The flu is a common respiratory illness you get from the influenza virus. Symptoms often include fever, head and body aches, coughing and a stuffy or runny nose. You’re at risk for serious complications if you have an underlying health condition or are pregnant. Getting vaccinated every year is the best way to avoid getting sick with the flu.
The flu is an illness you get from the influenza virus. It causes symptoms like head and body aches, sore throat, fever and respiratory symptoms, which can be severe. Flu is most common in winter months, when many people can get sick at once (an epidemic).
Flu season — when cases of the flu go up dramatically — in the Northern Hemisphere (which includes the U.S.) is October through May. The highest number of cases (peak) usually happen between December and February.
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The flu is one of the most common infectious diseases. Every flu season, about 20 to 40 million people in the U.S. catch the flu.
The flu and the common cold can have similar symptoms, like runny nose and cough. But cold symptoms are usually mild and flu symptoms can be severe and lead to serious complications. Different viruses cause colds and the flu.
Since they have similar symptoms, the only way to know for sure if you have the flu or COVID-19 is to get tested. They both have a risk of serious illness. But different viruses cause these infections, and providers treat them with different medications.
Certain health conditions can put you at higher risk for severe illness from the flu. This includes life-threatening complications that require hospitalization. You’re at higher risk for serious illness if you:
Non-Hispanic Black people, non-Hispanic American Indians, Alaska Native people and Hispanic or Latino people have the highest rates of severe illness from the flu compared to non-Hispanic White people and non-Hispanic Asian people.
Symptoms of the flu usually come on quickly, and can include:
You may not have all of these symptoms.
The influenza virus causes flu. Influenza A, B and C are the most common types that infect people. Influenza A and B are seasonal (most people get them in the winter) and have more severe symptoms. Influenza C doesn’t cause severe symptoms and it’s not seasonal — the number of cases stays about the same throughout the year.
Yes, the flu is contagious (it spreads from person to person). For every person infected, they spread the flu to one to two more people.
The influenza virus spreads from direct or indirect contact with someone else who’s infected. Common ways to get the flu include:
If infected, you’ll usually get symptoms of the flu one to four days after exposure (incubation period).
Your provider diagnoses the flu by listening to your symptoms and testing a sample of mucus from your nose. They’ll put a long stick with a soft tip (swab) in your nose to test for influenza. Results may take a few minutes or your provider may send the sample to a lab, where you’ll get results in a day or two.
Providers can treat the flu with antiviral medications under certain circumstances. Antivirals can reduce your risk of severe illness and shorten the amount of time you’re sick. Many people can treat the flu without prescription medications. Providers prescribe antivirals if you:
Antiviral drugs for influenza include:
Tell your provider about any health conditions you have before starting an antiviral medication.
Each antiviral medication has different side effects, but common ones include nausea and diarrhea. Inhaled medications can cause spasms that tighten and narrow your airways (bronchospasm).
Many people can manage the symptoms of flu at home with over-the-counter (OTC) medications and other therapies, including:
Not everyone should take certain OTCs, so check with your provider before you use them. It’s also a good idea to make sure certain medications are okay to use together or with supplements. Don’t give aspirin to children under the age of 16 unless their provider says it’s okay.
The best way to prevent the flu is to get the flu vaccine every year. Vaccines train your immune system to recognize infections and fight them off before you get sick. The influenza virus can change (mutate) a little bit every year, which is why you need to get vaccinated every year.
Even if you get sick with a different version of the flu than the one in the vaccine, vaccination reduces your risk of getting seriously ill. Your provider can give you the flu vaccine as a shot or as a mist they spray into your nose.
Other ways to reduce your risk of getting the flu include:
Most people are able to manage flu symptoms at home and recover within a few days to a week. Because it can cause severe illness, it’s important to keep an eye on your symptoms and get medical attention if you need it. This is especially important if you have an underlying health condition.
If you’re sick with the flu, you should avoid being around others, except to seek medical care.
Flu can last from a few days to two weeks. Symptoms like fever and body aches can come on suddenly but usually go away faster than other symptoms. A cough or runny nose can last longer.
You can be contagious with the flu from a day before your symptoms start to up to a week after. You’re most contagious for three to four days after your symptoms start. People with weakened immune systems and infants may be contagious for longer.
To avoid spreading the flu to others, you shouldn’t go back to work or school until it’s been at least 24 hours since you’ve had a fever (without taking fever-reducing medications). Your employer or school may have different requirements for returning.
The flu virus itself can cause complications or it can weaken your immune system and allow bacteria to infect different parts of your body (secondary infection). Complications and secondary infections include:
In a typical flu season in the U.S., it’s estimated that between 20,000 and 50,000 people die from the flu. Another 300,000 to 500,000 require hospitalization for serious illness.
If you think you have the flu, it’s important to get tested early on so that antiviral medications are most effective if your provider prescribes them. Contact a healthcare provider right away if:
Go to the ER or seek immediate medical attention if you have symptoms of severe illness, including:
No, gastroenteritis, commonly called “stomach flu,” isn’t caused by the influenza virus. It’s not related to the seasonal flu.
A note from Cleveland Clinic
While the flu is very common, it’s also important to remember that it can lead to life-threatening complications. Getting your flu shot is the best way to avoid getting sick and protect your loved ones and neighbors, too. If you have underlying health conditions or are pregnant, talk to your provider about reducing your risk of flu. Having the flu isn’t fun for anyone, but most people can get through with some movies and chicken soup at home.
Last reviewed by a Cleveland Clinic medical professional on 10/11/2022.
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