An interesting short video.
Useful to read this too: Biological Warfare at the 1346 Siege of Caffa.
Although medics may not have had a name for the vector of the disease, they did suspect aspects of its transmission, hence the plague doctor beak masks filled with herbs to "cleanse" the foul stench in the air. They were wrong - the fleas didn't care much for the masks.
Other videos here and here, with various levels of annoyance.
This is a much longer and better documentary, with a focus on the plague in London, 1665. A year later, the city was cleansed in an inferno, that also killed the infecting rats and fleas, that were, astonishingly, not considered the primary source of the plague(s).
Notice what a REAL pandemic looks like.