hi tnm, you should be able do lots to support your immune system without jeopardizing your job. i work around hundreds of kids daily and since i started working on my underlying health via nutrition, i don't get colds any more. i can feel it when a virus is trying it on, but generally it doesn't stand a chance against my body's natural defenses. my worst case scenario at this stage is pretty much the sniffles.
that said, we are all different. i personally do not ascribe to autoimmune causality when it comes to ms. not to say it's not a factor, but that the autoimmune aspect is one part of a larger set of imbalances that should be addressed systemically rather than medicated in a piecemeal, band-aid fashion. so i have never taken immune system suppression drugs. vitamin d3 did a big chunk of that work for me, among other things. there should be plenty of others here who can advise on how to protect yourself when dealing with a drug-compromised immune system.
lots of info on ms and nutrition all over the place. my experience and intro here regimens-f22/topic2489.html
my approach: no meds so far - just nutrient-dense anti-inflammatory whole foods, and supplements where needed
info: www.whfoods.com, www.nutritiondata.com