vaccine question

Li
My son had his 18 month appointment June 2nd and had the high fever for over a week as a reaction. This was take  yesterday. The site of the injection has stayed red. It does not raise up and it does not have a hard knot under it. I asked the pediatrician and he saod he has never seen that before but was jot at all concerned by it. Has anyone experienced a similar reaction? Or have any words of wisdom?