How to keep toddler from getting newborn sick

Ra

My 2 year old started coughing and vomiting last night and I’m nervous he’s coming down with something (I’ll be calling the dr in the am). He started school in September and it seems like he’s been sick every two weeks. Now with a 2 week old newborn at home, I’m wondering how I can keep her from catching whatever it is that he keeps bringing home from school? Any tips would be greatly appreciated!