I believe the worry was twofold: 1) That people who couldn't be vaccinated would get the virus later in life (because it would be less common), when it's a muc

I believe the worry was twofold: 1) That people who couldn't be vaccinated would get the virus later in life (because it would be less common), when it's a much more serious illness. 2) That there was a protective effect against shingles from having people regularly encounter the disease by encountering children with chicken pox. But it turns out that the latter isn't actually an issue.