Viruses occur all the time and people die look up history of the earth and you will find out.
Do you mean we should literally look up "history of the earth"?? SMH. You'll need to refine your search terms, I think.
Then you'll need to find out what written records are available. But I will save you some time. Things like typhus were always around. But then came the Antonine Plague, which hit in about 165 CE It was probably smallpox. It killed enormous numbers of people. Some modern historians believe it was the start of the fall of the Roman Empire.
Don't ever make the mistake of imagining pandemics don't matter.