The same thing happened in the US North East, NY, MA, CT, NJ -- the majority (e.g. over 2/3) of deaths are in long term care homes.
That is the problem to solve, lockdown or not, in most countries we have utterly failed to protect our most vulnerable people. In fact I'd go as far as arguing that lockdowns and restrictions for the general population have diverted attention and effort from protecting the LTC homes & the vulnerable.
Regardless, states other than NY also didn't prevent it getting in via staffers, visitors or delivery folks or however it got in there and have a similar, terrible LTC death toll.
As an engineer, if you gave me this problem, I'd secure every LTC home with 24hr police / national guard. All staff would be do 3 weeks on, 3 off, but while "on" (think oil rig workers), living on-site in trailers or [hm]otels, not going home every night (movies do this when filming on location; juries get sequestered for important trials, why can't we do this here?). When staff go on-shift, they must be isolated and then tested before being allowed to go onsite. Deliveries left on the loading dock and properly sanitized, and no visitors -- AT ALL. For Medical emergencies (local FD / EMTs), the resident & 1st responders would have to be isolated for triage, then taken off-site and go back through quarantine / testing to get back in.
It's totally doable and the cost is a heck of a lot less than an economic shutdown / lockdown, or the continued high death toll.
That is the problem to solve, lockdown or not, in most countries we have utterly failed to protect our most vulnerable people. In fact I'd go as far as arguing that lockdowns and restrictions for the general population have diverted attention and effort from protecting the LTC homes & the vulnerable.