COVID-19 or the flu?

We’re in the midst of a pandemic, and flu season is upon us. Many COVID-19 symptoms are similar to those of  influenza, which makes you wonder, How can I know if I have one or the other?

“Basically, you can’t know without testing,” says Dr. Curtiss Boyington, infectious diseases physician and general internist at the Grey Nuns Community Hospital.

With our efforts to be safe against COVID-19, we also need to know what we can do to protect ourselves against the flu, an illness that severely affects about 3,500 Canadians every year. With the ongoing pandemic and the arrival of flu season, it’s more important than ever to remember to follow public health guidelines, including the need to wear masks and maintain physical distance from others outside your home. This also includes the need to stay home when you are unwell.

Researchers continue to work on a vaccine for COVID-19. There is a vaccine available for the flu, and health officials recommend you get a flu shot every year.

To assist in navigating the differences between COVID-19 and influenza and how you can protect yourself, we turned to Curtiss to answer our questions.

How are COVID-19 and the flu similar?


COVID-19 and the influenza virus spread in similar ways and can both be spread by being in close contact with others. Both viruses spread via respiratory droplets, especially by an infected person coughing, sneezing or speaking/singing. The droplets can land on mucous membranes (in the eyes, nose or mouth), whereby the viruses gain entry into the uninfected person. As well, both viruses can be spread via infected surfaces — that is, a person touching a surface with their hands and then touching their mucous membranes (eyes, nose or mouth). From there, the viruses can spread to the lungs.

As well, both viruses can be spread if someone who is infected coughs onto a surface and, if the surface is not cleaned, another person touches the surface and transmits the virus from their hands to their mouth, nose or eyes. Also, if an infected person wipes their nose or coughs into their hands and then touches a common surface, the same process of transmission can occur.

To prevent transmission, it’s recommended that people ensure they are two metres (about six feet) apart when around others outside their home. Masks should be worn at all times when you can't maintain safe physical distancing.


COVID-19 and the flu are highly contagious and easily transmissible to others.

COVID-19 and flu common symptoms

The following are symptoms that COVID-19 and the influenza virus share:

  • Fever
  • Sore throat
  • Cough
  • Shortness of breath
  • Diarrhea (in flu, more likely in children)
  • Vomiting (in flu, more likely in children)
  • Fatigue
  • Headache
  • Nasal congestion

The symptoms of both diseases can range in severity, from no symptoms to mild or severe. Because each virus has similar symptoms, it can be difficult to diagnose which condition you have based on your symptoms alone. This is why testing and self-isolation are so important. The spread of both viruses is dangerous.

What are the differences between COVID-19 and the flu?

Although the flu and COVID-19 have similar symptoms, there are some important differences between the viruses and their potential impact on a person.

When do symptoms first appear?

  • Flu symptoms typically appear within one to four days after exposure.
  • COVID-19 symptoms typically appear between two to 10 days after exposure.


  • COVID-19 has been shown to cause a loss of taste and smell in some, but not all, cases. This symptom has not been associated with seasonal influenza.

How long will you be contagious for?

  • People with the flu usually will be contagious one day prior to symptom onset and for five to seven days afterwards.
  • Covid-19 will be contagious 10 days post-symptom onset and potentially 48 hours prior to symptom onset.

Complications that can occur

  • Influenza can lead to respiratory failure and possibly death in severe cases, particularly in the very young (infants), the elderly and pregnant women. Bacterial superinfection with pneumonia can occur with influenza.
  • In severe cases, COVID-19 can lead to severe respiratory failure and potentially death. Blood clots and multisystem inflammatory syndrome (in children) can also occur. The long-term effects of COVID-19 infection are currently being studied, since some patients display ongoing respiratory symptoms for months following infection.
  • Both viruses can cause acute respiratory distress syndrome (ARDS), stroke, heart attack, multiorgan failure and death.

What can you do to protect yourself and others?

  • Get the flu vaccine to help protect yourself, your family, your patients and your friends against influenza, which can be serious and potentially life-threatening.
  • Wash or clean your hands frequently. 
  • Maintain two metres of physical distancing.
  • Avoid large social gatherings.
  • Wear a mask at work and in indoor or outdoor environments outside the home where physical distancing can’t be maintained.
  • Isolate if you do develop any symptoms related to COVID-19 or the flu and arrange for COVID-19 testing.
  • DO NOT come to work if you are sick, since you can spread either virus to your patients, their families and your co-workers.
  • Contact your workplace, school or place you volunteer if you develop symptoms that could be related to COVID-19.

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