Skip to content

Patient Resources

What Is “the Flu”?

ADVERTISEMENT

Update for Flu Season 2025-2026

What is “The Flu?”

The flu is a type of germ called a virus. It can get into the nose, throat, and lungs. Flu is short for influenza (in-floo-EN-zuh). Many people who get the flu recover well, yet sometimes it can cause severe illness and even death. Getting a flu shot can not only protect you but can also help you limit the spread of the flu to other people.
 

How Do I Know If I Have the Flu?

If you have the flu, you may have:

  • Sudden fever.
  • Muscle aches.
  • Chills.
  • Sore throat.
  • Runny or stuffy nose.
  • Headache.
  • Red or itchy eyes.
  • Dry cough.

You may also feel tired or weak. Many of these symptoms can be seen with other viral infections including COVID-19. It is important to get tested if you suspect you have it. You may need treatment with medicine for the flu or COVID-19, but these medicines must be started in the first few days of illness to be effective.

What Is the Flu Vaccine?

There are different types of flu viruses and they are always changing every season. They are grouped as Flu A and Flu B strains. Vaccines are designed to target both types in one dose. The 2025-2026 season vaccines are
trivalent, which means they target two different strains of Flu A and 1 strain of Flu B.

The flu vaccine can protect you against the flu virus. The vaccine stimulates the body’s immune system to make helpful antibodies to help prevent more serious infections. There are two types of vaccines:

  • The flu “shot” is given in the arm. The flu shot is made using dead viruses so it cannot make you sick with the flu. The shot can be given to people over six months of age.
  • The nasal flu vaccine (FluMist@) is made from weakened live virus. It is squirted into the nose and may cause mild symptoms such as a runny nose or congestion for a few days. It is recommended only for healthy, non-pregnant
    people between 2 and 49 years. Beginning in fall 2025, FluMist Home@ will also be available in 34 states, allowing adults ages 18-49 to self-administer the nasal vaccine and parents to give it to children ages 2-17.

If you are allergic to eggs, speak to your health care provider before getting a flu vaccine as there are other types that can be used.

Who Should Receive a Flu Vaccine?

Flu can be serious. Flu vaccines can help prevent:

  • you from getting infected with the flu.
  • you from getting seriously ill from the flu.
  • spreading the flu to others. 

All people older than six months of age are recommended to get an annual flu shot. This includes healthy people as well as those at higher risk for serious illness, including:

  • Adults who are over 50 years old or have chronic health problems (such as lung or heart disease, diabetes, HIV/AIDS), live in a nursing home, live with or take care of babies less than six months old, or who are health care workers.
  • All children over six months old, especially those with chronic health problems or who are taking aspirin. The first season a child needs two doses of vaccine four weeks apart.
  • Women who are or will be pregnant during the flu season. Women in the third trimester (last three months of pregnancy) may want to get the vaccine earlier to help protect the baby.


Are Flu Shots Safe?

Flu shots are extremely safe. They do not contain live virus and cannot give you the flu. After a flu shot, you might have a sore arm, feel tired, or have other mild side effects as your immune system engages, but this means our immune system is working, not that you are sick. Also, note that nearly all of the supply of flu vaccine in the U.S. is produced in single-dose vials and does not contain the preservative Thimerasol, which has been talked about in the news lately. If you have any concerns about flu shot safety or effectiveness, talk about those concerns with your healthcare provider, who is your partner in health.

What Else Can I Do to Prevent the Flu?

  • Wash your hands often and well. Use soap and water or a hand sanitizer.
  • Avoid being near people who are sick.
  • Keep a physical distance of at least six feet to limit spread from someone who is coughing or sneezing.
  • In situations where exposure risk could be high during flu season (like crowded indoor spaces), wear a high-quality mask (N95, KN95, KF94 or 3-ply medical mask), which can help limit the spread of the virus.
  • Keep good control of medical problems, such as asthma.
  • Do not smoke or vape and avoid being around any tobacco smoke or vapors.
  • Cover your nose and mouth with a tissue when you sneeze or cough and throw away the tissue afterward and wash your hands.

What Should I Do if I Get Sick with the Flu?

  • Treat signs of flu with medicines that relieve pain and fever (such as acetaminophen or ibuprofen). Never give a child aspirin without first speaking to your doctor.
  • Ask your doctor about prescription medicines specific for the flu that can help fight against the flu and help with your flu symptoms. These medicines should be started soon after the flu is diagnosed with the first signs of infection.
  • Rest as much as possible.
  • Drink plenty of liquids.
  • Cover your nose and mouth with a tissue when you sneeze or cough and throw away the tissue afterward. Wash your hands often and well.
  • Stay home from work or school to keep from giving others the flu.

Can I Get a Flu Vaccine at the Same Time as the COVID-19 Vaccine?

Yes, the flu vaccine can be given at the same time as the COVID-19 vaccine. Remember to get your flu vaccine before or early in the flu season, as the shot takes a few weeks to start working. It is important to get both vaccines to protect yourself and those around you from these serious illnesses.

Where Can I Get the Flu Vaccine?
The flu vaccine is available in many places including pharmacies and medical clinics. Sometimes it is offered in health fairs as well. 

You don’t usually need a prescription to get a flu vaccine (though some places will not give it to young children and have to go to a clinic).

If you are unsure where to get it, you can check with your primary care provider or lung specialist. Some people can use the nasal vaccine that will be available as a home administration.

How Can I Tell if I Have the Flu or COVID-19 Infection?

Flu viruses and the SARS-CoV-2 virus that causes COVID-19 spread easily and are both likely to be around together this flu season. They all can cause a range of infection from mild to severe life-threatening illness. Symptoms of flu and COVID-19 are very similar. It is possible to have infection from more than one virus at the same time.

You need testing (with at-home kits or at a testing site) to see what infection you have. Home-test kits that test for both flu and COVID-19 are now available. People can spread these viruses before they have symptoms and, in some cases, even without symptoms.

Be careful to limit your exposure to flu and other viruses. If you are sick, call your health care provider before going to a clinic or ED to plan your visit. If you are sick and need to go out, wear a high-quality mask to prevent the spread of germs to those around you.

Resources:

American Thoracic Society

  • COVID-19 and Lung Health
  • How Vaccines Work to Prevent Infections

Centers for Disease Control (CDC)

This information is a public service of the American Thoracic Society. 
The content is for educational purposes only. It should not be used as a substitute for the medical advice of one’s health care provider.

Author: Marianna Sockrider, MD, DrPH
Reviewers: Kathleen Hiltz, MD; Vidya Krishnan, MD; Justin Ortiz, MD; W. Graham Carlos, MD; Charles Dela Cruz, MD; Jane E. Gross, MD; Shazia Jamil, MD; and Susan Pasnick, MD.
 

Online version updated September 2025 
Am J Respir Crit Care Med Vol. 202, P21-P22, 2020
ATS Patient Education Series © 2024 American Thoracic Society

 

 

CMSS SSAAI

This ATS Patient Information Series fact sheet update is supported by the Centers for Disease Control and Prevention (CDC) of the U.S. Department of Health and Human Services (HHS) as part of a financial assistance award to the Council of Medical Specialty Societies (CMSS) with 100 percent funded by CDC/HHS. The contents are those of the authors and do not necessarily represent the official views of nor endorsement, by CDC/HHS or the U.S. Government.