The flu is a contagious respiratory illness that anyone can get. You can spread the flu before you know you are sick, beginning one day before symptoms develop and up to five to seven days after becoming sick. Some people, especially young children and people with weakened immune systems, might be able to infect others for an even longer time.
Flu can cause mild to severe illness and sometimes becomes life-threatening. If you have asthma or other lung diseases, you are at higher risk of developing complications from the flu.
What Are the Symptoms of Influenza?
Flu symptoms often appear suddenly. People at higher risk of complications, such as those with chronic lung disease, should seek prompt medical attention. Treatment may include antiviral medicine which can reduce symptoms if started within a day or two of getting sick.
Symptoms of influenza can include:
Sudden onset of high fever
Headache, muscle aches and joint pain
Cough (usually dry)
Nasal congestion and runny nose
Stomach symptoms such as nausea, vomiting or diarrhea may occur but are more common in children than adults.
Muscle body aches and chills
Most people recover from the flu within one or two weeks, but others, especially older adults, may feel weak for a long time even after other symptoms go away.
Flu symptoms in children
Each year, millions of children get sick with the flu. Influenza can be dangerous for children, especially children younger than five who are at increased risk for developing flu complications.
Complications from flu among children younger than five can include: pneumonia, dehydration, worsening of chronic conditions like asthma, brain dysfunction, sinus problems and ear infections.
If your child under 5 is experiencing flu-like symptoms, please contact a healthcare provider right away. Flu in preschool children and infants is hard to pinpoint since its symptoms are so similar to infections caused by other viruses.
Flu Risk Factors
Some people are at increased risk for developing severe flu illness and complications if they get sick. Risk factors include:
- Adults 65 years and older
- Children younger than five years old and especially children younger than two
- Individuals that are pregnant
- Having a medical condition like:
- chronic lung diseases such as asthma, COPD, bronchiectasis, or cystic fibrosis
- heart disease and stroke
- chronic kidney disease
- diabetes or other chronic metabolic disorders
- people who are obese with a body mass index of 40 or higher
- severe anemia (including sickle cell anemia)
- people with a weakened immune system due to diseases (HIV, AIDS) or medications (chronic corticosteroids, chemotherapy) that suppress the immune system
- liver disorders
- children and adolescents who are receiving long-term aspirin therapy
When to See Your Doctor
For your yearly flu shot. Everyone 6 months and older should visit a healthcare provider every year to get a flu vaccine. The best time to go is soon after the vaccine becomes available in the fall.
If you develop flu symptoms. If you do get sick, it is important for you to call your doctor as soon as possible to receive prompt treatment with antivirals—especially if you are at high risk for complications. Antivirals can be effective in reducing the severity of flu and the duration of the disease.
For flu complications. Pneumonia can be caused by the flu virus or by bacteria that get into the lungs when the body's defense system is weakened by the flu. See a doctor if you:
- Have difficulty breathing;
- Have persistent chest or abdomen pain or pressure; or
- Are coughing up yellow, green or bloody phlegm.
- Experience worsening of your chronic medical condition(s)
Other infections that may be associated with the flu include sinusitis, bronchitis and ear infections.
If your cough won't go away. You may have a cough that lasts for weeks to months after flu symptoms go away; and it may keep you up at night. This cough has been associated with asthma-like symptoms, and can be treated with asthma medications. Consult a healthcare provider if you have this kind of cough.
Reviewed and approved by the American Lung Association Scientific and Medical Editorial Review Panel.
Page last updated: September 11, 2023