Summer is still winding down, but the respiratory virus season associated with fall and winter is already getting underway.
According to the CDC, flu activity usually begins to pick up in October, reaches its highest levels between December and February, and fades by spring.
This year, however, early indicators suggest influenza is arriving sooner than usual.
CDC data recorded the first noticeable increase during the week ending August 8. Flu test positivity has continued to climb gradually but consistently since then.
Over the two weeks from September 5 to September 19—the most recent period with available data—the share of positive flu tests doubled, rising from 1.3 percent to 2.7 percent.
Emergency department visits linked to influenza have also edged higher, although they remain low overall, accounting for 0.3 percent of all emergency visits.
Flu activity is still classified as “minimal” in all but four states. Even so, physicians say they are beginning to notice the virus appearing more often in hospitals and medical offices.
Dr. Helen Chu, a professor of infectious diseases at the University of Washington, said influenza appears to have arrived “a little bit earlier than we would’ve expected.”
Doctors advise getting an annual flu vaccine, which offers protection for roughly six to eight months and can reduce the risk of infection
The graph tracks the increase in positive flu tests. Activity began rising during the week ending August 8 and has continued its gradual upward trend
Chu told KUOW: “In Seattle and in Washington state, we usually see flu peak in December or January, but this year we’re seeing cases quite early.”
Washington is one of four states reporting activity above the lowest “minimal” category. The others are Hawaii, West Virginia and South Carolina.
Health experts generally urge people to receive their flu shot by the end of October. But Chu said the earlier circulation this year may justify moving up that timeline: “I would actually change that this year because of the fact that flu is circulating so early, and recommend that people actually get their flu vaccines now … it is looking like we’re seeing a very, very early surge, and if you get vaccinated now, you can be protected.”
Influenza, better known as the flu, is among the most widespread and contagious respiratory illnesses in the United States, affecting about 8 percent of the population each year.
Common symptoms include fever, coughing, sore throat, congestion, headache and fatigue. In some cases, the infection can progress to serious complications such as pneumonia or influenza-associated encephalopathy (IAE), a severe form of brain dysfunction.
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An annual flu vaccination can lower the likelihood of infection, with protection generally lasting between six and eight months.
Three influenza virus types—A, B and C—are known to cause illness in people.
Influenza A spreads among both humans and animals. Type B is typically limited to humans and is usually linked to less severe disease.
Influenza C is far less common than types A and B and generally causes milder illness.
The seasonal flu vaccine is reformulated each year as the virus changes. It targets influenza A and B, the strains most commonly associated with severe seasonal illness.
While most people recover within a week, some may develop complications such as pneumonia, which can be life-threatening and require medical treatment.
The above graph shows the rise in flu-associated outpatient visits. Flu-associated visits to the emergency department have risen – though they still remain at low levels of 0.3 percent of all ED visits
The flu shot is one of the most effective preventative measures against infection, reducing the risk of doctor visits by 34 percent and the risk of hospitalization by 30 percent, per the CDC, but it can take up to two weeks for the body to develop antibodies after receiving the vaccination.
Because of this, doctors recommend getting the shot a few weeks before an event or gathering where large numbers of people will be indoors.
Last year saw a particularly severe flu season as a ‘super flu’ surge was driven by subclade K, a highly mutated variant of the Influenza A (H3N2) virus that caused a rapid and severe spike in cases nationwide.
The strain was brand new to people’s immune systems, making them highly vulnerable and at an increased risk of severe, hospitalizing illness.
The 2025-2026 respiratory season saw at least 32 million flu cases, according to the CDC. There were about 390,000 hospitalizations and 24,000 deaths.
While symptoms were the same as other flu strains, experts warned the ‘super flu’ variant was causing more severe illness, especially in children, with signs including week-long fevers and a cough that led to trouble breathing.
To avoid the flu, health officials recommend regular handwashing and avoiding contact with people who have flu-like symptoms.
Treatment includes rest, staying hydrated, taking over the counter medication or in severe cases, prescription antivirals such as Tamiflu.