Pretty much everybody born before 1984 had it (I've seen numbers as high as 95% of all adults). It was common practice to infect your children with it during a

Pretty much everybody born before 1984 had it (I've seen numbers as high as 95% of all adults). It was common practice to infect your children with it during a certain "safe" age range where it was just a miserable week long rash rather than a life-threatening event. There was no vaccine until then and it definitely wasn't common practice to use it on the childhood vaccine schedule until much later. Most adults having children now may not even know the vaccine exists and just assume their children will have to go through a week of the pox to get them immunity.