Go look up how people reacted to the Spanish flu. Or various religious death cults that pop up with regularity.

This isn’t a modern thing - most people rely on their social network about what is true and those social networks can be infected with cultural disease and rot and die just like the body. The problem is that cultural diseases have impacts to the entire species since we’re social creatures and technology has further shrunk the distance between cultures and the time disease takes to spread making it difficult to contain.