Flu vs. COVID-19: How to tell them apart

September 16, 2020 | by Jonathan Pinsky, MD
Categories: Healthy Driven Life

Influenza viruses become widespread each year beginning as early as mid-fall or as late as mid-spring.

When the flu is widespread, there can be more patients with severe symptoms that need hospitalization and ICU care.  This coming year’s influenza season we will also compete with COVID-19.

COVID-19 has already led to far more hospitalizations, ICU care, and death than influenza did for any of the recent past years. We need to be prepared this year for COVID-19 and Influenza.

Both the flu virus and the coronavirus are transmitted by respiratory droplets through coughing, sneezing or speaking.

The virus that causes COVID-19, SARS-2-CoV, can cause symptoms that are similar to influenza, but has other features that are unique. COVID-19 can cause any of these symptoms:

  • Fever or chills
  • Cough
  • Shortness of breath or difficulty breathing
  • Fatigue
  • Muscle or body aches
  • Headache
  • New loss of taste or smell
  • Sore throat
  • Congestion or runny nose
  • Nausea or vomiting
  • Diarrhea

So how can we tell the difference between influenza and COVID-19?

The short answer is, the only way to tell is to test for influenza virus and for SARS-2-CoV virus. The long answer is that it depends on how much virus is circulating in the community and other risk factors.

Influenza is more likely when there is a lot of influenza circulating in the community. For example, during March 2020, influenza would have been more likely because there was a lot more people infected with influenza virus in the community than with COVID-19. On the other hand, in April and May 2020, there were few to no patients with influenza, but a lot more people infected with COVID-19.

What are some characteristics of each virus?

COVID-19 is caused by infection with a new coronavirus (SARS-CoV-2) and the flu is caused by infection with an influenza virus.

  • Symptoms. Nearly everyone infected with influenza virus feels sick, but SARS-2-CoV infection can be asymptomatic in some people. Influenza virus can be mild, with just cold symptoms and fever, or can be severe with high fevers, cough and fatigue. COVID-19 infection can be asymptomatic, mild or have severe symptoms in its early stages during the first week of infection.
  • Contagious period. Influenza virus can be contagious a day prior to symptoms and last a few days on average. SARS-2-CoV virus can be contagious two days prior to the onset of symptoms and last until 10 days after the onset of symptoms. Those with asymptomatic SARS-2-COV can transmit infectious virus for no more than 10 days.
  • Complications. Risk for severe COVID-19 infection is higher for adults, rising with age, obesity, and with chronic medical conditions. Pregnancy is also a risk factor for severe influenza infection. COVID-19 hospitalizations are due to viral pneumonia and inflammation, whereas influenza hospitalizations can be due to influenza or secondary bacterial pneumonia. Unlike influenza, COVID-19 infection can trigger inflammation in the lungs days later, leading to impaired oxygen delivery to the blood, with symptoms of shortness of breath. Some patients with low oxygen levels have fatigue but no shortness of breath, a term called "silent hypoxia."
  • Testing. Looking back to the previous influenza seasons (before COVID-19), testing those with influenza symptoms was only recommended for patients at high risk for complications, or with severe illness. That is because patients with mild symptoms without risk factors are likely to improve without medications and should stay home to avoid infecting others. That was last year. This year we will need to test everyone. Here is why. If you develop flu symptoms, we won't know if it is influenza virus, another respiratory virus, or SARS-2-COV/COVID-19. If you develop symptoms, you would need to be tested for COVID-19. You may also be tested for influenza and possible other viruses if there is influenza circulating.
  • Recovery. If it is influenza, you may recover at home on your own, and go back to work or school as soon as you have no fever for one day. But if it is COVID-19, you would need to stay in isolation for 10 days, and all your close contacts would need to stay in quarantine for 14 days.
  • Vaccine. Vaccines for COVID-19 are still being studied. But there are multiple FDA-licensed influenza vaccines produced annually to protect against the three or four flu viruses that circulated in the previous year.

Why is it more important than ever to get a flu shot this year?

This year is more important than any other year to get the influenza vaccine. While you can still get the flu if you are vaccinated, during most years it provides at least 70% protection from getting the flu.

In past years, if you had the flu and had mild symptoms you did not need to be tested. This year, everyone will need to be tested for COVID-19. The more people that have flu, the more people that will need to be tested for COVID-19. Influenza infections could potentially drain testing resources for COVID-19.

More importantly, the flu shot will decrease your chances of getting severe influenza infection. The more patients that have severe flu and are hospitalized, the more it drains resources to care for patients with severe COVID-19 infection.

The influenza virus and COVID-19 can cause infection together and be more serious than either infection alone. If you get COVID-19 infection, the flu shot can prevent you from getting a more severe co-infection.

The Centers for Disease Control and Prevention recommends that all people 6 months and older get a yearly flu vaccine. September and October are good times to get vaccinated. However, as long as influenza viruses are circulating, you can still get vaccinated, even in January or later.

Until COVID-19 vaccines are widely available most of us have no immunity to the virus. The only defense we have is keeping away from others who are infected.

Masks are effective in preventing the spread of SARS-2-COV, as well as influenza and other respiratory viruses. If we do the right things to keep COVID-19 away by wearing masks, washing our hands and keeping physically distant, we may not have to get sick from influenza either.

Flu vaccines are available through your primary care physician. Contact your doctor’s office to schedule your flu shot. Find a doctor.

Our Immediate Care Centers and Walk-In Clinics also offer flu shots. No appointment needed. Walk in any time. Check locations and wait times.

At Edward-Elmhurst Health, your safety and well-being continue to remain our top priority. Learn more about our Safety Commitment.

For updates on our planning and response efforts as we work to stop the spread of COVID-19, please check EEHealth.org/coronavirus.


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