Residents are generally under 34 and in good heath. In the USA, only ~2400 people 34 have died from COVID--and that is mostly people with comorbidites.
In comparison about ~250,000 people over 55 have died.
You'd obviously have do account for life-years lost, risk of exposure [1], etc. I wouldn't be shocked if giving the vaccine to a 25 year old resident is a sub-optimal choice.
[1]Based on my MiL's experience (an ER doc), the risk of infection at a hospital is a lot lower than it used to be because they have PPE now. She's more worried about catching it from her son who works in an office. That said, they need to take into account risk of exposure and risk that the residents spread it to others.