The Black Death probably falls into that category, being thought to have killed 30-60% of the population of Europe, and followed up by multiple subsequent related plagues over the ensuing centuries. The Plague of Justinian might have wiped out a similar proportion of the population a few hundred years before that.

Modern medicine and hygiene would have significantly increased survival rates, especially since many of the most deadly plagues are thought to have been bacterial and transmitted by flea bites. The other big difference is transport of course; historically extremely virulent and deadly diseases in many parts of the world had limited ability to spread beyond that particular ill-fated town or city, and rats and fleas were more necessary as well as more effective in helping the disease spread.