User blog comment:Essie Essex/Arkane Studios Announces Dishonored 2/@comment-27202257-20150615040025/@comment-1500935-20150615104950

Bethesda wrote this on their blog:

"Dishonored 2 is set 15 years after the Lord Regent has been vanquished and the dreaded Rat Plague has passed into history."

I'm not sure if it means Piero and Sokolov cured the plague or if it just faded in history.