Which disease is thought to have caused the most harm people?

Smallpox is considered to have caused the most harm to people over the centuries. It is estimated to have killed between 300 million and 500 million people in the 20th century alone, and it may have caused even more deaths in earlier times. Smallpox was a highly infectious disease that was characterized by a fever, rash, and pustules. It was often fatal, and even those who survived were often left with permanent scars. Smallpox was finally eradicated in the late 1970s thanks to a global vaccination campaign.