What is influenza?

Influenza, commonly called "the flu", is a contagious disease caused by viruses that infect the respiratory tract including nose, throat, and lungs. Influenza causes severe illness and life threatening complications in many people. This document covers seasonal influenza.

What is the cause of influenza?

There are four types of viruses called influenza A, B, C and D. Influenza types A and B are responsible for the seasonal disease that occurs almost every winter. Influenza type C usually causes a very mild disease often without symptoms. Influenza type D viruses affect cattle and are not known to cause illness in people. Influenza type […]