It shrank the empire so much that after the war with Persia, the Levant was heavily depopulated.

...and it was that void that the army of Mohammed filled in the rise of Islam when they conquered the Levant, Egypt, Persia, Messopotamia, and the rest of North Africa in a short period.

Those plagues tremendously changed history.

Historyofbyzantium podcast is stellar, btw.