This year’s influenza season in California began notably earlier than usual, with flu activity rising in late September rather than the typical early November start, according to local health officials. The early onset was first observed in Los Angeles County, where flu cases began increasing around September 28, prompting officials to encourage residents to receive their flu vaccinations promptly.
Dr. Dawn Terashita, associate director of the Los Angeles County Department of Public Health’s Acute Communicable Disease Control Program, described the timing as unusual but not entirely unexpected, citing the unpredictable nature of the flu virus due to its frequent mutations. Another atypical aspect of this season is the geographic pattern of flu emergence. Instead of starting in the southern states and then spreading northward, as has historically been the trend, this season’s activity appeared first in Western states. Dr. Elizabeth Hudson, regional chief of infectious diseases at Kaiser Permanente Southern California, noted that this shift might have contributed to some people being caught off-guard, with many either not yet vaccinated or having only recently received the vaccine, leaving insufficient time for immunity to develop.
Although flu activity has increased, hospital admissions related to influenza remain low across California at this point in the season. Positive flu test rates have been reported as high in the San Francisco Bay Area and moderate in Southern California and the Sacramento Valley. So far, the state has recorded 34 flu-related deaths this season, including the first confirmed flu death in San Francisco recently. Los Angeles County, however, has not reported any influenza-related fatalities yet. For comparison, the county logged 126 flu-related deaths during the 2025-26 season, which was considered relatively mild.
Kaiser Permanente has observed a rise in outpatient visits for flu-like symptoms, though hospitalizations have yet to increase significantly. Hudson indicated that if the current trend continues, flu hospitalizations may escalate in the coming weeks.
Health experts stress that vaccination remains the most effective defense against the flu. Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco, recommends getting vaccinated ideally before mid-October. He explained that while the standard flu shot is appropriate for most people, alternatives such as the nasal spray vaccine and higher-dose formulations are available, the latter being particularly recommended for individuals aged 65 and older. The current dominant flu strain, identified as H3N2 subclade K, is similar to last year's strain and is included in this year’s vaccine, reducing concerns about vaccine mismatch.
Looking back, Terashita recalled the 2009 H1N1 pandemic as Los Angeles County’s most severe recent flu season, marked by widespread hospitalizations and deaths. Flu activity dropped sharply during the COVID-19 pandemic due to public health measures but has since resurged as restrictions eased, with noticeable increases in cases in 2024 and 2025.
Officials continue to monitor the situation closely, emphasizing the importance of vaccination as a key strategy to limit flu severity and protect public health during the ongoing season.