The influenza vaccine is a medical preparation designed to protect against the influenza virus, which causes the flu. It works by stimulating the immune system to recognize and fight the virus, reducing the risk of illness. The vaccine is typically administered annually, as the virus can change from year to year. There are different types of influenza vaccines, including inactivated vaccines, which contain killed virus, and live attenuated vaccines, which contain weakened virus. Vaccination is recommended for most people, especially those at higher risk, such as the elderly, young children, and individuals with certain health conditions.