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COVID-19 & Seasonal Flu: What are the Similarities and Differences?

October 6, 2020
Published in: COVID-19, Flu, Infectious Disease

Provider listening to a child's chest

As the flu season begins and the COVID-19 pandemic continues, the community faces the possibility of a 'twindemic'. Both are respiratory illnesses that are contagious, but because they are caused by different viruses, it is possible to have both at the same time. They share some symptoms, so telling them apart based on symptoms alone is difficult. Testing might be required to confirm a diagnosis.

COVID-19 is still very new, and researchers learn more about it every week. According to the CDC, this is the best information available to compare flu and COVID-19:

What are the symptoms?

The symptoms of both illnesses can vary from person to person. In some, the symptoms can be severe and in others who are infected, there may be no symptoms at all.

Symptoms that flu and COVID-19 have in common:

  • Fever or fever/chills
  • Cough
  • Shortness of breath (difficulty breathing)
  • Fatigue
  • Sore throat
  • Runny or stuffy nose
  • Muscle pain/body aches
  • Headache
  • Vomiting and diarrhea (more common in children than adults)

A difference:

COVID-19 symptoms include change or loss of taste or smell.

How long before symptoms appear after infection?

For both, one or more days can pass between the time a person becomes infected and symptoms begin. Generally, it takes longer for COVID-19 symptoms to start.

With flu, a person usually develops symptoms one to four days after infection. With COVID-19, symptoms typically develop five days after infection, although the range is between two days after infection to 14 days after infection.

How long is someone contagious?

It's important to know that with both flu and COVID-19, it is possible to spread the virus to someone else at least one day before having symptoms.

With seasonal flu, most people are contagious for one day before the have symptoms, and then after the symptoms appear, they are most contagious for the first three to four days. They can, however, be contagious for up to seven days. Infants and those with weak immune systems can be contagious longer than seven day.

With COVID-19, because it is so new, researchers are still studying how long infected people can spread the virus. It seems that those with COVID-19 can spread the virus for about two days before they have symptoms and are contagious for at least 10 days after symptoms appear. However, asymptomatic (those who test positive for COVID-19 but have no symptoms at all) people are also contagious for at least 10 days.

How do flu and COVID-19 spread from one person to another?

Some similarities:

Both flu's and COVID-19's main mode of transmission is spread of droplets made when an infected person coughs, sneezes, or talks. When these droplets land in or near the mouth or nose of another person, they can be inhaled and lead to infection. So those in close contact (that's the 6 foot space that's been talked about so much) for longer periods of time have an increased risk of spreading the viruses.

It is possible that someone can be infected by touching a surface or object that has the virus on it and then touching his or her own mouth, nose, or even eyes.

Remember, the virus can be spread by someone before they experience symptoms.

A Difference:

COVID -19 appears to be more contagious than the flu and appears to have had more "super-spreading events" than the flu. These are events where the COVID-19 virus spread quickly and easily to a lot of people.

Who is at high risk for complications from flu or COVID-19?

The similarities:

Both illnesses can result in severe illness, complications, and even death. Those at highest risk for both include older adults, people with underlying medical conditions, and those who are pregnant.

Some differences:

The risk of complications for healthy children is higher with flu. However, children with underlying medical conditions are at increased risk for complications with both flu and COVID-19. Also, school-age children with COVID-19 are at a higher risk for Multisystem Inflammatory Syndrome in Children (MIS-C). MIS-C is rare but severe.

What are the complications?

Complications that flu and COVID-19 have in common:

  • Pneumonia
  • Respiratory failure
  • Acute respiratory distress
  • Sepsis
  • Cardiac injury such as heart attack or stroke
  • Multiple organ failure
  • Worsening of chronic medical conditions
  • Inflammation of the heart, brain or muscle tissue
  • Secondary bacterial infections

Some differences:

An additional complication with COVID-19 is blood clots in the veins and arteries of the lungs, heart, legs or brain. Also, as previously mentioned, MIS-C is an additional complication in children.

What treatments are available?

Patients infected with either flu or COVID-19 receive supportive care to help relieve their symptoms and complications.

There are FDA-approved influenza antiviral drugs to treat flu.

There are no FDA-approved drugs for treating COVID-19. Research is in process to learn more. Remdesivir is an antiviral that is being researched for COVID-19 patients under an Emergency Use Authorization.

Is there a vaccine available?

For seasonal flu, there is an annual vaccine that is developed to protect against the three to four strains of flu that are expected each year. There is currently no vaccine for COVID-19 although several groups are working to develop one.

Source: Centers for Disease Control and Prevention