**Flu is caused by influenza viruses (mainly influenza A and B), while COVID-19 is caused by a coronavirus called SARS-CoV-2.**
They are unrelated viruses, but both spread through respiratory droplets and small particles released when an infected person breathes, talks, coughs, or sneezes. Symptoms overlap so much that you cannot reliably tell them apart without a test, though COVID-19 more often causes a loss of taste or smell and flu tends to come on abruptly with fever and body aches. COVID-19 also tends to have a longer window between exposure and symptoms, so your timeline after a known contact offers a clue rather than an answer. Testing is the only way to know which one you have, and it matters because the antiviral treatments are different. Annual flu vaccination and staying current on COVID-19 vaccination lower your chances of getting seriously ill from either.
How to tell flu from COVID
Common questions
What causes flu vs covid?
Flu comes from influenza viruses, usually influenza A or B, which change enough each year that the vaccine is updated annually. COVID-19 comes from SARS-CoV-2, a coronavirus first identified in 2019 that continues to produce new variants. The two are not related, but they infect the same airways and spread the same way, so fever, cough, sore throat, fatigue, and body aches can look identical. A test tells you which virus you have. That distinction changes treatment: oseltamivir and other antivirals target influenza, while different antivirals treat COVID-19, and both work best when started early. Call a clinician if you have trouble breathing, chest pain, confusion, or symptoms that improve then return.