Two things...
1. The Plague, yrsenia pestis, comes in three forms (not sure if he covered this)
a. Bubonic, which is transferred through blood to blood contact
b. Spetisemic, which is transferred through drinking and bathing water
And
c. Pneumonic, which is transferred by sneezing, coughing, and even just breathing.
The first two have between 25-50% mortality if untreated, which is super bad.
The pneumonic variant, though... is about 90% mortality, and kills in about 4-6 hours. Kids would be playing outside, one of them would sneeze, and 4 hours later all of them would be dead. Entire villages were wiped out in a day in 1360, all over Europe, and to this day Europeans and Americans say "bless you" when people sneeze because it was long ago assumed that a sneeze meant death in a few hours.
It was so bad, we still say stuff from the 14th century that's been seared into the collective memory of Western Europe.
And all it takes is streptomyces medications to prevent it and save you..
Which brings me to my second point
2. If only it was this easy to get people to listen to epidemiologists when it came to diseases.
Pharma has it so easy, not dealing with Americans....