Health
How to Tell Norovirus from the Flu
Health Points
- Norovirus and flu have distinct symptoms but can overlap.
- The new ‘subclade K’ H3N2 flu variant may reduce vaccine effectiveness, yet shots are still recommended.
- Norovirus mainly causes stomach issues, while flu symptoms are mostly respiratory.
New strains of flu and norovirus are making their way across the U.S., so knowing the differences in symptoms is key for staying healthy this season.
Last winter saw a record number of severe flu cases, fueling concerns the upcoming months could be just as difficult, especially with a novel H3N2 variant in circulation.
“The goal of vaccines is to reduce the severity of illness, and reduce the disease impact on our population,” says Hopkins.
Flu vaccines still offer protection against complications, though experts note this year’s shot may not perfectly match the new variant.
Adding to the challenge, norovirus activity is increasing as well, particularly in the Northeast and Midwest, with last year’s spike tied to a different emerging strain, according to recent wastewater data.
According to Dr. Stuart Ray, “there could be confusion” between norovirus and flu because both can share symptoms, though norovirus is often mislabeled as the “stomach flu.”
Norovirus Symptoms
- Nausea
- Vomiting
- Diarrhea
- Loss of appetite
Mild norovirus may only cause appetite loss and loose stools, but more severe cases can bring fever and dehydration.
Flu Symptoms
- Headache
- Fever
- Sore throat
- Nasal congestion
- Post-nasal drip
- Cough
- Muscle aches
The flu usually brings fever, body aches, and respiratory problems. Gastrointestinal symptoms are much less common with the flu, especially in adults.
“So it has some degree of frequency. But in adults, it’s actually pretty uncommon,” explains Martinello about adults experiencing nausea or vomiting with the flu.
It’s important to distinguish between these illnesses because the flu can be prevented and treated with vaccines and medications, but norovirus relies mostly on supportive care and proven prevention strategies.
Norovirus mainly leads to intense digestive troubles, frequent watery diarrhea, and vomiting that can make it tough to stay hydrated. It rarely causes respiratory issues.
By contrast, the flu is marked by congestion, cough, and other symptoms that rarely appear with norovirus. Higher fevers and body aches are also more typical with the flu.
When uncertain, experts suggest considering both your recent exposures—like an office flu outbreak or norovirus at your child’s school—and the combination of symptoms.
Pay attention to severe signs such as high fever or trouble breathing, and seek medical help if needed because flu complications like pneumonia can occur.
“Stomach flu” is not a real medical diagnosis and usually refers to norovirus or food poisoning rather than influenza itself.
Stay alert this winter by recognizing the specifics of each illness, keeping up with vaccines, and practicing careful hygiene to decrease your risk.
