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COVID-19 vs the Flu

This flu season comes with the risk of both the flu and COVID. Symptoms can be similar, including fever, sore throat, cough, body aches, and fatigue. It’s important to get tested if you’re sick and learn the differences in how to treat them.
A woman looking confused. On her left are flu viruses and on her right are covid-19 viruses.
Last updated August 29, 2022

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COVID-19 vs. the flu

As flu season approaches, Americans are at risk for both the flu (caused by the influenza virus) and COVID-19 (caused by the new coronavirus). Since they are both respiratory viruses that affect the lungs, it can be hard to know which one you have based on symptoms alone.

Understanding the differences—including who is more likely to have complications—and when to see the doctor, can help you get the care you need.

Pro Tip

Both the flu and COVID can be severe enough to be life-threatening. However, COVID appears to cause more severe illness in some people. —Dr. Benjamin Ranard

COVID and flu symptoms

COVID and the flu have many similar symptoms. They both can cause a range of illness, from no symptoms at all to severe symptoms requiring hospitalization.

Developing serious complications that require hospitalization seems to be a higher risk with COVID than with the flu. Also, in some people, there are a range of other conditions caused by COVID that doctors don’t yet fully understand, including heart, brain, kidney, and blood issues.

Similar symptoms

  • Fever and/or chills
  • Cough and/or sore throat
  • Shortness of breath due to lung infection in more serious illness
  • Runny nose or congestion
  • Muscle pain and/or body aches
  • Headaches
  • Nausea and vomiting
  • Diarrhea

Symptoms in COVID

  • Loss of taste or smell (not all COVID patients have this)

Should you get tested for COVID?

If you are having symptoms of the flu or COVID, get tested for COVID. And if you test positive, notify your close contacts to let them know they may have been exposed.

Contact your doctor or local health department if you think you have symptoms of COVID so they can determine what testing is appropriate.

There are several types of COVID tests:

  • PCR test (also called NAAT, molecular, RT-PCR, LAMP): Checks for the genetic material from the virus. Currently, PCR tests are the most accurate, although new tests of all types are under development.
  • Antigen test: Checks for specific proteins from the virus.
  • Antibody test: Checks for antibodies made from your immune system several days to weeks after infection. Antibody tests can show that you likely had COVID in the past but they aren’t good for diagnosing a new infection.

Even when not having symptoms, you may need to get tested—e.g., after a recent exposure, work or state requirements after visiting a hot-spot, monitoring by your workplace, or being a health care worker.

Causes of the flu and COVID

Pro Tip

The flu and COVID can both cause a respiratory illness, but are different diseases caused by different viruses. The flu has been around for a very long time. COVID is a new disease caused by a new virus. —Dr. Ranard

The flu and COVID are both respiratory illnesses caused by viruses. Both spread between people. Although both viruses spread similarly, COVID seems to be more contagious.

It is currently believed that most people catch these viruses after being in close contact (within 6 feet) of someone who is infected.

The viruses spread in droplets released by the infected person, generally when they talk, cough, or sneeze. These droplets spread through the air and are inhaled by a nearby person.

Both COVID and influenza can likely spread through aerosols (small particles that can stay suspended in the air). Though for influenza this is an uncommon way for it to be transmitted. Researchers are studying aerosolized viruses and how contagious they are.

You can also become infected by touching a surface that has a virus on it and then touching your mouth, nose, or eyes. Examples include shaking hands or touching a doorknob that has recently been contaminated with virus and not washing your hands afterward.

How long after exposure until symptoms develop


Symptoms generally start 1 to 4 days after you’re infected.


Symptoms start 2 to 5 days after being infected. Although symptoms may take up to 2 weeks to start in some patients.

How long can you spread the flu and COVID?

In both illnesses, it is possible to have no symptoms (often called asymptomatic) but still be contagious—i.e., spreading the virus to other people.


You are contagious starting around 1 day before symptoms. You remain infectious for about 7 days after infection but are most infectious during the first 3 to 4 days of symptoms.


COVID is contagious for a longer period of time than the flu. You are contagious about 1 to 2 days before symptoms and for about 10 days after symptoms. Though some people may be contagious for an even longer period.

How to avoid catching COVID and the flu

Dr. Rx

A flu shot helps prevent the flu. Since doctors can’t diagnose influenza and coronavirus based on symptoms alone, you want to do your best to avoid getting the flu so that you don’t then have to worry that you may actually have COVID. Influenza can also be a serious illness, so the vaccine is important for that reason alone. —Dr. Ranard

Since COVID and the flu spread in a similar way, prevention is similar. Reduce your risk of getting sick by doing what you can to not be exposed.

Your best prevention is getting vaccinated. The flu vaccine can greatly reduce your risk of getting the flu. And while it does not guarantee you won't get the flu, it usually means you’ll have a milder version if you do catch the flu.

The COVID vaccine can help protect you from catching COVID (though the Delta variant has caused some breakthrough cases). The vaccine is highly effective in preventing people from becoming seriously ill and dying from the disease.

Avoid close contact

  • When home, try to limit contact with family members who are having symptoms. This includes wearing a mask while in contact with them, and not sharing a bedroom or bathroom, if possible, with infected family members.

Wear a mask

  • With the Delta variant on the rise, the CDC recommends wearing masks indoors in public, if you are in an area of substantial or high transmission The mask should always cover both your nose and mouth.
  • Face coverings both help prevent spreading the infection and catching the infection.

Wash hands frequently for at least 20 seconds with soap and water or use hand sanitizer containing at least 60% alcohol.

  • Avoid touching your eyes, nose, and mouth until after washing hands.
  • Wash your hands after you get home, before making food and before eating, after leaving public areas, etc.
  • Washing hands after using the restroom and after sneezing/coughing/blowing your nose also helps prevent spread of disease.

Clean surfaces that are frequently touched.

  • Phones, doorknobs, keyboards, and light switches can easily become contaminated with viruses, especially when these items are shared with others.

What puts you at an increased risk of complications?


Older adults (especially those 75 and older) and people with underlying chronic diseases—like heart disease, lung disease, kidney disease, and diabetes—are at higher risk of complications from both the flu and COVID. But even those in their 40s and 50s are at greater risk than those in their 20s. The risk of complications in children may be similar with the flu and COVID, especially with the newer Delta strain of COVID, but more research is needed.


COVID is associated with a rare and serious condition in school-aged children called multisystem inflammatory syndrome.

Contact your child’s doctor if your child is showing symptoms of multisystem inflammatory syndrome—fever, vomiting, abdominal pain, diarrhea, neck pain, fatigue, rash, bloodshot eyes.

Seek emergency care if your child is confused or having difficulty breathing, chest pain, trouble staying awake or waking up, severe abdominal pain, or bluish discoloration of face or lips.

Treatment for the flu and COVID


There are several antiviral flu medications that are usually given to hospitalized patients or those who have a high risk of complications such as pneumonia from the flu. The medications are generally only somewhat effective at reducing the length of illness but may help reduce complications.

See all flu treatment options


Remdesivir is the first FDA-approved medication for treating COVID. Hospitalized patients are often treated with remdesivir (an antiviral medication) and steroids (if patients are on oxygen).

​There are also monoclonal antibody drugs for treating people who are not hospitalized. Casirivimab-imdevimab and sotrovimab work by attacking the virus and lowering the risk of symptoms worsening. They are only authorized for people who have a higher risk of severe COVID, such as those ages 65 and older, or who have an underlying health condition.

Call your doctor to discuss this option if you have COVID and are in a high-risk group.

Both illnesses are also treated with supportive care. This means that symptoms (such as fever) or complications from a lung infection (such as low oxygen levels) are treated as they occur.

See all COVID treatment options

When to call the doctor

Even if you are having mild symptoms, check in with your doctor. This is especially true for middle-aged and older adults (age 50 and older) and those with chronic medical problems. Definitely call your doctor if:

  • Symptoms haven’t started improving after more than 5 days (flu) or 7 to 10 days (COVID).
  • Symptoms are getting worse past day 3 or 4 of feeling sick.
  • Worsening of chronic medical conditions.
  • If you are concerned.

When to get emergency treatment

  • Difficulty breathing or fast breathing
  • Shortness of breath
  • New pain or pressure in the chest
  • Confusion
  • A sick person is hard to wake up
  • Not urinating
  • Severe weakness or unsteadiness
  • Bluish lips or face

This does not include every possible reason to seek emergency treatment. If you are concerned or think you are having a medical emergency, seek treatment.

The scientific understanding of COVID-19 as well as guidelines for its prevention and treatment are constantly changing. There may be new information since this article was published. It’s important to check with sources like the CDC for the most up-to-date information.

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The stories shared below are not written by Buoy employees. Buoy does not endorse any of the information in these stories. Whenever you have questions or concerns about a medical condition, you should always contact your doctor or a healthcare provider.
Dr. Ranard is a Pulmonary and Critical Care fellow at Columbia University Irving Medical Center / NewYork-Presbyterian Hospital. He received his undergraduate degree in Biological Sciences from Cornell University (2011) and his Doctor of Medicine and Masters of Science in Health Policy Research from the University of Pennsylvania Perelman School of Medicine (2016). In addition to pulmonology and c...
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