Pennsylvania is currently experiencing moderate flu activity, rated at Level 7 by the CDC for the week ending February 28, 2026. The dominant strain driving illness across the state and much of the country is Influenza A H3N2, a subtype that tends to hit harder than other flu strains and has earned the informal nickname “super flu” this season.
The Dominant Strain: Influenza A H3N2
The strain responsible for most flu cases in Pennsylvania right now is a variant of Influenza A known as H3N2 subclade K. Influenza A mutates more frequently than Influenza B, spreads more easily, and historically causes more severe illness in adults. Seasons dominated by Influenza A, and H3N2 in particular, tend to produce higher hospitalization rates than seasons driven by other strains.
Influenza B is still circulating but accounts for a smaller share of cases. It generally causes milder illness in most adults, though it can still be serious for children and older adults.
Why This Season Feels Worse
Many people are reporting stronger symptoms and longer recovery times compared to recent flu seasons. H3N2 variants are associated with more intense body aches, higher fevers, and a greater risk of complications like pneumonia. The speed of spread has also been notable, with cases surging in communities quickly.
Unlike a cold, which builds gradually over a couple of days, this flu tends to come on fast. People commonly report feeling fine one day and significantly ill the next, sometimes within hours.
Symptoms to Expect
The symptom profile for H3N2 this season looks like a more aggressive version of typical flu. Common symptoms include:
- Fever and chills, often above 100.4°F
- Severe muscle and body aches that affect the whole body
- Fatigue that can linger for days or weeks, even after fever and other symptoms clear
- Cough and sore throat
- Headache or head pressure
- Nasal congestion or runny nose
The fatigue piece is worth paying attention to. Many people feel well enough to return to their routine after a week, only to find that exhaustion drags on considerably longer. That lingering fatigue is characteristic of Influenza A seasons and doesn’t necessarily mean something else is wrong.
How Well the Vaccine Matches This Strain
Preliminary CDC estimates put this season’s flu vaccine effectiveness at roughly 56%. That means vaccinated people were about half as likely to need medical care for flu compared to unvaccinated people. A 56% effectiveness rate is solidly in the middle range of what flu vaccines have delivered over the past two decades.
Even when the vaccine doesn’t prevent infection entirely, it typically reduces symptom severity and lowers the risk of hospitalization and serious complications. For H3N2 specifically, that matters, since this subtype carries a higher baseline risk of landing people in the hospital.
How H3N2 Compares to Other Flu Types
If you’ve had flu in recent years and this one feels noticeably worse, the strain is a likely explanation. Influenza A H3N2 seasons consistently produce more severe outcomes than Influenza A H1N1 or Influenza B seasons. The differences show up both in individual symptom intensity and in population-level data: more ER visits, more hospitalizations, and more pneumonia cases.
Influenza B, which is still circulating at lower levels, typically causes a milder course in healthy adults. It can still be dangerous for young children, people over 65, and anyone with chronic health conditions like asthma, diabetes, or heart disease. But for most working-age adults, the Influenza A H3N2 strain is the one responsible for the rough experiences being widely reported this season.
Recovery Timeline
Most people with H3N2 flu see their fever break within three to five days. Cough, congestion, and sore throat generally improve over the course of a week. The outlier is fatigue, which can persist for two weeks or longer in some cases, particularly in older adults or people who pushed through illness without adequate rest.
If you develop shortness of breath, chest pain, confusion, or a fever that returns after initially improving, those are signs of potential complications like pneumonia or secondary bacterial infection. Children who develop rapid breathing, bluish skin, or extreme irritability also need prompt evaluation.