Mutated Flu Strain Fuels Early US Season, West Coast Hit Hardest

WHO:

CNN - Dr. Alex Greninger is head of the Division of Infectious Disease Diagnostics at the University of Washington’s Department of Laboratory Medicine.

CNN - Dr. Caitlin Rivers is an epidemiologist who directs the Center for Outbreak Response Innovation at the Johns Hopkins Bloomberg School of Public Health.

CNN - Walgreens reported dispensing more antiviral prescriptions and cough and cold medications than during the same period in the previous year.

CNN - The US Centers for Disease Control and Prevention provided national data on influenza-like illness.

Drudge Report - Its headline describes a mutated virus driving an early flu season, especially on the West Coast.

WHAT:

CNN - The US flu season began about 2½ months earlier than usual and initially hit West Coast states, an unusual pattern.

CNN - About 1 in 10 people tested for flu in Washington state in the article’s “last week” was positive; Greninger said flu activity was at January levels.

CNN - Walgreens said the national flu season was tracking about four weeks ahead of recent seasons.

CNN - About 2.1% of doctor visits nationally in the article’s “last week” were for influenza-like illness, still below the national baseline.

CNN - All US regions were seeing increases as the flu spread eastward from the Pacific states.

CNN - H1N1 accounted for about 98% of the samples Greninger’s laboratory was receiving.

CNN - The H1N1 virus has a G155E mutation associated with improved ability to evade immunity.

CNN - Greninger said a second wave of flu cases could follow an H1N1 peak; the severity of the overall season was uncertain.

CNN - Greninger said, “I wouldn’t be surprised to see a second flu season, like a normal flu season.”

WHERE:

CNN - The early wave began in Pacific states and was spreading eastward; Washington state was among the areas reporting high flu activity.

CNN - Greninger said the wave hitting Pacific states came from Asia.

CNN - The related H1N1 variant had already caused school and day-care closures in Japan after cases surged among children.

WHY:

CNN - The mutation emerged after strains for the season’s flu shots had been selected, so the shots may provide protection but the virus can still break through.

CNN - Flu-shot strains were selected in spring because most US flu shots are still grown in chicken eggs, which Greninger said remains common because it is inexpensive.

HOW:

CNN - Greninger said Covid-19-era tools allow viral variants to be tracked almost in real time through sequencing.

CNN - A newly approved mRNA flu shot is available for older adults; Greninger said mRNA technology could help make improved vaccines available more quickly.

CNN - Greninger advised people to get vaccinated as soon as possible, saying, “the time to get vaccinated was actually two to three weeks ago.”

(UPDATED October 22, 2026 15:05 UTC)

An unusually early flu season is spreading across the United States, starting on the West Coast and moving east. National flu activity is running about four weeks ahead of recent seasons, and Walgreens reports dispensing more antiviral prescriptions and cough and cold medicines than at this point last year. In Washington state, about one in ten people tested for flu was positive, though nationally, influenza-like illness still accounts for less than the usual baseline share of doctor visits. The virus is largely H1N1, with a mutation that may help it evade immunity. The change emerged after vaccine strains were selected, so flu shots may still protect, but infections can break through. The related variant has already fueled school and day-care closures in Japan. Experts say another wave could follow, and the season’s severity remains uncertain.