The flu circulating right now in the United States is dominated by influenza B, which accounts for nearly 73% of positive tests in clinical labs as of early March 2026. Influenza A is also circulating, with the H3N2 subtype making up about 80% of A cases. This is a notable shift from typical flu seasons, where influenza A usually leads. Here’s what you need to know about the strains going around, how they compare to other respiratory viruses, and how well this season’s treatments and vaccines are holding up.
Which Strains Are Circulating
Two types of flu are active right now: influenza A and influenza B. Influenza B has been unusually dominant this season, representing about 73% of flu-positive samples in clinical labs during the first week of March. All influenza B cases that have been lineage-tested belong to the Victoria lineage, which is the only B lineage still circulating globally.
Among influenza A cases, H3N2 is the primary subtype, responsible for roughly 80% of subtyped A samples. The remaining 20% are H1N1. H3N2 tends to cause more severe illness in older adults compared to H1N1, so this mix matters if you’re in a higher-risk group or caring for someone who is.
What About Bird Flu?
H5N1 avian influenza has been in the news, but it remains a separate situation from seasonal flu. The U.S. has recorded 71 human cases and 2 deaths, all linked to direct contact with infected animals. There is no known person-to-person spread, and the CDC rates the current public health risk as low. You cannot catch bird flu from someone who has seasonal flu, and the seasonal flu vaccine does not target H5N1.
Symptoms and How to Tell Flu From COVID
The flu hitting people right now causes the classic set of symptoms: fever, dry cough, sore throat, body aches, headache, fatigue, and a stuffy or runny nose. Some people, especially children, also experience nausea or vomiting. Symptoms come on fast, typically within one to four days of exposure, with two days being the average.
COVID-19 shares most of these symptoms, which makes the two hard to distinguish by feel alone. The biggest clinical clue is timing: flu symptoms appear quickly, while COVID symptoms can take anywhere from 2 to 14 days to develop. A loss of taste or smell still points more toward COVID than flu. If you need a definitive answer, combination rapid tests that check for both flu and COVID are widely available at pharmacies.
How Long You’re Contagious
You can spread the flu starting about one day before your symptoms appear, which is part of what makes it so hard to contain. You remain contagious for five to seven days after getting sick, though the first three days of illness are the peak window for spreading it to others. Young children and people with weakened immune systems can stay contagious even longer. If you’re trying to avoid passing it on, that first-three-day window is the most critical time to isolate.
How Well the Vaccine Is Working
This season’s flu vaccine is trivalent, meaning it targets three viruses: an H1N1 strain, an H3N2 strain, and a B/Victoria lineage strain. That lineup matches the viruses currently circulating, which is good news.
Mid-season effectiveness estimates paint a mixed but meaningful picture. For children and teens, the vaccine reduced flu-related doctor visits by 38% to 41% and hospitalizations by 41%. For adults 18 and older, it reduced outpatient visits by 22% to 34% and hospitalizations by 30%. Those numbers may sound modest, but a 30% reduction in hospitalization risk adds up significantly across millions of people. Even in seasons with lower effectiveness, vaccination consistently reduces the severity and duration of illness in people who do get infected.
Antiviral Treatment Still Works
Nearly all flu viruses circulating this season remain susceptible to the two main prescription antivirals: one that blocks the virus from releasing copies of itself from infected cells, and a newer one that stops the virus from replicating its genetic material. Both work best when started within 48 hours of symptom onset and can shorten illness by about a day while reducing the risk of complications.
One older class of antiviral drugs (adamantanes) is essentially useless against current seasonal flu. Nearly all circulating influenza A viruses are resistant to them, so they’re no longer recommended. There is also a known genetic mutation in some H1N1 viruses that can cause resistance to one of the newer antivirals, but widespread resistance has not been detected this season. If your doctor prescribes an antiviral, the available options are still effective against what’s going around.
Warning Signs That Need Immediate Attention
Most people recover from the flu within a week or two with rest and fluids. But certain symptoms signal that something more serious is developing.
In adults, get medical care right away if you experience difficulty breathing, persistent chest or abdominal pain, confusion or dizziness that won’t resolve, seizures, inability to urinate, or severe weakness. A fever or cough that improves and then comes back worse is also a red flag, as it can indicate a secondary bacterial infection like pneumonia.
In children, watch for fast or labored breathing, bluish lips or face, ribs visibly pulling in with each breath, refusal to walk due to muscle pain, or signs of dehydration like no urination for eight hours, dry mouth, or no tears when crying. Any fever in a baby younger than 12 weeks warrants immediate medical attention, regardless of how mild it seems.