Incredibly unfortunate, but let’s not forget these places are not iron fortresses disconnected from the world. The staff working there every day go home every night to their families and communities. They’re shopping in the grocery store and doing all the normal daily activities even as the disease circulates. Add in visits from families, deliveries, maintenance, and all others coming and going.
The residents are generally stationary in these facilities, but everyone around them is out in the community. The person administering the vaccine is certainly not the only person from the outside coming in.
Our house was pretty much your Iron Fortress, minimal contact with the outside world, no shopping, no visits, groceries curbside delivery, then quarantined in the garage before being brought into the house, etc., etc., etc.
We all got it anyway.
Only confirmed when my nonagenarian mom needed to go to the ER for rehydration, they wouldn’t let her go without a COVID swab.
We’re out of quarantine now. I’m looking and becoming a convalescent plasma donor, if they don’t disqualify me for being too old or some other reason.