A vaccine does not fight anything for you. It shows your immune system a picture, so it can practise before the real thing arrives.
Sources
US Centers for Disease Control and Prevention — Misconceptions About Seasonal Flu and Flu Vaccines: flu shots are made with inactivated viruses or a single influenza protein, the virus in them is not active, and an inactive virus cannot transmit disease
US Centers for Disease Control and Prevention — Key Facts About Seasonal Flu Vaccine: the vaccine prompts antibody production, and protection declines over time so annual vaccination is needed