Well if someone got a mild case of it as a kid, they can still get a case of it as an adult. I remember working in the hospital, we had a few extreme chickenpox cases and my coworkers would argue about who would go into isolation to deal with the patient. Since I had an extreme case as a kid, chances are really low to none that I would get it again so I would always go. I actually had one older coworker who had never gotten a case of it. They say it is worse to get as an adult than as a kid. I guess that's why they use to have those chickenpox parties when we were kids.
Re: Chickenpox exposure at work.
I haven't seen anyone walking around with masks or scratching themselves, lol. I think the offender has been ordered to stay home!
And yes, it could potentially be harmful, depending on when in the pg you contract it.
https://www.mayoclinic.com/health/chickenpox-and-pregnancy/HO00036