This is one of the biggest culprits for why you might still get the flu after being vaccinated.
As we said above, it possible to still get the flu after getting the shot. The main two reasons are
a) the fact that you may catch a strain of the flu that was not one of the ones in the vaccine you received and
b) you may have already been exposed to the flu before you received the shot and did not yet show symptoms. The problem is that you can be infected with the flu for up to four days without showing any symptoms. And since the flu virus is essentially everywhere it is usually impossible to know where you would have picked it up. However, as we also mentioned above, having your body produce antibodies to any strain of the flu can be influential in the end (although it might not help you with the strain you were exposed to before getting the vaccine).
