Skip to content

Patient Resources

What Is “the Flu”?

What Is “the Flu”?


Update for Flu season 2023-2024

The flu is a type of germ (called a virus). It can get into the nose, throat, and lungs. Flu is also called 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 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 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) which works best in the first few days of illness.

What is the flu vaccine?

There are different types of flu viruses and they are always changing. They are grouped as Flu A and Flu B strains. Vaccines are designed to target both types in one dose.

The flu vaccine can protect you against flu germs. There are two types:

  • The flu “shot”, which is given in the arm. The flu shot is made using dead viruses so it cannot make you sick with the flu.
  • The nasal spray, which you breathe in through your nose. It is made using inactivated virus and does not give you the flu. The nasal spray can be given only to healthy non-pregnant people who are between the ages of 2 and 49 years.

If you are allergic to eggs, speak to your health care provider before getting a flu vaccine.

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 it 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 n ursing 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.
  • Women who are or will be pregnant during the flu season.

What else can I do to prevent the flu?

  • Wash your hands often and well. Use soap and water or a hand cleaner.
  • 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.
  • Wear a high-quality mask, which can help limit the spread of germs.
  • 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.

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 that can help your flu symptoms. These medicines should be started soon after the flu starts to help.
  • 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. 

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. You would need testing (with at home kits or at a testing site) to see what infection you have. 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 (N95, KN95, KF94 or 3-ply medical mask) to prevent the spread of germs to those around you.



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, and Justin Ortiz, MD
Illustration credit: OurDesigns, Inc.


Online version updated September 2023.
Am J Respir Crit Care Med Vol. 202, P21-P22, 2020
ATS Patient Education Series © 2020 American Thoracic Society



This ATS Patient Information Series fact sheet 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. 


Video Fact Sheets Audio Reading