My colleague is sick but is still coming into work. Am I overreacting??

I’ll keep it brief. I work in an office and we have an event tomorrow. My colleague has covid at the moment but he told our boss that he might try and come in tomorrow for the event if he feels better. Am I the only one that sees this as irresponsible? I have a vulnerable family member. I offered to help out tomorrow but if he is there, I don’t want to be anywhere near him but it’s inevitable. I’m going into a different office tomorrow and if he’s not in, I will travel during my lunch to help out but if he is in, I’m not gonna bother. Am I overreacting?