Updated for the 2025-2026 influenza season

Influenza (flu) is an easily spread respiratory tract infection. It's caused by a virus. Millions of people get the flu each year. It usually starts abruptly, with fever, muscle aches, sore throat, and a cough.

The flu can make people of any age sick. Most people are sick with the flu for only a few days. But some have a much more serious illness. They may need to go to the hospital. The flu can also lead to pneumonia and death.

The flu viruses are always changing. Vaccines are developed and given each year to protect against the flu virus strains expected to cause the illness that year.

Getting a flu vaccine is more important than ever because of other illnesses such as COVID-19 and RSV. Flu vaccines are especially important for people who are at high risk from complications of the flu.

The flu is caused by a virus. Viruses are generally passed from person to person through the air when an infected person sneezes or coughs.

But the virus can also live for a short time on objects like doorknobs, pens, pencils, keyboards, phones, and cups or eating utensils. So, you can also get the flu by touching something that has been recently handled by someone infected with the virus and then touching your own mouth, nose, or eyes.

Each person may have different symptoms. The flu is a respiratory disease. But it can affect your whole body. Symptoms usually start suddenly. People usually become very sick with several, or all, of these symptoms:

• Cough, often becoming severe
• Extreme exhaustion
• Fatigue that may last for several weeks
• Headache
• High fever
• Runny or stuffy nose
• Severe aches and pains
• Sneezing at times
• Sometimes a sore throat
• Vomiting and diarrhea

Fever and body aches often last for 3 to 7 days. But cough and fatigue may last for 2 weeks or more.

The symptoms of the flu may look like other health problems. Always talk with your doctor for a diagnosis.

The flu is diagnosed based on your symptoms and lab tests. Lab tests involve a swab of your nose to confirm the diagnosis.

Treatment will depend on your symptoms, age, and general health. It will also depend on how bad the condition is.

The goal of treatment for the flu is to help prevent or reduce the severity of symptoms and any complications. Treatment may include:

• Antiviral medicines. These prescription medicines can reduce how long you'll have the flu. In some high-risk people, they can also lower the risk of complications or shorten how long they last. These medicines generally have to be started within the first 2 days of the illness. But people at the highest risk of complications or those who already have a complication may be given the medicines even after the second day of illness. These medicines do sometimes have side effects, such as nervousness, lightheadedness, or nausea, but they are generally mild.
• Other medicines. There are over-the-counter medicines for cough, congestion, and nasal discharge. You can also take medicine to relieve aches and fever. Do not give aspirin to children or teens unless your child's doctor says it is safe. Aspirin can put your child at risk for Reye syndrome, a rare but serious condition. The medicine of choice for children and teens is acetaminophen.
• Rest. Get plenty of rest.
• Staying hydrated. Drink fluids like water or broth.

Talk with your doctor for more information.

The flu can cause ear and sinus infections. Flu can make chronic conditions worse. For example, it can cause flares in people with asthma.

A serious problem is pneumonia. Other possible serious problems include infection and inflammation of the heart (myocarditis), brain (encephalitis), or muscles (myositis or rhabdomyolysis). Flu can sometimes cause a life-threatening inflammation in the body called sepsis. Sepsis is a medical emergency.

You can get a flu vaccine every year to protect yourself and others. A new flu vaccine is made each fall to protect against the flu viruses predicted to cause outbreaks during that flu season. Everyone age 6 months or older can, with rare exceptions, get a flu shot each year. The vaccine is available in different forms. The most common way to get the vaccine is by flu shot. A nasal spray is also available for healthy, nonpregnant people between ages 2 and 49.

The flu shot is safe. Experts closely watch vaccine safety. Hundreds of millions of flu vaccines have been safely given across the country for decades.

The flu shot can't give you the flu. But some of the side effects can feel like it. The most common side effects from a flu shot are:

• Feeling achy.
• Having a low-grade fever.
• Feeling soreness where the shot was given.

If you have them at all, these side effects are usually mild and last a short time.

How effective the vaccine is varies from one person to another. It can depend on things such as age and overall health.

This may also be helpful for preventing the flu:

• When possible, stay away from or limit contact with sick people.
• Wash your hands frequently with soap and water to reduce the risk of infection.
• Cover your nose and mouth when coughing or sneezing to limit the spread of the virus.

The flu causes problems that may develop into a more serious disease or become dangerous to some people. Those affected may include older adults and those with long-term (chronic) health problems. Always talk with your doctor to find out if you should get the flu shot.

Although the flu shot is safe, some people should not be vaccinated. These include:

• People who have had a severe, life-threatening reaction in the past after getting the flu shot.
• Babies younger than 6 months.

Talk with your doctor before getting a flu shot if:

• You are sick with a fever. Talk with your doctor first. You may be advised to wait until you recover to get the shot.
• Have had a severe paralyzing illness called Guillain-Barré syndrome (GBS) after getting a flu shot in the past. Some people with a history of GBS should not get a flu shot.

Most flu shots and the nasal spray flu vaccine are made using egg-based technology. The flu vaccine (either egg-based or non-egg-based) is recommended even for people with egg allergies. All vaccines should be given in settings where allergic reactions can be seen and treated quickly. Talk with your doctor about your risk. Ask which flu vaccine is right for you.

September and October are generally good times to be vaccinated. Flu season can start as early as October and most commonly peaks in the U.S. in January or February. But flu seasons are unpredictable. The flu shot takes 1 to 2 weeks to start working. Even if you can't get your vaccine by the end of October, experts still recommend getting it as long as the flu season is active.

Talk with your doctor for more information.

For most people, the flu can be treated at home without treatment from your doctor. But if you have other health problems that make you more susceptible to problems from the flu, tell your doctor when you think you have the flu. If your symptoms get worse or you have new symptoms, let your doctor know.

• The flu is an easily spread viral respiratory tract infection.
• It's caused by viruses that are generally passed from person to person through the air.
• The flu is treated with rest, plenty of fluids, and medicines to treat discomfort and fever.
• Antiviral medicines taken within the first 2 days of illness can reduce the length and severity of the disease. They may also reduce the risk of complications in those at high risk.
• Getting the flu vaccine every year is the best prevention. Flu vaccines are more important than ever because of other illnesses such as COVID-19 and RSV.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you.
• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions, especially after office hours and on weekends and holidays.