Flu is a contagious respiratory illness (like COVID-19 and RSV) caused by influenza viruses that infect the nose, throat, and lungs.
The flu is a contagious illness that can spread quickly from one person to another. It can cause mild to severe illness, and at times can lead to death. Unlike a cold, flu symptoms start suddenly. They appear about 1 to 4 days after a person is exposed to the flu.
Symptoms of COVID-19 can be similar to flu symptoms. If you think you may have been exposed to someone with flu or COVID-19, talk with your health care provider and get tested.