You are getting a flu shot with the latest mutations of the virus. Your body learns how to battle those viruses by creating antibodies and you become "immune" against them.
The Influenza virus is one of the most quick mutating virus on earth (same is valid for common cold).
Because of this - there is no guarantee you are immune to all mutations. There is always risk of a new mutation spreading like pestilence.
And you know - it takes only one sneeze around you to get infected.
Me - I am oposing this kind of shot.
The flu takes a week to battle by a strong healthy person. Why should I poison myself with a shot filled with dormant half-dead viruses (killed with mercury)?
Tea, hot soup and some rest will do the job just fine. You only need to be aware for complications.