The protective effect of the flu vaccine starts about two weeks later.
Therefore, it is preferable to administer the flu shot just before the period in which the seasonal influenza epidemics occur, that means within the months of October or November. However, if the epidemic has not yet begun that year, a vaccine can be made until December. The protection of the vaccine is estimated to be around six to eight months, but in the elderly it is usually less. If the vaccine is done too early, it may have lost its protection during the flu season.