Gates: How to lower the Earth's supply of C02

"One way is to lower the Earth's population", according to Bill Gates.




"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!" (About 1 Billion People!)"

Hey wait a minute!
How would new vaccines lower the earth's population?