As of late February 2026, respiratory illness activity in the United States is moderate overall, with flu, RSV, and COVID-19 all circulating simultaneously. Norovirus is also spreading at typical seasonal levels. On top of these, measles cases have surged dramatically compared to recent years, with over 1,100 confirmed cases already reported in 2026.
Flu Is the Dominant Respiratory Virus Right Now
Influenza is driving the most emergency department visits of any respiratory virus at the moment, with activity classified as moderate and increasing. About 4.4% of outpatient visits nationally are for flu-like illness, which includes fever with a cough or sore throat. That may sound small, but it represents millions of doctor visits across the country each week.
The strain picture is shifting. Influenza A(H3N2) has been the most common strain all season, but influenza A activity is now declining while influenza B is rising in most parts of the country. All circulating influenza B viruses this season belong to the Victoria lineage. This matters because if you caught influenza A earlier in the winter, you’re not protected against B. It’s possible to get the flu twice in one season from different strains.
Flu symptoms typically hit fast: fever, body aches, fatigue, cough, and sore throat that come on over hours rather than days. If you feel fine in the morning and miserable by dinner, flu is a likely culprit.
RSV Is Hitting Young Children Hardest
RSV activity is elevated and increasing across much of the country. Emergency department visits and hospitalizations are climbing, particularly among infants and children under 5. RSV is the leading cause of infant hospitalization in the U.S., so this is the virus pediatricians are watching most closely right now.
In adults, RSV typically feels like a bad cold: runny nose, cough, mild fever. In babies and toddlers, though, it can cause wheezing, rapid breathing, and difficulty feeding. Adults over 60 with chronic health conditions are also at higher risk for serious RSV illness. For most older children and healthy adults, RSV passes on its own within a week or two.
COVID-19 Is Declining but Still Around
COVID-19 activity is decreasing nationally, with emergency department visits rated low and falling. Community viral levels remain moderate in some regions, so it hasn’t disappeared. Test positivity is sitting around 5% in surveillance data from clinical labs.
The virus has splintered into many subvariants. The XFG family of lineages currently accounts for the largest share of cases, with the parent XFG lineage at about 29% of sequenced samples and several XFG offshoots (XFG.2.5.1 at 16%, XFG.1.1 at 9%) making up additional portions. NB.1.8.1 represents about 21% of cases. None of these variants have triggered new public health alerts, but the ongoing evolution means past infection or older vaccinations provide less protection over time.
The symptom that still most reliably points to COVID over other respiratory viruses is a sudden loss of taste or smell, especially when it shows up without significant nasal congestion. Fatigue tends to be more pronounced with COVID than with a common cold, and shortness of breath can occur, which doesn’t happen with typical colds.
How to Tell These Viruses Apart
The honest answer is that you often can’t tell from symptoms alone, since flu, COVID, and RSV all cause cough, congestion, and fatigue. But some patterns help. A cold (usually caused by rhinovirus) rarely produces a fever or significant body aches and never causes loss of smell on its own. The flu tends to come on suddenly with high fever and muscle pain. COVID is more likely to cause loss of taste or smell and lingering fatigue. If your nose itches and your eyes water but you have no fever or body aches, that’s almost certainly allergies, not an infection.
Rapid home tests for COVID and flu are widely available. If you’re in a high-risk group or your symptoms are severe, testing helps guide treatment decisions since antiviral medications work best when started early.
Norovirus Is Circulating at Normal Levels
Norovirus, the most common cause of stomach bugs, is active this season. Between August 2025 and early February 2026, participating states reported 644 outbreaks to the CDC. That’s actually lower than the 1,707 outbreaks reported in the same window the previous year, and falls within the normal historical range.
Norovirus spreads incredibly easily through contaminated food, surfaces, and close contact with sick people. Symptoms are unmistakable: sudden vomiting, watery diarrhea, nausea, and stomach cramps, usually lasting one to three days. Alcohol-based hand sanitizer doesn’t kill norovirus effectively. Soap and water is your best defense.
Measles Cases Have Surged
The biggest departure from normal this year is measles. As of late February 2026, there have been 1,136 confirmed cases in the U.S., compared to just 285 for all of 2024. Ten new outbreaks have been reported in 2026, with 90% of cases linked to ongoing outbreaks. National MMR vaccination coverage among kindergarteners has dropped below the 95% threshold needed to keep measles from spreading through communities.
Measles starts with high fever, cough, runny nose, and red, watery eyes, followed a few days later by a rash that typically begins on the face and spreads downward. It’s one of the most contagious viruses known. If you or your children haven’t been vaccinated with two doses of MMR, this is the season that risk becomes very real.
Other Viruses in the Mix
Beyond the major players, surveillance labs are picking up several other circulating viruses. Seasonal coronaviruses (the older, milder relatives of COVID) are showing about 10% positivity in clinical testing. Human metapneumovirus (hMPV), which causes cold and bronchitis-like symptoms, is rising at around 4% positivity. Rhinovirus and enterovirus, the classic common cold culprits, are at about 7%. None of these are at unusual levels, but they add to the overall burden of respiratory illness.
What to Do If You Get Sick
Current CDC guidance applies to all respiratory viruses, not just COVID. If you have symptoms, stay home and away from others, including household members who aren’t sick. You can return to normal activities when both of these have been true for at least 24 hours: your symptoms are improving overall, and you haven’t had a fever without using fever-reducing medication.
After returning to normal activities, take extra precautions for the next five days. That includes wearing a well-fitting mask around others indoors, improving ventilation, keeping your distance when possible, and practicing good hand hygiene. If you develop a fever again or start feeling worse after going back to your routine, stay home and restart the process.
If you test positive for a respiratory virus but never develop symptoms, you may still be contagious. The CDC recommends five days of added precautions in that situation as well.