Prisons stand a better chance of containment than most institutions, however, just as in any other institution, a care home for example, containment isnt always the gold that glitters. Prisons are creaking as it is and people are released daily, therefore a prison cant have perfect containment.
I know the general consensus is that prisoners should be on bread and gruel, but it's a system that has healthcare challenges at the best of times. Prison officers are at risk yet they're key workers. Likely without PPE too.
Whether we like it or not, prisoners are in the care of the state. It is a costly system.