The biggest illness circulating right now is influenza, which accounts for about 15.8% of positive respiratory tests nationally. RSV (respiratory syncytial virus) is the second most active at 9.1%, followed by COVID-19 at 3.8%. Norovirus, the classic “stomach bug,” is also circulating at typical seasonal levels. Here’s what each of these looks like and how to tell them apart.
Flu Is the Dominant Illness This Season
Influenza A is by far the most common respiratory virus right now, making up 97% of all flu detections. Two strains are co-circulating at nearly equal levels: H1N1 and H3N2, splitting about 53% and 47% respectively. Influenza B has stayed low, peaking briefly at just 4.3% of tests in late March. Flu activity peaked in late January, when 30.4% of respiratory specimens tested positive for influenza A, but the virus continues to circulate.
This season’s flu vaccine has performed reasonably well. Preliminary CDC data shows it reduced the risk of outpatient flu illness by about 54% to 60% in children and 42% to 56% in adults, depending on the study network. That won’t prevent every infection, but it significantly lowers the chances of a severe one.
Classic flu symptoms hit fast: fever, cough, muscle aches, headache, and fatigue, often all arriving within a day. A runny or stuffy nose is common with flu, which helps distinguish it from COVID-19. Most people recover within one to two weeks, though fatigue can linger. Antiviral treatment is most effective when started within 48 hours of symptoms, particularly for people at higher risk of complications (older adults, young children, pregnant women, and those with chronic health conditions).
RSV Is Hitting Harder Than COVID-19
RSV is currently the second most active respiratory virus, with a test positivity rate of 9.1%, more than double that of COVID-19. RSV is often thought of as a baby’s illness, but it causes significant illness in older adults too. In most healthy adults, RSV looks like a bad cold: congestion, cough, low-grade fever, and general fatigue. In infants and adults over 65, it can progress to bronchiolitis or pneumonia.
There’s no widely available antiviral for RSV, so treatment focuses on managing symptoms. For most people, that means rest, fluids, and fever reducers. Vaccines are available for adults 60 and older and for pregnant women (to protect newborns), and a preventive antibody is recommended for infants entering their first RSV season.
COVID-19 Activity Is Relatively Low
COVID-19 is circulating at 3.8% test positivity, making it the least active of the three major respiratory viruses right now. Several variants are being monitored globally, including descendants of the JN.1 lineage such as KP.3.1.1 and LP.8.1, but none have triggered a major new wave.
COVID-19 symptoms still overlap heavily with flu, but a few patterns can help you tell them apart. Shortness of breath and loss of taste or smell (without nasal congestion) are more characteristic of COVID. If you’re mostly sneezing with a stuffy nose, COVID is less likely. The only reliable way to distinguish them is a test, and combination flu/COVID rapid tests are now widely available at pharmacies.
Norovirus Is Following a Normal Pattern
If what you’re dealing with is vomiting and diarrhea rather than a cough, norovirus is the likely culprit. Between August 2025 and early February 2026, 644 norovirus outbreaks were reported by participating states. That’s actually well below the 1,707 outbreaks reported during the same window last year, and falls within the normal historical range.
Norovirus spreads incredibly easily through contaminated surfaces, food, and close contact. Symptoms typically start 12 to 48 hours after exposure and include sudden onset vomiting, watery diarrhea, nausea, and stomach cramps. Most people recover within one to three days, but dehydration is the main risk, especially for young children and older adults. Alcohol-based hand sanitizers are not very effective against norovirus. Washing hands thoroughly with soap and water is the best prevention.
Walking Pneumonia in Children
One less obvious illness that’s been elevated recently is Mycoplasma pneumoniae, the bacterium behind “walking pneumonia.” The CDC has noted a sustained increase in these infections, particularly in young children. Among kids ages 2 to 4, the percentage of emergency department visits diagnosed with Mycoplasma-associated pneumonia or bronchitis rose from 1.0% to 7.2%. In children ages 5 to 17, it went from 3.6% to 7.4%. Overall test positivity across all ages climbed from 0.7% to 3.3%.
Walking pneumonia earned its name because it’s typically mild enough that people stay on their feet. Symptoms include a persistent dry cough that can last weeks, low-grade fever, fatigue, and sometimes a sore throat. It comes on more gradually than flu or COVID, often over several days. Unlike viral respiratory infections, walking pneumonia is bacterial and responds to antibiotics when treatment is needed. If your child has had a cough that won’t quit for more than a week or two, this is worth considering.
How to Tell What You Have
With so many overlapping illnesses, here’s a quick way to narrow things down based on your most prominent symptoms:
- Sudden fever, body aches, and fatigue: Most likely flu. The hallmark of influenza is how quickly it knocks you down.
- Shortness of breath or loss of taste/smell: More suggestive of COVID-19. A rapid test can confirm within minutes.
- Heavy congestion, sneezing, sore throat: Probably a common cold. These symptoms are rarely prominent in flu or COVID.
- Vomiting and diarrhea with little or no respiratory symptoms: Likely norovirus. It comes on suddenly and resolves within a few days.
- Lingering dry cough with mild fever, especially in a child: Could be walking pneumonia, particularly if it’s been going on for more than a week.
- Wheezing or difficulty breathing in an infant or older adult: RSV is a strong possibility, especially if it started as a mild cold and worsened.
Testing remains the only definitive way to distinguish flu from COVID-19, since their symptoms overlap so heavily. If you’re in a high-risk group and symptoms started within the last day or two, getting tested promptly matters because antiviral treatments for both flu and COVID work best when started early.