the point is - you make your own choices, and let others make theirs. there shouldn't be an "opt out" clause on this, there should be an "opt in" clause.
Normally, I would agree with you about this sort of thing, but the girls who are at the highest risk of this probably have parents who never would opt in. "Parents" is probably being generous, since dad might not well live there.
You're certainly smart enough to opt out if you think that's a great decision, but the default ought to be to get the vaccine.