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Influenza (flu) and COVID-19 are both contagious respiratory illnesses, but they are caused by different viruses. COVID-19 is caused by infection with a coronavirus (SARS-CoV-2) first identified in 2019. Flu is caused by infection with a flu virus.

Compared with flu, COVID-19 can cause more severe illness in some people. Compared to people with flu, people infected with COVID-19 may take longer to show symptoms and may be contagious for longer periods of time.


Both COVID-19 and flu can have varying degrees of symptoms, ranging from no symptoms (asymptomatic) to severe symptoms. Common symptoms that COVID-19 and flu share include:

  • Fever or feeling feverish/having chills

  • Cough

  • Shortness of breath or difficulty breathing

  • Fatigue (tiredness)

  • Sore throat

  • Runny or stuffy nose

  • Muscle pain or body aches

  • Headache

  • Vomiting

  • Diarrhea (more frequent in children with flu, but can occur in any age with COVID-19)

  • Change in or loss of taste or smell, although this is more frequent with COVID-19.


If a person has COVID-19, it could take them longer from the time of infection to experience symptoms than if they have flu. Typically, a person may experience symptoms anywhere from one to four days after infection. A person may experience symptoms anywhere from two to five days, and up to 14 days after infection.

  • On average, people can begin spreading the virus that causes COVID-19 2-3 days before their symptoms begin, but infectiousness peaks one day before their symptoms begin.

  • People can also spread the virus that causes COVID-19 without experiencing any symptoms.

  • On average, people are considered contagious for about eight days after their symptoms began.

How it spreads:


Both COVID-19 and flu can spread from person to person between people who are near or in close contact with one another. Both are spread mainly by large and small particles containing virus that are expelled when people with the illness (COVID-19 or flu) cough, sneeze, or talk. These particles can land in the mouths or noses of people who are nearby and possibly be inhaled into the respiratory tract.  In some circumstances, such as indoor settings with poor ventilation, small particles containing virus might be spread longer distances and cause infections.

Most spread is by inhalation of large and small droplets; however, it may be possible that a person can get infected by touching another person (for example, shaking hands with someone who has the virus on their hands), or by touching a surface or object that has virus on it, and then touching their own mouth, nose, or eyes.


While the virus that causes COVID-19 and flu viruses are thought to spread in similar ways, the virus that causes COVID-19 is generally more contagious than flu viruses. Also, COVID-19 has been observed to have more superspreading events than flu. This means the virus that causes COVID-19 can quickly and easily spread to a lot of people and result in continual spreading among people as time progresses.

The virus that causes COVID-19 can be spread to others by people before they begin showing symptoms, by people with very mild symptoms, and by people who never experience symptoms (asymptomatic people).

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