Honestly, at 6 months old, most babies aren't finished with vax series anyhow, so little/no immunity is likely to happen. Take precautions you would take for ANY young infant in public places.
My thoughts are that you can't keep you kids in a bubble. If not vaxing will cause you so much anxiety that you keep your kids from experiencing the world, then it's just not worth it. Most who don't vax or who selectively vax do so because they think it is SAFER to not vax or selectively vax, and then take alternative precautions (frequent hand washing, natural protection, etc.). You have to do what you think will keep your kids the safest without having to keep them in a bubble. We took our partially vaxed DS to Vietnam when he was 3. He was vaxed for those conditions I was extremely worried about and for the rest, we took other precautions. But in no way did we leave him home just because he *could* catch something.
~Brandon Michael (11/23/03), Jocelyn Lily Nữ (2/4/07, adopted 5/28/07 from Vietnam), Amelia Rylie (1/14/09), & Ryland Josef William (9/7/05-9/7/05 @ 41 wks).