Nearly every girl will have sex at some time in her life.
It doesn't matter if neither they or their partner have been promiscuous.
And the parents don't get to pick who the partner is or what kind of history he had. It may be someone who was once messed up, but set himself right before meeting her.
I agree that parents should get to make the call on this for their kids, but IMHO a vacination against a disease is not encouragement to expose yourself to that disease. I never went looking for someone with smallpox to go play with.