I just found this little gem of a killer on WIKI
https://www.history.com/topics/middle-ages/black-death
It's old stuff though. Thought you might enjoy this bit
The Black Death was a devastating global epidemic of bubonic plague that struck Europe and Asia in the mid-1300s. The plague arrived in Europe in October 1347, when 12 ships from the Black Sea docked at the Sicilian port of Messina. People gathered on the docks were met with a horrifying surprise: Most sailors aboard the ships were dead, and those still alive were gravely ill and covered in black boils that oozed blood and pus. Sicilian authorities hastily ordered the fleet of “death ships” out of the harbor, but it was too late: Over the next five years, the Black Death would kill more than 20 million people in Europe—almost one-third of the continent’s population.
Wowser
Here are a couple more:
430 B.C.: Athens
The earliest recorded pandemic happened during the Peloponnesian War. After the disease passed through Libya, Ethiopia and Egypt, it crossed the Athenian walls as the Spartans laid siege. As much as two-thirds of the population died.
The symptoms included fever, thirst, bloody throat and tongue, red skin and lesions. The disease, suspected to have been typhoid fever, weakened the Athenians significantly and was a significant factor in their defeat by the Spartans.
This one was a Doozy
541 A.D.: Justinian Plague
First appearing in Egypt, the Justinian plague spread through Palestine and the Byzantine Empire, and then throughout the Mediterranean.
The plague changed the course of the empire, squelching Emperor Justinian's plans to bring the Roman Empire back together and causing massive economic struggle. It is also credited with creating an apocalyptic atmosphere that spurred the rapid spread of Christianity.
Recurrences over the next two centuries eventually killed about 50 million people, 26 percent of the world population. It is believed to be the first significant appearance of the bubonic plague, which features enlarged lymphatic gland and is carried by rats and spread by fleas.
Rats and Fleas.. interesting. Are you itchy tonight?? 
And of course, CO 19 and I read now that maybe 2.6 million (1.6 million as of Dec 2020) have died from it. Apparently masks are a good thing. That would be about one 2500th of the world's population, or .04 percent. Just looking at other percentile figures and that suggests to me that this thing is nothing like the bad ones that killed over 10% and even that figure is roughly 2500 times as bad as this 'Monster' and I have often said this thing is a bad one, but is also over hyped
SOURCES
Disease and History by Frederick C. Cartwright, published by Sutton Publishing, 2014.
Disease: The Story of Disease and Mankind's Continuing Struggle Against It by Mary Dobson, published by Quercus, 2007.
Encyclopedia of Pestilence, Pandemics, and Plagues by Ed, Joseph P. Byrne, published by Greenwood Press, 2008.
Influenza, The American Experience.
Source Book of Medical History, Logan Clendening, published by Dover Publications, 1960.