Some people may get stronger immune respond to the shot so will get flu like symptom which means they are producing more antibodies against the flu particles in the vaccine
Would highly recommend getting flu shot
The flu vaccine causes antibodies to develop in your body about two weeks after you get it. These antibodies provide protection against infection with the viruses that are in the vaccine.
More info: https://www.medicinenet.com/flu_vaccination/article.htm#influenza_vaccine_flu_shot_facts