Flu vs COVID-19

Sep 17, 2020 | Clinical Insight

Coexistence of the two Viruses

It is not yet known how the two respiratory illnesses will coexist.  In the US, influenza season usually begins in October and peaks between December and February.  The seasonality of COVID-10 remains to be determined. Coinfection MAY lead to worse outcomes; therefore, vaccinating against influenza and other vaccine-preventable infections will be a high priority for the upcoming year. 


  1. Similarities and Differences between COVID-19 and influenza. CDC website. Accessed August 24, 2020.
  2. Co-circulation of Influenza Viruses and SARS-CoV-2. CDC website. Accessed August 24, 2020.
  3. The flu season. CDC website. Accessed August 26, 2020.

*Note: information included in this document is current as of 8/24/20 and may evolve as COVID-19 is a rapidly evolving situation.

Influenza (Flu) and SARS-CoV-2 (COVID-19) 

Because it is not yet known how Influenza and COVID-19 will coexist, it is important to know how they are similar and how they differ.  This article will walk you through the signs, spread, complications, and treatments of influenza and COVID-19.

Both are Virial Respiratory Illness

Both the flu and COVID-19 are contagious respiratory illnesses that are caused by viruses. They can both spread from person-to-person, between people who are in close contact (within about 6 feet of one another).  They are both spread mainly by droplets.  Droplets that contain the virus can be released when people cough, sneeze, or talk and then land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.  They may also spread via physical human contact (i.e. shaking hands) or touching a surface that has virus on it and then touching one’s own mouth, nose, or eyes.

Symptoms that Influenza and COVID-19 have in Common

Both may present with: fever, chills, cough, myalgias, headaches, sore throat, shortness of breath, fatigue, runny or stuffy nose.  Some may have vomiting and diarrhea, though these symptoms are more common in children.

The degree of symptoms for both can vary from none at all (asymptomatic) to severe. One or more days can pass between a person becoming infected and when they start to experience illness symptoms.

Shared Complications of the Viruses

Influenza and COVID-19 both can result in the following complications:

  • Pneumonia
  • Respiratory failure
  • Acute respiratory distress syndrome
  • Sepsis
  • Cardiac injuries (i.e. MI, stroke)
  • Multiple-organ failure
  • Worsening of chronic medical conditions
  • Secondary bacterial infections

Immunocompromised patients such as those with underlying lung disease and older adults are at a high risk of developing severe manifestations of both infections.

The Importance of Testing

Because of their overlapping symptoms, it can be hard to tell the difference between the two illnesses based on symptoms alone.  Testing will therefore play a very important role in helping to confirm a diagnosis.  The CDC has developed a test that can check for A and B type seasonal flu viruses and SARS CoV-2.  Clinicians should not wait for the results of influenza testing, SARS-CoV-2 testing, or multiplex molecular assays that detect influenza A or B viruses to initiate empiric antiviral treatment for influenza in the following priority groups:  

  1. Hospitalized patients with respiratory illness
  2. Outpatients with severe, complicated, or progressive respiratory illness
  3. Outpatients at higher risk of influenza complications (i.e. adults 65 and older, etc.) who present with acute respiratory illness symptoms (with or without fever)

How Influenza and COVID-19 Differ

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Brandi VanValkenburg

Brandi provides personalized care as a pharmacy consultant with HealthDirect's northeastern region.  She has been serving our clients for over 10 years. 

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