The influenza virus mutates so fast that even if the vaccine is updated every year, there is no guarantee that the vaccination will cover all the seasonal epidemic. Influenza vaccination does not guarantee a 100% protection against influenza, and may also lead to side effects such as low fever in vaccinated people. Therefore, there is no need to be vaccinated against influenza.
People who have recovered from the disease can gain a certain degree of immunity and will not be affected by the same flu virus again within 1 year does not effectively refute the above conclusion.