I keep reading "don't kill granny".
Let's look at that further. You are 80, at home and managing without assistance, how are they gonna catch covid? OK, if they go out and about they face the same risks as everyone else, although it could be fatal to them. But if the distancing, the masks, the group limitations work (they either do, do partially, or don't - who knows?) then they should be able to catch a bus, go round a shop and have a brew in a cafe safely.
Therefore the only way they catch covid is if their family (and grand-family) bring it to their house, ie they hug and kiss, sit very close for long periods, and I've no doubt many have grandkids staying over.
So is the household the breeding ground? I don't know - but I've been out pubbing, kept myself to myself and I still don't think I've contracted Covid.