Compared to the common cold, influenza causes more severe symptoms and is more contagious. Antibiotics are ineffective against it, but influenza can be prevented, and vaccination is the most effective way. Currently, the immunity from the influenza vaccine generally lasts about one year. It starts to work about a month after injection, but after six months, the concentration of antibodies in the body gradually declines. Additionally, the virus mutates every year, so an annual vaccination is necessary to provide effective protection, reduce symptoms, and prevent influenza.