Vaccines to Reduce the Population?

This clip is from February but I figured if I missed it then you probably did to. At the influential TED conference, Bill Gates explains how we can impede global warming—reduce the number of people through “new vaccines, health care, reproductive health services.”

Here is the exact quote: “The world today has 6.8 billion people. That’s heading up to about nine billion. Now if we do a really great job on new vaccines, health care, reproductive health services, we could lower that by perhaps 10 or 15 percent.”

Um, what kind of vaccines does he have in mind that reduce the population ?