Influenza (also known as flu) is a contagious respiratory
illness caused by influenza viruses that infect the nose,
throat and lungs. Flu is different from a cold, and usually
comes on suddenly. Each year flu viruses cause millions
of illnesses, hundreds of thousands of hospital stays and
thousands or tens of thousands of deaths in the
United States.
Flu can be very dangerous for children. CDC estimates that
between 6,000 and 26,000 children younger than 5 years
have been hospitalized each year in the United States
because of influenza. The flu vaccine is safe and helps
protect children from flu.