First, we've got population. The world today has 6.8 billion people. That's headed 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.
https://www.ted.com/talks/bill_gates_innovating_to_zero/transcript?language=en
the Gates apologists will say he was talking about families who have tons of kids because of infant mortality, so they end up having lots of "spare" kids thus running up the population.
So Vaxx will alleviate the "Fear" thus cutting back on the spare kid methodology.
When you figure out who BG's parents are, though, there's no way to spin his comment.