Because of the advancements of medicine, we have not recently had any experience with pandemics. I don't know how many remember the polio outbreak in the 1950s. But pandemics were common in the past. Cholera, the plague, etc. used to routinely break out. The schools around London were closed in the 1640s due to, I believe, the plague. Pandemics may be a "normal' thing for along time in the future. They seem to have some kind of regularity to them.