Influenza (flu) and COVID-19 are contagious respiratory illnesses caused by viruses. Depending on the variant, COVID-19, caused by the SARS-CoV-2 virus, may be more easily spread than the flu and can cause more severe illness, including long-term symptoms. Compared to the flu, COVID-19 has a longer incubation period (time from when you’re first exposed to when you develop symptoms) and contagious period (time when you can spread the disease to other people). Because COVID and the flu can have some of the same symptoms, specific testing is needed for a definitive diagnosis. Treatments and approved vaccines are available for both COVID-19 and the flu, although the specific antiviral treatments and vaccines differ.