Summer is not quite over, but the respiratory virus season associated with fall and winter is already getting underway.
According to the CDC, flu season generally begins in October, reaches its highest levels from December through February and declines by spring.
This year, however, CDC surveillance data indicates that influenza activity is starting to increase earlier than usual.
Flu cases began rising during the week ending August 8. Since then, the percentage of tests returning positive has edged upward in a small but consistent trend.
Between September 5 and September 19—the most recent period for which data is available—flu test positivity doubled, climbing from 1.3 percent to 2.7 percent.
Emergency department visits linked to influenza have increased as well, although they remain low, accounting for just 0.3 percent of all ED visits.
Flu activity is still classified as “minimal” in all but four states. Even so, doctors are beginning to see signs of an early increase in hospitals and during routine office visits.
Dr Helen Chu, a professor of infectious diseases at the University of Washington, said influenza has arrived “a little bit earlier than we would’ve expected for flu.”
Doctors recommend an annual flu vaccine, which offers protection for six to eight months, to reduce the risk of infection
The graph above tracks the increase in positive flu tests. Cases began rising during the week ending August 8, followed by a modest but sustained increase in test positivity
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 where influenza levels have moved above the lowest “minimal” category. The others are Hawaii, West Virginia and South Carolina.
Health experts typically advise people to receive their flu shot by the end of October. But Chu said the earlier spread should change that advice this year: “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, commonly called the flu, is among the most widespread and contagious respiratory infections, affecting about eight percent of the US population each year.
Symptoms may include fever, coughing, sore throat, a blocked or runny nose, headaches and fatigue. In some cases, flu can cause serious complications, including pneumonia and influenza-associated encephalopathy (IAE), a severe form of brain dysfunction.
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Doctors recommend getting vaccinated against the flu every year. The vaccine provides protection for six to eight months and can reduce the likelihood of infection.
Three types of influenza viruses can cause illness in people: influenza A, B and C.
Influenza A can infect both humans and animals. Type B is generally found only in people and is typically linked to less severe infections.
Influenza C is far less common than types A and B and usually causes mild illness in humans.
The seasonal flu vaccine is reformulated each year as the virus changes. It targets influenza A and B, the strains most commonly associated with illness and severe disease.
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.
