The flu vaccine is a medical preparation designed to protect against the influenza virus, which causes seasonal flu. It works by stimulating the immune system to produce antibodies that can fight off the virus. The vaccine is typically administered annually, as the virus can change from year to year. Receiving the flu vaccine can help reduce the risk of severe illness, hospitalization, and death from the flu. It is recommended for most people, especially those at higher risk, such as the elderly, young children, and individuals with certain health conditions.