Although COVID-19 and the flu are caused by different viruses, they can appear to be similar respiratory illnesses. Similarities in symptoms make it hard to tell the difference between them, so the only way to truly diagnose whether you have the flu or COVID-19 is through testing. However, while Flu and COVID-19 share many characteristics, there are some key differences between the two. Below we provide an overview of COVID-19 and flu, and outline their key similarities and differences between symptoms, transmissions, contagion periods, and more.  

1. COVID-19 and flu have similar symptoms, but COVID-19 seems to cause more serious illness in some people.

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/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

What's the difference?

COVID-19 seems to cause more serious illnesses in some people. Other signs and symptoms of COVID-19, different from flu, may include change in or loss of taste or smell.

2. If a person has COVID-19, it could take them longer to develop symptoms than if they had the flu.

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

What's the difference?

With flu, typically a person develops symptoms anywhere from 1 to 4 days after infection.

With COVID-19, typically a person develops symptoms 5 days after being infected, but symptoms can appear as early as 2 days after infection or as late as 14 days after infection.

3. If a person has COVID-19, they may be contagious for a longer period of time than if they had flu.

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

What's the difference?

With flu, most people 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 remain contagious for about 7 days.

With COVID-19, it’s possible for people to spread the virus for about 2 days before experiencing signs or symptoms 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.

4. COVID-19 is generally more contagious.

Both COVID-19 and flu can spread from person-to-person, between people who are in close contact with one another (within about 6 feet). Both are spread mainly by droplets made when people with the illness (COVID-19 or flu) cough, sneeze, or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.

What's the difference?

COVID-19 is more contagious among certain populations and age groups than flu. Also, COVID-19 has been observed to have more super-spreading events than flu. This means the virus that causes COVID-19 can quickly and easily spread to a lot of people and result in continuous spreading among people as time progresses.

5. Most people who get flu will recover in a few days to less than two weeks, while those with COVID-19 are more likely to develop complications.

Both COVID-19 and flu can result in complications, including:

• Pneumonia
• Respiratory failure
• Acute respiratory distress syndrome (i.e. fluid in lungs)
• Cardiac injury (e.g. heart attacks and stroke)
• Worsening of chronic medical conditions (involving the lungs, heart, nervous system or diabetes)
• Inflammation of the heart, brain or muscle tissues

What's the difference?

With flu, most people will recover in a few days to less than two weeks, although some people will develop complications.

With COVID-19, additional complications can include:

• Blood clots in the veins and arteries of the lungs, heart, legs or brain
• Multisystem Inflammatory Syndrome in Children (MIS-C)

6. There are currently no treatments or vaccines for COVID-19 like there are for the flu.

For both COVID-19 and flu,  people at high-risk of complications or who have been hospitalized for COVID-19 or flu should receive supportive medical care to help relieve symptoms and complications.  Vaccines for both illnesses must be approved or authorized for emergency use by the FDA.

What's the difference?

For flu, there are FDA-approved influenza antiviral drugs to treat the virus. There are also multiple FDA-licensed influenza vaccines produced annually to protect against the 3 or 4 flu viruses that scientists anticipate will circulate each year.

For COVID-19, there are currently no drugs or vaccines approved by the FDA to prevent or treat COVID-19. Researchers and manufacturers are expediting the development of a vaccine to prevent COVID-19.

While symptoms and transmission of flu and COVID-19 are similar, there are some key differences between the two respiratory illnesses. COVID-19 seems to spread more easily than flu and causes more serious illnesses in some people. It can also take longer before people show symptoms and people can be contagious for longer. Another important difference is there is a vaccine to protect against flu. There is currently no vaccine to prevent COVID-19, although there is a possibility that one may be available before the end of the year. If you're feeling sick and unsure of whether it's COVID-19 or flu, the only way to know for sure it to get tested.