Compared with most other viral respiratory infections, such as the common cold, influenza (flu) infection usually causes a more severe illness with a mortality rate (death rate) of about 0.1% of people who are infected with the virus. Cold symptoms (for example, sore throat, runny nose, cough (with possible phlegm production), congestion, and slight fever) are similar to flu symptoms, but the flu symptoms are more severe, last longer, and may include vomiting, diarrhea, and cough that is often a dry cough.

The following table is provided by the CDC to help distinguish between a cold and influenza: