> or simply old people?

So, in the early stages of the pandemic, a number of countries did exactly that. Which was, arguably, a lot more unfair; over 80s can't take a de-oldening vaccine.

Ultimately, _if_, and only if, the ICU numbers dictate either locking down the whole population or locking down that fraction of the population who have voluntarily decided to be the main contributors to ICU load... well, it's not a _great_ choice to have to make, certainly, but there's something to be said for locking down fewer people, if that is the choice.