scale for the week ending December 27, demonstrating a significant shift from the previous weeks, where levels were categorized as moderate. The CDC estimates around 11 million illnesses, 120,000 hospitalizations, and 5,000 deaths nationwide this season, including at least nine child fatalities. A recent update highlighted a flu-related death in Sacramento County.

In California specifically, approximately 8.2% of healthcare visits are attributed to respiratory illnesses, indicating an upward trend. Currently, only four states are reported to be in “moderate” or “low” flu categories.

Regional Insights

The California Department of Public Health has flagged a rise in seasonal flu activity across all regions, with an alarming increase in test positivity among children. While hospitalizations remain low, they are expected to rise.

• In the Central California Region, positivity rates stand at a concerning 21%, categorized as “very high.”
• The Greater Sacramento and Sierra area also records a high positivity rate of nearly 16% and the highest hospitalization rate in the state at 4%.

The Emergence of Subclade K

A variant known as subclade K, a mutation of the H3N2 strain, is believed to be fueling the latest uptick in flu cases. Although it is unclear whether this variant spreads more easily or poses a greater health risk, it is particularly dangerous for vulnerable groups such as:

• Individuals aged 65 and older
• Pregnant women
• Young children
• Those with chronic health conditions, including asthma, diabetes, and heart disease.

Vaccination Recommendations

The CDC, along with many medical organizations, recommends that everyone aged 6 months and older receive a flu shot. Although the current flu vaccine may not perfectly match subclade K, health experts suggest that it could still provide partial protection. As of now, about 42% of adults and children have received the flu vaccine this year.

Dean Blumberg from UC Davis Health urges individuals to get vaccinated promptly, stating, “It’s important to get the vaccine now because it takes about two weeks to work to get that immunity, and we’ve still got several months in the flu season ahead of us.”

Common Flu Symptoms

It’s crucial to recognize flu symptoms which may include:

• Fever
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Headaches
• Fatigue
• Vomiting or diarrhea

Preventive Measures Against the Flu

To mitigate the risk of contracting the flu and other respiratory illnesses, consider the following preventive steps:

• Wash hands thoroughly and frequently.
• Cover coughs and sneezes.
• Stay home from work or school when feeling unwell.
• Use indoor masks in crowded settings.
• Improve ventilation by opening windows or holding gatherings outdoors.
• Regularly disinfect commonly used surfaces.

Stay informed about flu activity in your state through the CDC’s resources and local public health updates to manage your health and safety effectively during this flu season.