Not wishing to trivialise what we all believe to be a very worrying situation but have to ask “is it being so cheerful that keeps you going”.Back on topic, and not trying to upset anyone any more but I'm minded of the (original 1970's) BBC series Survivors where a dreadful "new" contagion is spread so rapidly around the globe with lightning speed, facilitated by increasingly easy travel.
As OC rightly points out these new infections do appear with regularity. Thankfully most of them are (relatively) benign and, once the vast majority who might catch it have gained natural resistance any epidemic subsides. It is historical fact that, when the Conquistadors first arrived in central and south America, the measles that they brought with them and to which most Europeans were moderately resistant, was at first catastrophic for the resident population.
We are fortunate that the vast majority of these newly evolved "bugs" are (in most cases) not too life threatening save for the already weak or I'll - sad though that is. And (I can't recall who wrote it) but I recall reading the very true observation once that a pathogen that wipes out its host is NOT a very successful one in the long run.
Unfortunately once every few centuries a variety of disease breaks out that is so virulent and widespread that (for a time) it breaks the previously stated rule and causes huge scale wipe-outs. Back in the medieval times such "plagues" tended to take years, or even decades, to spread. Even the 1918 "Spanish Flu", although dreadfully severe, spread relatively slowly - although undoubtedly hastened by the repatriation of the brave survivors of WW1 which was, still, a relatively slow process.
Nowadays anyone with the means and desire can travel around the entire globe in a day or so. Which, surely, makes containment incredibly problematic.
And it is almost inevitable that, sooner or later, another real "black death" will mutate and - with 21st Century communications - be dispersed at a speed previously unthought of.
In a way relatively "benign" epidemics perhaps offer almost a "dry run" for dealing with the logistics and consequences of dealing globally with a pandemic.