COVID-19 vs the Flu

Learn the difference between these two respiratory viruses and when to get medical care.

COVID-19 vs the flu

Pro Tip

Both the flu and COVID-19 can be severe enough to be life-threatening. However, COVID-19 appears to cause higher rates of severe illness. This may be at least partially because it is a new disease that people haven’t been exposed to before. —Dr. Benjamin Ranard

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.

COVID-19 and flu symptoms

COVID-19 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 higher with COVID-19 than with the flu. Also, in some people, there are a range of other conditions caused by COVID-19 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-19

  • Loss of taste or smell (not all COVID-19 patients have this)

Should you get tested for COVID-19?

If you are having symptoms of the flu or COVID-19, get tested for COVID-19. 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-19 so they can determine what testing is appropriate.

There are several types of COVID-19 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-19 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-19

Pro Tip

The flu and COVID-19 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-19 is a new disease caused by a new virus. —Dr. Ranard

The flu and COVID-19 are both respiratory illnesses caused by viruses. Both spread between people. Although both viruses spread similarly, COVID-19 seems to be more contagious.

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

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-19 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

Flu

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

COVID-19

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-19?

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.

Flu

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-19

COVID-19 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-19 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-19. Influenza can also be a serious illness, so the vaccine is important for that reason alone. —Dr. Ranard

Since COVID-19 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.

At least for now, one difference is that there is a vaccine for the flu. The flu vaccine is your greatest protection against 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.

Avoid close contact

  • Try to stay at least 6 feet away from other people when outside your home.
  • 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 when outside—it 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. You don’t want to touch your face with your hands when your hands have been exposed to virus.
  • Washing hands is a must right 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?

Similarities

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-19. But even those in their 40s and 50s are at greater risk than those in their 20s.

Differences

Flu seems to have higher risk of severe disease in young children. Though COVID-19 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-19

Flu

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.

COVID-19

Remdesivir is the first FDA-approved medication for treating COVID-19. Hospitalized patients are often treated with Remdesivir (an antiviral medication) and steroids (if patients are on oxygen).

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.

When to call the doctor

Even if you are having mild symptoms, check in with your doctor. This is especially true for middle-age 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-19).
  • 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.

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