You dont have to look that far back. Just look at the 1918 Influenza. It wiped out between 20-50 million. When you dont know the tens of millions it killed...that is a big deal.
I am comparing the novel aspect of the virusnot the results.
Historically, this happened pretty often. Travel and communication has changed to the point where transmission takes days instead of weeks and months. That is what makes it unquie.
And why people will study the viral aspect (pun kind of intended) of the social impact of this for decades.