"Lowered herd immunity meant that more children got measles, mumps and rubella"
So? What seems to be the problem with children getting rubella - a routine childhood disease so mild and quick that most people don't even notice that their children have had it?
Rubella is only dangerous for fetuses whose mothers have it for the first time when pregnant. Why can't we test girls at age 12 and vaccinate those who aren't immune?
And mumps - it doesn't cause sterility in children, only in pubescents and adults. Why can't we test boys at age, say, 7 and vaccinate those who aren't immune?
If you leave it alone, children will have these diseases early and be immune forever, just like with chicken pox. We can always test children at a later age and vaccinate then if necessary.