An unusual start on the West Coast
Flu is spreading months earlier than normal in parts of the United States, according to CNN. Dr. Alex Greninger, who heads the Division of Infectious Disease Diagnostics at the University of Washington's Department of Laboratory Medicine, said the season began about 2 1/2 months ahead of the typical schedule and reached West Coast states first.
That reverses the usual pattern. The flu normally arrives in the South, often in Florida, carried from the Southern Hemisphere, and then moves north as fall and winter go on. Seattle usually sees a strong peak in January, with most cases from late December through February.
This year is different. About 1 in 10 people tested for flu in Washington state last week were positive, according to the state health department. “We’re basically seeing January levels of flu in the last week,” Greninger said.
National picture
Walgreens says flu season nationally is tracking about four weeks ahead of recent seasons. The pharmacy chain is also dispensing more antiviral prescriptions and more cough and cold medicine than it did in the same period last year.
Data from the US Centers for Disease Control and Prevention show that about 2.1% of doctor visits last week were for influenza-like illness. That is still below the national baseline, meaning the virus has not taken off everywhere.
Dr. Caitlin Rivers, an epidemiologist who directs the Center for Outbreak Response Innovation at the Johns Hopkins Bloomberg School of Public Health, said the Pacific states started very early and the flu is now moving east. “All regions of the country are seeing increases at this point,” she said, in a paraphrase of her longer remarks. In the region covering Arizona, California, Hawaii and Nevada, at least 10% of flu tests came back positive last week, a sign of significant activity. Rivers said the South is catching up quickly.
A mutated H1N1 strain
Greninger said the wave on the Pacific coast came from Asia and is dominated by H1N1, the virus behind the pandemic that began in 2009. It makes up about 98% of the samples his lab is receiving now.
These H1N1 viruses have also acquired a mutation, known as G155E, that helps them evade immunity. The same version has already caused disruption in Japan, where surges among children led to school and day-care closures, and officials moved vaccination clinics earlier, CNN reported.
The mutation appeared after the strains for this year's flu shots had been chosen. The vaccines target a version of H1N1 and should still provide some protection, Greninger said, but the virus can still break through. Strains are picked in the spring because most US flu vaccine is still grown in chicken eggs, a method that persists because it is inexpensive, he added.
Vaccine timing and what comes next
Doctors often recommend a flu shot before Halloween to protect people through spring. Greninger now advises vaccination as soon as possible. He said many people, himself included, would wait until late October, but that the best time to get vaccinated was two to three weeks ago.
Rivers shares the concern about timing. “It is very early, and so I worry about vaccine timing,” she said, adding that people are not thinking about flu shots this early in the season.
Whether the early start will make the season more severe remains unclear. Greninger said a second wave is possible after H1N1 peaks. He noted that H1N1 cases will peak in 2026 and that it is unknown what may follow later in the winter or spring.
He also pointed to better tracking tools developed during the Covid-19 pandemic, which let scientists sequence viruses quickly. “We’re getting closer and closer to the weather report, right?” he said. He argued that this puts the focus on making vaccines faster. A newly approved mRNA flu shot, now available for older adults, could help, though whether it replaces egg-based vaccines is an economic question, he said.
