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Because some of the symptoms of flu, COVID-19, and other respiratory illnesses are similar, the difference between them cannot be made based on symptoms alone. Testing is needed to tell what the illness is and to confirm a diagnosis.

The flu and COVID-19 are both contagious respiratory illnesses, but they are caused by different viruses, according to the Centers for Disease Control.

COVID-19 is caused by infection with a coronavirus first identified in 2019, and flu is caused by infection with influenza viruses.

COVID-19 seems to spread more easily than flu.

Compared to flu, COVID-19 can cause more serious illnesses in some people. COVID-19 can also take longer before people show symptoms and people can be contagious for longer.

Because some symptoms of flu, COVID-19, and other respiratory illnesses are similar, the difference between them cannot be made based on symptoms alone. Testing is needed to tell what the illness is and to confirm a diagnosis.

People can be infected with both flu and the virus that causes COVID-19 at the same time and have symptoms of both influenza and COVID-19.

Signs and Symptoms

Similarities: Both COVID-19 and flu can have varying degrees of signs and 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 and diarrhea

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

Flu Symptoms

The flu can cause mild to severe illness, and at times can lead to death. Flu is different from a cold. Flu usually comes on suddenly. People who have flu often feel some or all of these symptoms:

• Fever or feeling feverish/chills

• Cough

• Sore throat

• Runny or stuffy nose

• Muscle or body aches

• Headaches

• Fatigue (tiredness)

• Some people may have vomiting and diarrhea, though this is more common in children than adults.

  • It’s important to note that not everyone with flu will have a fever.

Symptoms of COVID-19

People with COVID-19 have had a wide range of symptoms – ranging from mild symptoms to severe illness. Symptoms may appear 2-14 days after exposure to the virus. Anyone can have mild to severe symptoms. People with these symptoms may have COVID-19:

• 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

This list does not include all possible symptoms. Older adults and people who have severe underlying medical conditions like heart or lung disease or diabetes seem to be at higher risk for developing more serious complications from COVID-19 illness.

How Long Symptoms Appear After Exposure and Infection

Similarities: For both COVID-19 and flu, 1 or more days can pass between when a person becomes infected and when he or she starts to experience illness symptoms.

Differences: If a person has COVID-19, it could take them longer to experience symptoms than if they had flu.

Flu

Typically, a person experiences symptoms anywhere from 1 to 4 days after infection.

COVID-19

Typically, a person experiences symptoms about 5 days after being infected, but symptoms can appear 2 to 14 days after infection.

How Long Someone Can Spread the Virus

Similarities: For both COVID-19 and flu, it’s possible to spread the virus for at least 1 day before experiencing any symptoms.

Differences: If a person has COVID-19, they could be contagious for a longer time than if they had flu.

Flu

Most people with flu are contagious for about 1 day before they show symptoms.

Older children and adults with flu appear to be most contagious during the initial 3-4 days of their illness, but many people remain contagious for about 7 days.

Infants and people with weakened immune systems can be contagious for even longer.

COVID-19

How long someone can spread the virus that causes COVID-19 is still under investigation.

It’s possible for people to spread the virus for about 2 days before experiencing signs or symptoms (or possibly earlier) and remain contagious for at least 10 days after signs or symptoms first appeared. If someone is asymptomatic or their symptoms go away, it’s possible to remain contagious for at least 10 days after testing positive for COVID-19. People who are hospitalized with severe disease and people with weakened immune systems can be contagious for 20 days or longer.

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