Flu vs. COVID-19: What you need to know

By Jenilee Matz, MPH Sep 12, 2021 • 5 min

Seasonal influenza (the flu) and COVID-19 are viral respiratory infections that can cause mild to severe illness.

Both illnesses can cause complications that may require hospitalization, especially in older adults and people of any age with certain underlying health conditions. In some cases, the complications can even be fatal. While the illnesses share some characteristics, they are unique viruses with important differences. Here's what you need to know about the flu and COVID-19.

How the illnesses spread

Flu viruses and the virus that causes COVID-19 are both contagious, but COVID-19 seems to spread more easily than the flu. The viruses are mainly spread between people through large and tiny respiratory droplets when an infected person coughs, sneezes or talks. These droplets can land in the noses and mouths of people who are nearby and possibly be inhaled into the lungs. Spread is more likely when people are in close contact with one another (within about 6 feet). Less often, people may become infected when they touch a surface that contains the virus and then touch their mouths, noses or possibly eyes. Note that people who are infected with the flu or COVID-19 can be contagious for days before they develop symptoms. In general, people with COVID-19 may take longer to show symptoms, and they may be contagious for a longer period of time compared to those with the flu.

Symptoms to watch for

The flu and COVID-19 can each cause a variety of symptoms ranging from mild to severe, and in some cases, there are no symptoms (asymptomatic). The viruses cause many of the same symptoms, and it isn’t always possible to tell which virus you have based on symptoms alone. The only way to confirm which virus is causing your symptoms is to get tested.

Symptoms of the flu tend to develop within one to four days of exposure to the virus. With COVID-19, symptoms appear within two to 14 days after the virus enters your body, typically around five days. Symptoms of both illnesses include:

  • Fever
  • Chills
  • Headache
  • Body aches and muscle pains
  • Fatigue
  • Shortness of breath or trouble breathing
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Vomiting or diarrhea
  • Loss of or a change in taste or smell (more common with COVID-19)

The following are emergency signs of illness. If you have any of these symptoms or other symptoms that are concerning to you, seek medical help right away:

Flu emergency warning signs COVID-19 emergency warning signs
  • Trouble breathing or shortness of breath
  • Constant pain or pressure in the chest or abdomen
  • Persistent dizziness, confusion or inability to wake up
  • Seizures
  • Not urinating
  • Severe muscle pain
  • Severe weakness or unsteadiness
  • Fever or cough that improves but then comes back or gets worse
  • Worsening of chronic health conditions
  • Trouble breathing
  • Constant pain or pressure in the chest
  • New confusion
  • Inability to wake up or stay awake
  • Pale, gray or bluish lips, skin or nail beds

In children, emergency warning signs of the flu can also include fast breathing, bluish lips or face, ribs pulling in with each breath, chest pain, not urinating for eight or more hours, dry mouth, no tears when crying, loss of alertness or a fever over 104°F. In children younger than 12 weeks, any fever is an emergency.

People at risk for severe illness

Anyone can become infected with the flu or COVID-19 if they are exposed to the viruses that cause these illnesses. In many cases, infections are mild, and people are able to recover on their own. However, both COVID-19 and the flu can cause severe illness and complications. COVID-19 seems to cause more serious illness, though, and it can lead to hospitalization and even be fatal in people without risk factors. Note that getting the flu shot and the COVID-19 vaccine can reduce your risk for severe illness.

Certain people have a higher risk of severe illness and complications, including:

Higher risk of flu complications Higher risk of severe COVID-19 illness
  • People 65 years and older
  • Children 5 years and younger, especially those 2 years and younger
  • Women who are pregnant
  • People with chronic medical conditions, such as diabetesheart disease and asthma
  • People with weakened immune systems, including those with human immunodeficiency virus (HIV), acquired immunodeficiency syndrome (AIDS) or an organ transplant
  • People with health or social inequities (racial and ethnic minorities)
  • People in their 50s and older—the risk goes up with age
  • Women who are pregnant or who were pregnant within the past 6 weeks
  • People with underlying medical conditions, such as chronic lung diseases, moderate to severe asthma, cancer, heart issues, stroke, diabetes, liver disease, chronic kidney disease, Down syndrome, certain blood disorders, dementia and other conditions that affect the brain, nerves and spinal cord
  • People who are overweight or have obesity
  • People who smoke or used to smoke
  • People with substance abuse disorders
  • People with weakened immune systems, including those who have received cancer treatment or an organ transplant or who have HIV or AIDS
  • People with health or racial inequities (racial and ethnic minorities)

Which virus do I have?

Since both infections share many of the same symptoms, it may not be possible to know which illness you have without seeing your healthcare provider or getting tested. If you have symptoms of the flu or COVID-19, contact your provider, especially if you are at high risk for severe infection. They may examine or test you for the flu or COVID-19. (Walgreens is offering flu testing and COVID-19 testing at select locations.)


Most people who become infected with the flu or COVID-19 recover on their own. For mild cases, the goal of treatment is to ease symptoms. Getting enough sleep, drinking plenty of fluids and using over-the-counter medicines can temporarily relieve symptoms.

If you have the flu, your healthcare provider may prescribe antiviral medications. When treatment is started promptly after you begin to feel sick, these medications can lessen symptoms and shorten the length of your illness by about one to two days. Antiviral medicines may also reduce the risk of flu-related complications.

At this time, remdesivir (Veklury) is the only medication approved by the U.S. Food and Drug Administration (FDA) to treat COVID-19. The FDA has also issued emergency use authorization (EUC) for other COVID-19 treatments. EUC allows healthcare providers to treat COVID-19 using investigational therapies that aren’t yet FDA-approved or ones that are approved for other uses.


According to the Centers for Disease Control and Prevention (CDC), getting the flu vaccine and the COVID-19 vaccine is the best way to protect yourself from both illnesses.

  • Flu vaccination can prevent flu-related illnesses, healthcare provider visits and hospitalizations, and it can even be lifesaving in children. Everyone age 6 months and older should get a flu shot each year.
  • The COVID-19 vaccines are highly effective in preventing severe illness, hospitalization and death due to the illness. You should receive a COVID-19 vaccine if the CDC recommends it for your age group.

Note that the CDC states that you can receive a flu shot and COVID-19 vaccine at the same time. In fact, you can get the COVID-19 vaccine with other vaccines on the same day.

There are also everyday actions you can take to reduce your risk of getting sick with COVID-19 or the flu:

  • Wash your hands often. Wash your hands with soap and water for at least 20 seconds after coughing, sneezing, blowing your nose and being in public settings. When soap and water aren't available, use a hand sanitizer that contains at least 60% alcohol.
  • Do not touch your mouth, nose or eyes with unwashed hands.
  • Keep your distance from others. Stay at least 6 feet away from other people, especially those who are sick. If someone in your home is ill, try to keep your distance from them, too.

If you have either illness, it's important to try to avoid spreading it to others. Stay home, except to get medical care, when you're sick. Since you may be able to pass illness to others before you know you're sick, the CDC recommends wearing face masks that cover your nose and mouth in public settings to keep from spreading COVID-19 to others, especially if you’re in areas with substantial community spread or if you aren’t fully vaccinated.

Clinically reviewed and updated September 2021.

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