New strain expected to cause spike in seasonal flu cases in Stanislaus County
A new influenza strain could make for a more troublesome winter flu season in Stanislaus County.
Health agencies are saying the H3N2 subclade K variant is highly contagious, though data have not shown an increase in symptom severity.
There is no evidence yet the flu virus is making people sick in Stanislaus County. But the county most likely will be dealing with the strain before long, said Dr. Erin Gustafson, assistant county public health officer.
“The season flu has not ramped up that much,” Gustafson said. “It usually peaks in January and February.”
According to a state public health dashboard, updated Monday, test positivity for seasonal flu in San Joaquin Valley and the Bay Area rose to the “high” level, at close to 16%. Hospital admission rates for seasonal flu remained low in the same regions.
The new variant has caused large outbreaks in other countries and is spreading in most areas of the United States. It was first identified in August.
As of Dec. 19, about 90% of the H3N2 viral samples tested were subclade K, while H3N2 is the most frequently reported flu virus in the current 2025-26 season, the Centers for Disease Control and Prevention said.
There’s concern the aggressive strain is not a direct match for the flu vaccine this year. But a flu shot could help prevent severe symptoms, hospitalization or death even if it’s not a perfect match, Gustafson said.
She said it’s not too late to get the flu vaccination from a health care provider, pharmacy or a county clinic. It takes two weeks for the immunity to build up.
People who have a high risk of severe influenza, because of age or health conditions, can ask their doctor about an antiviral medication if they experience symptoms, Gustafson said.
Other precautions to keep the flu virus from spreading are handwashing, covering coughs and staying home if you’re sick. Flu symptoms often include fever, chills, sore throat, headache and fatigue.
