In March 2019, Bevin said in an interview that he deliberately exposed all nine of his children to chickenpox so they would “catch the disease and become immune.”[287]

What year was that?

I mean, when I was a kid, there was no chickenpox vaccine available. I didn’t even realize that we’d finally developed one until a few years ago.

I don’t think that my parents intentionally went out of their way to expose me, though I did catch it, but intentional exposure certainly wasn’t some sort of wacko practice at the time. You were likely to catch it sooner or later, and it could be much more severe if you had it late in life — you wanted immunity earlier rather than later. Chickenpox was just kinda part of life.

searches

Looks like it was rolling out in the US in the mid-1990s.

https://en.wikipedia.org/wiki/Pox_party

Pox parties, also known as flu parties, are social activities in which children are deliberately exposed to infectious diseases such as chickenpox. Such parties originated to “get it over with” before vaccines were available for a particular illness or because childhood infection might be less severe than infection during adulthood, according to proponents.[1][2] For example, measles[3] is more dangerous to adults than to children over five years old.[1][4][5] Deliberately exposing people to diseases has since been discouraged by public health officials in favor of vaccination, which has caused a decline in the practice of pox parties,[6] although flu parties saw a resurgence in the early 2010s.[7]

In the United States, chickenpox parties were popularized before the introduction of the varicella vaccine in 1995.[9][19][20] Children were also sometimes intentionally exposed to other common childhood illnesses, such as mumps and measles.[21] Before vaccines for these infections became available, parents regarded these diseases as almost inevitable.[21]