All of Us Are Dead(2009)

Jigeum U-ri Hakgyoneun

Life at Hyosan High School is nothing special… until the students realize they’re in ground zero of a deadly virus that turns its victims into flesh-eating monsters. As the virus tears through their schoolmates in a matter of hours, they realize they have nowhere to run. Trapped in their high school with zombified versions of their friends and teachers, they must find a way to fight -- and escape with their lives.

(Source: WEBTOONS)