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Understanding the differences between influenza and COVID-19

Last Modified: October 13, 2021

flu vs covid

With flu season in full swing, you may be wondering how you can tell the difference between influenza and COVID-19 this year. And, with both viruses exhibiting similar characteristics, it may be more challenging than you think. To help differentiate between the two, we asked Andre Melendez, MD, and Rehman Ukani, MD, from Parkview Infectious Diseases, to discuss the similarities and differences of each illness plus offer up some preventative measures people can take to stay healthy this fall and winter.

What is the difference between influenza and COVID-19?

Both influenza and COVID-19 are contagious respiratory illnesses, but they are caused by different viruses. COVID-19 is more transmissible and therefore more contagious than influenza and can cause more severe disease in some people. Furthermore, the Centers for Disease Control and Prevention (CDC) estimated 28,000 flu-related deaths in 2018-2019. In contrast, COVID-19 infections attributed to 586,000 deaths between May 2020 – May 2021.

How does each virus spread?

Both influenza and COVID-19 can spread from person to person between people in close contact with one another. The viruses are expelled into the air through large and small respiratory droplets when infected individuals cough, sneeze or speak, with most of the spread occurring by inhalation. However, it may also be possible for someone to get ill by coming in contact with an infected individual or by touching a surface or object that has the virus on it, then touching their face.

What symptoms do influenza and COVID-19 share?

Both influenza and COVID-19 cause respiratory illness with symptoms that can include:

  • Fever
  • Cough
  • Runny nose
  • Sore throat
  • Muscle aches
  • Headache
  • Vomiting
  • Diarrhea

And, while a loss of taste and/or smell is also more frequent with COVID-19, both illnesses can cause a broad spectrum of diseases, ranging from asymptomatic to severe symptoms. Additionally, because we can’t distinguish between each virus based on symptoms alone, testing is needed to differentiate between the two. This will help confirm a diagnosis because many people can be infected with both at the same time.

What are the key differences between the two viruses?

Influenza and COVID-19 can each cause severe illness and complications. However, COVID-19 has been causing more serious illness even in some healthy people. This results in lengthy hospitalizations and, in some cases, death. Also, some people who have had COVID-19 can develop long-term issues and post-COVID conditions that can include fatigue, shortness of breath, an inability to exercise, difficulty concentrating, headache and prolonged loss of taste or smell.

Who’s most at risk for contracting either illness?

COVID-19 is a novel coronavirus with no preexisting immunity. Therefore, everyone is at risk of contracting it. However, those at the highest risk are older adults, people with underlying medical conditions and pregnant women. The only way to protect yourself and prevent the spread of infection is to be vaccinated.

With influenza, anyone can get sick. It is a yearly circulating virus with several strains. There is a preexisting immunity due to prior influenza infections or vaccinations in past years. This means it’s possible for someone to be exposed to influenza and only experience mild illness or forgo sickness altogether.

How long does it take for symptoms to appear after exposure or infection of each illness?

For influenza, symptoms typically start 1-4 days after infection. With COVID-19, a person usually experiences symptoms on the fifth day. However, signs and symptoms can appear anytime from 2-15 days following infection.

How long is someone contagious and able to spread each virus?

People with influenza are contagious one day before displaying any symptoms and are most contagious around days three and four. However, someone can remain contagious for up to seven days.

Individuals infected with COVID-19 can spread the virus for two days before the onset of any symptoms and will remain contagious for up to 10 days.

What are some preventative measures people can take to steer clear of either illness?

Good hand hygiene is a must, especially when in a shared space. Washing your hands is a simple way to keep yourself and others healthy while preventing the spread of either respiratory illness.

If someone is not fully vaccinated and older than two years of age, they should wear a mask when indoors in public places. If you are fully vaccinated and in an area of high transmission, you should also wear a mask indoors to maximize protection from the Delta variant and prevent spreading the viruses to others.

The most effective way to protect yourself, your family and your community are to get vaccinated against COVID-19 and influenza. There are vaccines for both viruses, including multiple FDA-licensed influenza vaccines made every year to protect against the four circulating viruses and three COVID-19 vaccines approved and authorized in the United States. Remember, vaccines are safe, effective and free.



Centers for Disease Control and Prevention