If your child isn't a huge fan of needles, he won't like this. To combat chicken pox, experts now recommend two shots instead of one — the first between 12 and 15 months and a second between 4 and 6 years. A study in the New England Journal of Medicine found that the immunizing effects of the varicella vaccine, a childhood shot routine since 1995, may eventually wear off in some youngsters — the more time since the shot, the worse the bout can be.