It could also be because people got contaminated IN vaccination centers when coming for their first vaccine dose. Told from a doctor working in Israel.
The vaccination locations are the largest group of people anyone I know how been around in a year. Dozens of people coming in and out of a room every 15 minutes, plus having to sit next to strangers for 15 minutes to make sure you don't have an adverse reaction is a larger risk than most take ever.
I've worked several full days at a vaccination center in Michigan. It's quite crowded, something like a grocery store. It wouldn't surprise me if there was some spread there.
