Epidemiologists actually STUDIED this to see how ppl would react to an epidemic irl
The problem was that it DIDN'T go away when the raid ended. Your char had to be high leveled to survive for a certain time till it went away on its own, or your char died
If you called off a pet, and summoned it again it STILL had the debuff, and that was how it spread
Low leveled chars died quickly. There were literally bodies lying in towns.
Many of the players did not take it seriously and did not self-quarantine and spread it even further.
There are news out there of people deliberately infecting others after being told to self-quarantine. Not life imitating art; more like art reinforcing life.
WOW wound up reverting the server cause they couldn't completely clean up the bug.