[ifyoubuildit]

Presumably the under 30s will get covid within a few years, and then they will be in the pool of people with significant immunity.

[SketchySeaBeast]

Or they could vaccinate and have significant immunity nearly immediately without COVID.

[ifyoubuildit]

Yes, one of those two things will happen. The point is that the under 30s aren't likely to make it to a different age bracket where they are more significantly at risk without first achieving immunity in one of those ways.