The United States is experiencing its worst flu season in three decades, with illness rates soaring to levels not seen in nearly 30 years. Data from the Centers for Disease Control and Prevention (CDC) shows that flu-like illnesses have reached a critical high, prompting urgent warnings from public health officials. This surge is driven by a newly mutated strain of influenza A (H3N2), called subclade K, which is proving highly contagious.
Unprecedented Surge in Flu Cases
As of the week ending December 27, 8.2% of outpatient visits nationwide were attributed to flu-like symptoms – fever, body aches, sore throat, and extreme fatigue. This surpasses previous peaks seen during the 2009 swine flu pandemic and last year’s season. The percentage of positive flu tests has risen by 33% in just one week, with over 11 million cases recorded so far.
Most states (45 plus D.C.) are now experiencing high to very high flu activity, leaving only Montana, South Dakota, Vermont, and West Virginia at lower transmission levels. This widespread outbreak is causing significant strain on healthcare systems and raising concerns among medical experts.
Severe Illnesses and Fatalities
Flu has already led to 120,000 hospitalizations and 5,000 deaths this season. While most individuals recover with rest and fluids, the virus can be deadly, particularly for the elderly (over 65), those with underlying respiratory or cardiovascular disease, and people with weakened immune systems. Nine children have died from flu this season, and pediatric deaths for 2024–25 totaled 289 — higher than any season since the CDC began tracking in 2004.
Experts warn that even seemingly healthy individuals can become severely ill due to rapid lung injury or secondary bacterial infections like pneumonia. Delays in seeking care or antiviral treatment can worsen outcomes.
The Role of a New Viral Mutation
The current surge is fueled by a mutation in the influenza A (H3N2) virus, subclade K, which allows it to evade existing immune defenses more effectively. Although some have labeled this a “super flu,” experts emphasize that it does not appear to cause more severe illness. Instead, the virus is simply infecting more people, leading to a proportional increase in severe cases.
Vaccine Effectiveness and Vaccination Rates
This year’s flu vaccine is considered a mismatch because manufacturers formulated it before subclade K became dominant. However, the vaccine still provides significant protection against serious illness, particularly for those who have been vaccinated.
“Most of the deaths and hospitalizations for influenza are in unvaccinated people,” says Andrew Pekosz, PhD, a virologist at Johns Hopkins Bloomberg School of Public Health.
Only about 43% of children and adults have received this year’s flu shot, contributing to higher-than-usual case numbers. Low vaccination rates hinder herd immunity, leaving vulnerable populations at greater risk.
Is It Too Late to Get Vaccinated?
No. Experts advise that it is not too late to get vaccinated, as the flu season typically extends into the spring. However, getting the shot sooner rather than later is recommended, as it takes about two weeks to become fully effective.
In addition to vaccination, public health measures such as frequent handwashing, avoiding face-touching, staying home when sick, and wearing well-fitted N95 masks in enclosed spaces can help reduce transmission. Antiviral drugs, if taken within 48 hours of symptom onset, can also help mitigate severe illness.
The current flu season is a stark reminder of the importance of vaccination and preventative measures. Despite a mismatched vaccine, it remains the best defense against serious illness and death. Public health officials urge Americans to get vaccinated as soon as possible to protect themselves and vulnerable populations.
