Shingles literally is the chickenpox virus, but it's a reoccurrence of the virus after it has lain dormant for years and years. The body's immune system still basically remembers how to fight the virus, so it doesn't hit as bad and manifests as shingles instead.
The first time I heard of shingles as a medical condition I laughed. The person who had it failed her college exams because of it. So again, stress seems to have been an issue.
Anyway I laughed and everyone in the group said "you're a prick seanc, shingles is really serious". I did feel like a prick.
A cursory look at the link in that link says all the people got it after their first dose and were female and most had some kind of rheumatoid arthritis. I got the pfizer as well, but I don't fit into that group, so phew.