My Son Is 19 Years Old. He Has Crohns. He

My son is 19 years old. He has crohns. He has been on remicade infusions for 3 years now. As we were told he would be more prone to infections. This we discovered was too true for him. It seems that after every infusion (1-2 weeks after infusion he develops either a sinus infection or strep throat (with fever). This last infusion he become sicker that ever. He was just diagnosed with mono. He next infusion is October 19 of this month. I am very concerned that he infections will just keep getting worse with every infusion. By the way his crohns seem to be in check. Is there something he can take to reduce his infections?
Sincerely
Rosa