The disease commonly known as the flu is influenza. Influenza is a contagious viral infection that primarily affects the respiratory system, leading to symptoms such as fever, cough, sore throat, body aches, and fatigue. It can lead to more severe complications, particularly in vulnerable populations such as the elderly, young children, and those with underlying health conditions. Vaccination is one of the best ways to prevent influenza, as the virus can change from season to season. Annual flu vaccines are recommended to help protect against the most prevalent strains.