When my oldest child was little they weren't giving the chicken pox vaccine yet (thank goodness because he was injured enough), and at 18 months he got chicken pox. His immune system was a mess and he got a bad case. I can remember they were in his mouth :( Even still, he was pretty much a happy baby, it's not like that bad case was keeping him down. Anyway... over a decade later my youngest gets chicken pox. My youngest is unvaccinated because of his brother's injuries. He had a mild case that lasted three days and now has life long immunity. I'd never seen a case of pox come and go so easily without issue, without scarring, my youngest didn't even slow down. He was bummed that I made him stay home a few days because he felt fine.
We were born with immune systems that work beautifully if we support them with proper nutrition and don't inject our kids full of toxins.