The Flu (Influenza)

Updated for the 2024-2025 flu season

The flu (influenza) is an infection caused by a virus. It affects your respiratory tract. The respiratory tract is made up of your mouth, nose, and lungs, and the passages between them. Unlike a cold, the flu can make you very ill. The flu may lead to a serious lung infection called pneumonia. The flu can cause serious problems and even cause death.

Because of the risk of severe disease, experts strongly advise getting a flu vaccine before the start of the flu season. This protects you, your family, and others. The flu vaccine and other vaccines can be given at the same time. People at high risk for problems from the flu are likely to be at high risk for serious problems from COVID-19 and RSV. This makes it important to get a flu vaccine.

Viruses that cause influenza spread through the air in droplets when someone who has the flu coughs, sneezes, laughs, or talks.

Who is at risk for the flu?

Anyone can get the flu. But you're more likely to get the flu if you:

• Have a weak immune system

• Work in a healthcare setting where there may be flu germs

• Live or work with someone who has the flu

• Haven’t had the flu vaccine as advised

• Live in a setting with many other people. This may be an assisted living facility, a nursing home, or a shelter or group home.

How does the flu spread?

The flu is caused by a virus. The virus spreads through the air in droplets when someone who has the flu coughs, sneezes, laughs, or talks. You can get infected when you breathe in these droplets. You can get infected when you touch a surface with droplets on it and then touch your eyes, nose, or mouth. You can pick up the virus if you touch used tissues, or share utensils, drinking glasses, or a toothbrush from an infected person.

What are the symptoms of the flu?

Flu symptoms tend to start quickly. They may last a few days to a few weeks. They include:

• Fever usually higher than 100.4° F ( 38°C ) and chills

• Sore throat and headache

• Dry cough

• Runny nose

• Tiredness and weakness

• Muscle aches

• Headaches

• Vomiting and diarrhea

Who is at risk for flu complications?

For some people, the flu can be very serious. The risk for complications is higher for:

• Children under age 5

• Adults age 65 or older

• People with a chronic illness such as diabetes or heart, kidney, or lung disease

• People who live in a nursing home or long-term care facility

The risk is also higher for people with a weak immune system. This includes people who:

• Have HIV/AIDS

• Have cancer

• Had an organ transplant

• Are taking immune-suppressing medicines

How is the flu diagnosed?

Your doctor might suspect the flu based on symptoms alone. However, other infections can cause symptoms similar to the flu. The flu, RSV and COVID-19 can have similar symptoms. To confirm the diagnosis, your doctor might swab your nose or throat using a sterile cotton swab and send this to the lab for testing.

How is the flu treated?

The flu usually gets better after 7 days or so. In some cases, your healthcare provider may prescribe an antiviral medicine. It may help you get well sooner. It may reduce the risk for and severity of complications. For the medicine to help, you need to take it as soon as possible after your symptoms start. The best time is to take it within 48 hours.

If you develop pneumonia or other serious illness from the flu, you may need to stay in the hospital.

Easing flu symptoms

• Drink lots of fluids. This includes water, juice, and warm soup. A good rule is to drink enough so that you urinate your normal amount.

• Get plenty of rest.

• Ask your healthcare provider what to take for fever and pain. Don't give aspirin to children or teens. It may cause a rare but serious illness called Reye syndrome. The syndrome affects the liver and brain.

• Stay away from cigarette smoke, whether it's yours or other people’s.

• Take warm, steamy showers to help soothe your cough.

• If you have a sore throat, gargling with warm salty water, sucking on an ice cube, drinking hot water with honey and freshly squeezed lemon juice can help.

• Call your provider if your fever is 100.4° F ( 38°C ) or higher. Call if you become dizzy, lightheaded, or short of breath.

Taking steps to protect others

• Wash your hands often. Do this especially after coughing or sneezing. If you can't wash, clean your hands with a hand cleaner that has at least 60% alcohol.

• Cough or sneeze into a tissue. Then throw the tissue away and wash your hands. If you don’t have a tissue, cough and sneeze into the bend of your elbow.

• Don’t share food, utensils, drinking glasses, or a toothbrush with others.

• Stay home until at least 24 hours after fever or chills stop. Some medicines reduce fever. Check your temperature when you stop taking the medicine. 

How can the flu be prevented?

• One of the best ways to prevent the flu is to get a flu vaccine each year. Experts advise that, with rare exceptions, all people age 6 months or older get a flu vaccine every year. This includes pregnant people. The flu vaccine is advised even for people with egg allergies. Talk with your healthcare provider before getting the vaccine if:

  • You are feeling sick on the day of planned vaccination.

  • You have ever had a severe reaction from the flu vaccine

  • You have ever had Guillain-Barré Syndrome (GBS), a severe paralyzing illness

• Healthcare providers advise getting the flu vaccine each year as soon as it's available in your area. Flu virus strains change from year to year. The vaccine changes each year. This is to help protect you from flu viruses more likely to cause illness in the upcoming flu season. The vaccine comes in different forms. It's most often given as a shot into a muscle. A nasal spray is available for healthy people between ages 2 and 49 years who aren't pregnant. A needle-free form is called a jet injector. It gives the vaccine in a high-pressure stream through the skin into the muscle. This form may be an option for people ages 18 to 64. Your healthcare provider can tell you which vaccine is right for you.

• Wash your hands often. This is a proven way to help prevent the spread of infection.

• Carry a hand cleaner that has at least 60% alcohol. Use it when you can't use soap and water. Then wash your hands as soon as you can.

• Try not to touch your eyes, nose, or mouth.

• At home and work, clean phones, computer keyboards, and toys often with disinfectant wipes.

• Stay away from others who have the flu or symptoms of the flu. If around people who have the flu, wear a well-fitted mask that covers your mouth and nose.

Handwashing tips

Handwashing is one of the best ways to prevent many common infections. If you're caring for or visiting someone with the flu, wash your hands each time you enter and leave the room. Follow these steps:

• Use clean, running water and plenty of soap. Rub your hands together well.

• Clean the whole hand, including under your nails, between your fingers, and up the wrists.

• Wash for at least 20 seconds.

• Rinse, letting the water run down your fingers, not up your wrists.

• Dry your hands well. Use a paper towel to turn off the faucet and open the door.

Using alcohol-based hand sanitizer

Use a hand sanitizer with at least 60% alcohol if you don't have access to soap and water. Follow these steps:

• Apply enough of the sanitizer on your hands to cover all surfaces.

• Rub your hands together briskly. Clean the backs of your hands, the palms, between your fingers, and up the wrists.

• Rub until the gel is gone and your hands are dry. This should take about 20 seconds.

Preventing the flu in healthcare places

The flu is a special concern for people in hospitals and long-term care. To help prevent the spread of flu, many hospitals and nursing homes take these steps:

• Healthcare providers wash their hands or use an alcohol-based hand cleaner before and after treating each patient.

• People with the flu have private rooms and bathrooms. Or they may share a room with someone with the same infection.

• People who are at high risk for the flu but don't have it are encouraged to get the flu and pneumonia vaccines.

• All healthcare workers are encouraged or required to get flu shots.