As of late February 2026, several respiratory illnesses are circulating across the United States at the same time. Seasonal flu is the biggest driver of illness right now, with moderate levels of emergency department visits and activity still elevated nationally. RSV is also at moderate levels and increasing, particularly among young children. COVID-19 is decreasing overall but remains elevated in some parts of the country. Norovirus, the leading cause of stomach bugs, is also active and in the middle of its peak season.
Influenza Is the Dominant Illness Right Now
Flu activity remains elevated across the country and is the respiratory virus generating the most emergency department visits. An interesting shift is happening within the flu season itself: influenza A, which typically dominates the early season, is now decreasing, while influenza B is rising nationally and in most regions. This matters because the two types can feel slightly different. Influenza B tends to hit children harder, while influenza A is more evenly spread across age groups.
Flu symptoms tend to come on fast, often within one to two days of exposure. The median incubation period for influenza A is about 1.4 days, and influenza B can hit even faster, sometimes within hours. Expect a sudden fever, body aches, chills, cough, and fatigue. Most healthy adults recover within a week, though the cough and tiredness can linger longer.
RSV Is Surging in Young Children
RSV activity is elevated in many areas, with both emergency department visits and hospitalizations increasing. The burden falls hardest on infants and children under 4 years old. For older children and adults, RSV usually feels like a bad cold with congestion, cough, and mild fever. But in babies, especially those under 6 months, it can cause difficulty breathing, wheezing, and poor feeding that requires medical attention.
RSV has a longer incubation period than the flu, averaging about 4.4 days from exposure to first symptoms. That slower onset can make it tricky to trace where a child picked it up. Symptoms in adults are often mild enough that parents and caregivers may not realize they’re carrying the virus when they pass it to a young child.
COVID-19 Is Declining but Still Circulating
COVID-19 activity is decreasing nationally, though it remains elevated in some regions. Emergency department visits for COVID are currently rated low and trending downward. The virus continues to evolve: the dominant variant family right now is XFG, which accounts for roughly 29% of sequenced cases, followed by NB.1.8.1 at about 21% and XFG.2.5.1 at 16%. No single variant has taken over completely, which is a pattern that’s become typical in recent seasons.
COVID symptoms still overlap heavily with the flu and common colds, making it hard to tell them apart without testing. COVID’s incubation period runs longer, anywhere from 2 to 14 days after exposure, compared to the flu’s 1 to 2 days. If you’re using a home rapid antigen test, timing matters. These tests are most accurate when your viral load is high, catching about 91% of high-viral-load infections. Overall sensitivity hovers around 59% to 62% in the first five days of symptoms, meaning a negative result doesn’t fully rule out infection. Testing on day 3 to 5 of symptoms, or repeating a test 48 hours after a negative result, improves your odds of getting an accurate reading.
Norovirus Is in Peak Season
Norovirus activity is solidly within its annual peak, which runs from December through March. Between August 2025 and early February 2026, participating states reported 644 norovirus outbreaks to the CDC. That’s lower than the same window last year (1,707 outbreaks) but falls within the normal range compared to the past decade of data.
Norovirus is the classic “stomach bug” that causes sudden, intense vomiting and diarrhea, often with stomach cramps and sometimes a low fever. It spreads incredibly easily through contaminated surfaces, food, and close contact. Symptoms typically start 12 to 48 hours after exposure and last one to three days. The biggest risk is dehydration, particularly for young children and older adults. Handwashing with soap and water is more effective against norovirus than hand sanitizer, since the virus lacks the outer coating that alcohol-based sanitizers target.
Walking Pneumonia Remains Elevated
Infections caused by Mycoplasma pneumoniae, the bacterium behind “walking pneumonia,” have been running above normal levels since 2024. This pathogen had nearly disappeared during the early pandemic years, then began re-emerging globally in 2023. By 2024, the percentage of pneumonia-related emergency visits linked to this bacterium had climbed significantly, peaking in late August.
The increase has been most striking in young children. Among kids ages 2 to 4, the diagnosis rate jumped from 1% to over 7%, which is unusual because this age group historically hasn’t been a major target for this infection. Children ages 5 to 17 saw a similar rise, from about 3.6% to 7.4%. Walking pneumonia earns its nickname because most people feel well enough to stay on their feet. It typically causes a persistent dry cough, low-grade fever, fatigue, and a sore throat. Symptoms develop gradually over several days, which distinguishes it from the sudden onset of the flu.
How to Tell These Illnesses Apart
With so many viruses circulating simultaneously, the symptom overlap can be frustrating. A few patterns can help you narrow things down:
- Sudden high fever with body aches: Most likely the flu. It hits hard and fast, usually within a day or two of exposure.
- Gradual onset with persistent dry cough: Could point to COVID-19 or walking pneumonia. COVID’s incubation period is longer (2 to 14 days), and walking pneumonia builds slowly over days.
- Congestion and wheezing in a young child: RSV is the top suspect, especially in kids under 4.
- Sudden vomiting and diarrhea: Almost certainly norovirus or another stomach virus, not a respiratory infection.
- Itchy eyes, clear runny nose, sneezing without fever: Likely seasonal allergies. Tree pollen season runs from February through April across most of the U.S., and it starts even earlier in southern states. Allergies don’t cause fever or body aches, which is the clearest way to distinguish them from infections.
A common cold, by comparison, develops over one to three days and mostly causes congestion and a sore throat. Most colds resolve in 3 to 10 days without fever or significant body aches.
Practical Steps to Protect Yourself
Updated vaccines for both flu and COVID-19 are available for everyone 6 months and older. This season’s flu vaccine is a trivalent formula covering H1N1, H3N2, and B/Victoria strains. The COVID-19 vaccine has been updated to better match currently circulating variants. Getting vaccinated remains the most effective way to reduce your risk of severe illness and hospitalization from either virus, even later in the season.
Beyond vaccination, the basics still work. Wash your hands with soap and water frequently, especially during norovirus season. Stay home when you’re symptomatic. If you develop respiratory symptoms and want to know what you’re dealing with, combination flu/COVID home tests are widely available. Keep in mind that rapid tests are better at confirming infection than ruling it out, so a single negative result when you feel sick doesn’t necessarily mean you’re in the clear.