Ds had his 18 month vac ( measles, mumps, rubella and chicken pox) yesterday at the bottom of his lip a little sore appeared. Looks a bit like a cold sore. We haven't had a cold sore and he hasn't been in contact with anyone with one. Just wondering if this is something to do with the vac or it could be a cold sore. I have a newborn so am trying to keep him from touching hands/ face and kissing him which is easier said than done. Any advice or anyone had this happen after the vac?