What is the Difference Between Flu and COVID-19?

Influenza (flu) and COVID-19 are both contagious respiratory illnesses, but they are caused by different viruses. COVID-19 (coronavirus) and the flu have many similarities and differences. The only way to truly diagnose whether you have the flu or COVID-19 is through testing. But knowing the symptoms of each can help you determine what to do next. Below, we provide an overview of both viruses, similarities and differences between symptoms.

COVID-19 and flu causes

COVID-19 and the flu are caused by different viruses. COVID-19 is caused by a coronavirus called SARS-CoV-2, while flu is caused by influenza A and B viruses.

COVID-19 and flu spread and severity

COVID-19 appears to be contagious for a longer time and to spread more quickly than the flu. With COVID-19, you may be more likely to experience loss of taste or smell. Severe illness is more frequent with COVID-19 than with the flu. Compared with historical flu cases, COVID-19 may cause more hospital stays and death for people age 18 and older, even those who have no other health challenges.

COVID-19 and flu symptoms

Symptoms of COVID-19 and the flu appear at different times and have some differences. COVID-19 symptoms generally appear 2 to 14 days after exposure. Flu symptoms usually appear about 1 to 4 days after exposure. Possible symptoms include:

Flu 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.

COVID-19 Symptoms

• Fever or chills
• Cough
• Shortness of breath or difficulty breathing
• Fatigue
• Muscle or body aches
• Headache

COVID-19 and flu complications

COVID-19 can cause different complications from the flu, such as blood clots, post-COVID conditions and multisystem inflammatory syndrome in children. Flu infection leads to secondary bacterial infection more often than COVID-19 infection does.