Flu in California: Flu Season 2026 to 2027
2.5% of outpatient visits in California were for influenza-like illness in the week ending Sep 12, 2026. Flu activity in California usually peaks in early January.
Flu in California this season against the median
2.5% of outpatient visits in California were for influenza-like illness in the week ending Sep 12, 2026, between seasons and under the 2.7% level that marks the start of flu season there. Influenza-like illness, in the CDC’s outpatient network, means a visit for fever with a cough or sore throat. Weekly reporting for the 2026 to 2027 season starts with the week ending Oct 10, 2026; until then the chart shows the 2025 to 2026 season against the median.
Between seasons. Season threshold: 2.7%.
Source: CDC ILINet, via the Delphi Epidata API. Median: each week’s middle value across 10 seasons since 2015 to 2016, leaving out 2020 to 2021. Season threshold: the median of MMWR weeks 40 to 43 plus one percentage point, 2.7%. Compiled 2026-09-22.
Flu hospital admissions in California
Hospitals in California reported 213 new laboratory confirmed flu admissions in the week ending Sep 12, 2026. Last season's busiest week, ending Feb 14, 2026, had 2,151. Admissions are laboratory confirmed, so they count flu itself, and they rise a week or two behind visits.
Source: CDC NHSN Weekly Hospital Respiratory Data, field totalconfflunewadm. Compiled 2026-09-22 and refreshed in the browser each visit.
When flu peaks in California
The median peak week in California falls in early January, against late January nationally. Across 10 seasons since 2015 to 2016, the earliest peak came in late November (2022 to 2023) and the latest in mid February (2018 to 2019). The 2025 to 2026 season peaked in the week ending Jan 3, 2026 at 6.3% of visits.
The biggest flu season in California since 2015
The 2024 to 2025 season holds the highest weekly share in California’s ILINet record since 2015 to 2016: 9.3% of outpatient visits in the week ending Dec 28, 2024, where the median curve tops out at 5.3%.
2020 to 2021 is left out: “There was no discernible peak in flu activity during the 2020-2021 season due to the uncharacteristically low level of influenza virus circulation that season.” CDC, Flu Season.
What the CDC says about flu shots and spread
“For most people who need only one dose of influenza vaccine for the season, September and October are generally good times to be vaccinated against influenza. Ideally, everyone should be vaccinated by the end of October.”CDC, Who Needs a Flu Vaccine, Sept. 18, 2025, quoted exactly.
“Everyone 6 months and older should get an annual flu vaccine, ideally by the end of October but people should continue to get vaccinated as long as flu viruses pose a threat to their community.”CDC, Preventing Seasonal Flu, Sept. 1, 2026, quoted exactly.
“Most experts think that influenza viruses spread mainly by droplets made when people with flu cough, sneeze, or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.”CDC, How Flu Spreads, Sept. 17, 2024, quoted exactly.
“People with flu are most contagious during the first three days of their illness.”CDC, How Flu Spreads, Sept. 17, 2024, quoted exactly.
Questions people ask about flu in California
ILINet and NHSN figures compiled 2026-09-22 from the sources linked above and refreshed in the browser each visit. CDC quotes copied exactly from the pages linked.