They do help indirectly - by innoculating the 90% who can take a vaccine, the 10% who can't (for example babies when it comes to measles vaccines) are unlikely to actually catch the disease.
Oh, for sure, I wasn't trying to say vaccines shouldn't be used! They are extremely important to a healthy population overall, and it is all the more important for people with healthy immune systems to get them to help protect those that can't benefit directly.