A strain of bird flu known as H5N1 or highly pathogenic avian influenza has made a worrying leap to cattle herds across the US over the past month. This development has sparked “enormous concern” among health experts, including the World Health Organization’s (WHO) chief scientist, who warned of the virus’ “extremely high” mortality rate in humans.
I dunno about 50%, but Native Americans had a >90% mortality from European disease at the time of the Columbian Exchange, and it messed them up pretty badly.
The Black Death killed maybe 50% of Europe’s population.
https://en.wikipedia.org/wiki/Black_Death
That didn’t end European civilization, but it was a cataclysmic event, left huge scars.
Though they also had shorter supply chains and such, were maybe more-resilient to disruption.
It’s a matter of being different societies, occurring over different lengths of time, and being global instead of regional.