September 18, 2020

This flu season may look different than any we have had before. The combination of a global pandemic and flu season happening at the same time may lead to confusion since there are many similarities between influenza and COVID-19. Some of these similarities include patients who are asymptomatic to those experiencing severe onset of symptoms.  Particularly challenging for patients and physicians is that COVID-19 and influenza share so many common symptoms.

Shared symptoms for flu and COVID-19:

  • Fever or feeling feverish/chills
  • Cough
  • Shortness of breath or difficulty breathing
  • Fatigue (tiredness)
  • Sore throat
  • Runny or stuffy nose
  • Muscle pain or body aches
  • Headache
  • Some people may have vomiting and diarrhea, though this is more common in children than adults

Currently, there is only one known symptom that separates the two.

"The loss of sense of smell or taste is a different sign with COVID-19," said Dr. Sarah Boyd, Infectious Diseases Physician at Saint Luke’s Health System. "Sometimes you can see vomiting and diarrhea with the flu, especially in kids. Until we see what kind of flu we are working with this year, everything kind of overlaps a bit."

There might be another way to help determine what illness you may have.

"The course of the two illnesses differ in their onset," said Dr. Marc Larsen, Emergency Physician and director of operations for Saint Luke's Health System's COVID-19 response team. "Headaches, fever, body aches, and coughs are more of the hallmark signs of influenza in an abrupt onset. With COVID-19, it is a little, but more gradual, drawn-out process and longer course of illness."

According to the Centers for Disease Control and Prevention (CDC), if a person is infected with COVID-19, they develop symptoms in about five days after infection but can appear anywhere from 2-14 days, while signs of the flu show up 1-4 days after infection. 

Many people may not realize that it is possible to be infected with both influenza and COVID-19 at the same time. 

"I think we were thrown a little bit when COVID-19 arrived in March, the co-infection rate of influenza and SARS-CoV-2 were thought to be very low," said Larsen. "Meaning if you thought you had the flu, you likely do not COVID-19. That thought was some-what disproven as flu ended and COVID-19 ramped up. I don't think we will have that anchoring bias of, 'oh, you have influenza, that means you don't have COVID-19.' We are starting to think you can have co-infection."

How it Spreads

"COVID-19 and influenza are spread the same way. It happens mainly from droplets made by people infected. If they are in close contact with others, within about 6-feet, and they sneeze, cough, or release droplets when they talk, they can infect others," said Dr. Boyd. "It is when these droplets spread into the air and land on others' nose or mouths, the virus spreads."

Also, it is possible to get infected with the viruses when you touch a surface that hasn't been cleaned and could have the virus on it or have physical contact with an infected person – by shaking hands or high-fiving.

This is where hand-hygiene and cleanliness become an essential factor in staying healthy.


According to the CDC, you can spread influenza and COVID-19 virus's a full day before experiencing symptoms yourself.

There are some differences in the time that a person is contagious with the virus.

We are here to help break it down:

  • Flu
    • Older children or adults are the most contagious in the initial 3-4 days of illness
    • People can remain contagious for up to a week
  • COVID-19
    • It is possible to spread the illness up to two days before experiencing symptoms
    • A person can remain contagious for at least ten days after signs or symptoms first appear
    • It is still possible to spread the virus if someone is asymptomatic or their symptoms have disappeared for at least ten days after testing positive

Here is another important differentiator to keep in mind. Though they are spread in the same way, COVID-19 is considered to have more "superspreading" events than the flu, infecting more people more easily, resulting in a continuous spread as time goes on.

High-Risk Populations

The flu and COVID-19 illness can affect these groups of people with more severity and greater complications:

  • Older adults
  • Those with underlying health conditions
  • Pregnant women or people who are immunocompromised

With the flu, younger children are at higher risk for severe illness. According to the CDC, School-aged children infected with COVID-19 are at higher risk of Multisystem Inflammatory Syndrome in Children (MIS-C), a rare but severe complication of COVID-19.

What Do I Do if I Think I Have Influenza or COVID-19

"It is going to be difficult to simply look at a person's symptoms and know what they should be tested for. So, we will likely be testing for both COVID and flu when someone presents with symptoms that could be either illness," said Dr. Boyd. "Whether they are at convenient care or emergency room, or physician practice or urgent care, this year looks like we will be testing for both at the same time." “Testing is important for both contact tracing with COVID-19 if was positive and for treatment options if is influenza.”

What Can I Do to Protect Myself?

The most important thing you can do this year is to get your flu shot and continue with recommended public health measures including wearing masks, social distancing, hand washing, and staying home if you think you may be sick. Everyone six months and older are highly encouraged to get this year's vaccine.

There are a few different doses of the flu vaccine. The standard dose is the quadrivalent flu vaccine. According to the CDC, this vaccine is for people six months and older. The high-dose shot is the trivalent flu vaccine, which is approved for people 65 and older. 

When Should I Get My Flu Shot?

"The influenza vaccine is often given in September and October and you definitely want the vaccine completed by the end of October," said Dr. Boyd. "You do have to have a couple of weeks to get the immunity. Therefore, you have to factor that in when getting your vaccine."

"The biggest concern I have is that doing what we have been doing the last six months is going to be really challenging, and people are going to start letting up," said Dr. Larsen. "But, it's the most important thing to do as we move into the next six months of this process. The more we get lackadaisical on our masking and social distancing, the more flu is going to be prevalent, and the more COVID-19 will be around."

Saint Luke’s has many options available to make getting your flu shot easy and at a location close to home through Saint Luke's Primary Care and Saint Luke's Convenient Care.