They are buying time.

All pregnant women would immediately abort, it would take no longer than a week until this would be all over the news and the "health" officials and government members would be hanging from trees and street lamps and bridges.

It will take much longer for people to realize that women just won't get pregnant anymore and link this to the vaccine because not getting pregnant despite trying for a few months does not involve any dramatic events. It will eventually be detected and linked to the vaccine, but at a much later time.