California Health Officials Report Surge in Flu Cases Amid Emergence of H3N2 Subclade K

California is witnessing a notable rise in influenza cases and hospitalizations, linked to the emergence of the H3N2 subclade K strain. The California Department of Public Health (CDPH) has reported that this new strain is contributing to increased flu activity across the state.

Dr. Elizabeth Hudson, regional physician chief of infectious diseases for Kaiser Permanente, noted that flu rates began to climb in mid-December and remain elevated. She expressed hope for a plateau in the coming weeks but acknowledged potential delays in data due to recent holidays.

The CDPH has observed high rates of positive flu cases in Central California and the Bay Area, with moderate rates around Sacramento and Southern California. Rural northern regions currently report lower flu activity.

In Los Angeles County, data indicates 162 flu-related hospitalizations and 18 intensive care admissions between late 2025 and early 2026.

Nationally, the Centers for Disease Control and Prevention (CDC) estimates at least 15 million flu infections, 180,000 hospitalizations, and 7,400 deaths since late fall. Among these, at least two pediatric deaths have been confirmed in California.

Health officials emphasize the importance of vaccination, especially for high-risk groups such as children and older adults. Despite the H3N2 subclade K strain's mutations, current vaccines are still expected to reduce severe illness and hospitalizations.

Dr. Erica Pan, state public health officer, stated that current seasonal flu vaccines remain effective at reducing severe illness and hospitalization, including against the currently circulating viruses.

Residents are encouraged to get vaccinated and seek immediate antiviral treatment if flu symptoms develop, particularly those at higher risk for complications.