The school endangered my child's health?

My 6 yo son, with Autism, was given a Flu shot at school today. The problem is....he had one 5 days ago from his Dr., the teacher had "no clue he got a shot today" (at school), my son now has a swollen and sore arm, the school nurse offered no explanation....Please advise me before I do the wrong thing? I am kinda vindictive when it comes to my reactions after my child has been put in danger, is this an appropriate time to be that way?