If you are susceptible to respiratory infections, can second and third hand smoke bring them on? im on ocrevus for my ms & it also makes me more susceptible to respiratory infections

Depends on details: Most people do not get noticeably increased health problems when exposed to a little second hand or third hand smoke. Of course, nobody can say anything with exactness because details vary all over the place. For example, one person might be exposed 1 day of the week while another person might be exposed 7 days of the week. Also, one person might live with 1 smoker, while another lives with 12.