What is the flu? Why is a flu vaccination for children important?

The flu is a highly contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause symptoms such as fever, cough, sore throat, body aches, fatigue, and headache. Flu illness can be mild to severe, and in some cases, life-threatening. Annual influenza vaccinations are the most effective way to prevent the flu and its complications. Children, especially those under five years old, are at high risk of developing complications from the flu due to their immature immune systems.