Flu Symptoms & Diagnosis
Influenza (also known as “flu”) is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and at times can lead to death. This page provides resources about flu symptoms, complications, and diagnosis.
exclamation square light iconIs it Flu or COVID-19?
Some of the symptoms of flu and COVID-19 are similar, making it hard to tell the difference between them based on symptoms alone. Diagnostic testing can help determine if you are sick with the flu or COVID-19.
Flu viruses can cause mild to severe illness. Learn common symptoms and complications.
Flu signs and symptoms usually come on suddenly. People who are sick with flu often feel some or all of these symptoms:
- Fever* or feeling feverish/chills
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Fatigue (tiredness)
- Some people may have vomiting and diarrhea, though this is more common in children than adults.
*It’s important to note that not everyone with flu will have a fever.