Flu (Influenza): Symptoms and How Long It Lasts
Use our free symptom checker to find out if you have flu.
What it is
Flu can be deadly, but it can also be preventable. Everyone over the age of 6 months should get some form of the flu vaccine every year. Even if you have had the flu or the vaccine before. Neither gives life-long immunity. - Dr. Chandra Manuelpillai
Influenza—or the “flu”—is a common contagious disease caused by a virus. Generally, you have a fever, sore throat, muscle pain, and feel tired.
The most common time to get the flu is October to May, but peak flu season is December to February. You can get the flu more than once, even in the same year.
The best way to prevent the flu and stop its spread is the flu shot. It doesn’t always completely protect you from the flu, but if you do get it, symptoms should be milder.
Also, avoid contact with anyone who you know is sick. And maintain good hygiene, like frequent handwashing.
Most common flu symptoms
Often, people have a high fever, cough, headache, sore throat, and chills. You may also have a runny nose, muscle aches, and feel tired.
The flu may be confused with the COVID-19 virus (coronavirus). One key difference is that the flu tends to come on suddenly, while COVID-19 tends to develop and worsen over several days.
Both viruses can cause similar symptoms including fever, chills, body aches, fatigue, cough, headache, and sore throat. But the coronavirus is more likely to cause coughing and shortness of breath. (Though if the flu leads to pneumonia, it will also cause shortness of breath.) The coronavirus can also cause a loss of taste or smell.
Main symptoms of the flu
Other symptoms you may have
- Sore throat
- Stuffy nose
Gastrointestinal symptoms including nausea, vomiting, and diarrhea—more common in young children
How long does the flu last?
In most people, symptoms will peak 2 to 4 days after they start. And it can be 1 to 2 weeks before you feel completely better.
Follow up with your doctor if your symptoms get worse or you develop new symptoms.
What causes influenza?
The flu is caused by the spread of the influenza virus from an infected person. Tiny droplets that contain virus are breathed out by one person and then inhaled by another. It could happen after a cough or sneeze.
When infected, you are contagious one day before you experience any symptoms until about five days after symptoms begin.
Treatment for the flu
Discuss with your doctor your risks of developing the flu, which vaccine is best for you, and ways to prevent catching it. Also, what are the signs and symptoms you should look out for and when to go to your doctor’s office versus an urgent care or emergency department. - Dr. Manuelpillai
If you are in a high-risk group, you may be given an antiviral medication, which can reduce the symptoms by 1 to 2 days and reduce your risk of developing complications. The following treatments can ease your symptoms.
- Drink plenty of fluids.
- Rest and sleep.
- Avoid alcohol and smoking, which can lower your resistance to infections.
- You can also take over-the-counter medications to help with symptoms.
The following medications may relieve your symptoms. They will not shorten how long you have the flu.
- Acetaminophen: Decreases fever and provides pain relief.
- Ibuprofen or naproxen: Pain relief and decrease fever.
- Phenylephrine or pseudoephedrine: Clears stuffy noses.
- Dextromethorphan-guaifenesin: Reduces cough and mucus
- Prescription antiviral drugs. These can shorten how long the flu lasts, usually by 1 to 2 days. They don’t make your symptoms less severe and are usually not given to healthy people. (They can have side effects like nausea, vomiting, and diarrhea). You also must take them within the first 48 hours of when your symptoms started. These medications include Oseltamivir (Tamiflu) and Zanamivir (Relenza)
Do not give aspirin to children younger than 18 years old. It could lead to death (through a reaction called Reye’s syndrome). Always check with your pediatrician before giving any medications to a child.
What makes you more likely to have severe flu symptoms
- Age 65 or older or under 5 years old
- Being pregnant
- Have asthma, diabetes, heart disease, or are obese
- Immunocompromised (including from HIV, chemotherapy, and organ transplants)
- Live in a nursing home or long-term facilities.
Is influenza serious?
Most people recover on their own without complications. If you think you have the flu, contact your doctor, who may want to test you for the flu.
If you are at risk of severe flu symptoms, see your doctor that day or go to urgent care. They may prescribe an antiviral medication to reduce the number of days you are sick and the risk of complications.
If you have severe symptoms such as dizziness, increased heart rate, severe weakness, severe vomiting, or difficulty breathing, go to the emergency room.
Some people who receive the shot will develop mild body aches and fever from the immune response. This is not the flu, but rather your body appropriately reacting to the vaccine. - Dr. Manuelpillai
Flu prevention tips
Get your flu shot (influenza vaccine) every year. It should be available from your doctor, urgent care, clinics, pharmacies, and possibly at your workplace.
There is no life-long immunity from having the flu—you can get the flu virus even if you’ve had it before.
Because the flu virus changes from year to year, the vaccine also has different influenza strains each year. The vaccine is made based on which flu strains are predicted to be most common.