The Spanish Flu

Around the time of WW1, a virus began to spread throughout the U.S., causing perfectly healthy soldiers to die of fluid in their lungs within days of falling ill (likely as a result of cytokinetic storms). It then traveled throughout Europe, ultimately killing 40 million people. The disease was similar to COVID-19, although much more deadly. The deadliness of the virus is attributed to its HA gene, which when swapped out reduced death rates in lab tests. Furthermore, there had been little knowledge of how to treat the disease, as it was originally thought to be a bacteria rather than a virus. There were no flu vaccines, no penicillin, and most physicians had left home and joined the war effort. Unwilling to let the pandemic lower morale, countries continued to fight, even as more soldiers died of H1N1 than of battle. Because Spain was one of the few countries to publicly report on the disease, it became associated with the flu (thus the name Spanish Flu). Hopefully, with the tools we currently have at our disposal, we can prevent COVID-19 from reaching the same levels as the 1918 pandemic.

https://www.cdc.gov/flu/pandemic-resources/reconstruction-1918-virus.html
https://virus.stanford.edu/uda/