[mlyle]

It doesn't have to do with the percentage who die, but rather the variation in susceptibility.

If 2% of people are 80% likely to die from COVID, and the rest have a baseline 0.1% risk. Assume prior infection provides no protection:

* 1000 (of whom 20 are particularly vulnerable) people are naturally infected; .001 * 990 =~ 1 people of average susceptibility die; 16 maximally susceptible people die. Total of 17 deaths.

* Then, you are left with 983 people, (of whom 4 are particularly vulnerable). Upon reinfection, .001 * 983 =~ 1 person of average susceptibility dies; 3.2 people of high susceptibility die. There's a total of ~4 deaths.

This is a 4x reduction in deaths even if there's no protection from prior infection.