Even if 100% of the dead are in the risk/old group (which is not true), it's hard to achieve a 99% reduction with a 95% efficient vaccine. For that to work, you

Even if 100% of the dead are in the risk/old group (which is not true), it's hard to achieve a 99% reduction with a 95% efficient vaccine. For that to work, you have to assume that the main way of infection is from inside the group. I think this is highly unlikely in a scenario where you say: protect the weak, let everybody else just get it.