Total deaths: About 200 million
In history: Since the late sixteenth century, there have been about a dozen full-fledged influenza pandemics, which occur when a new subtype of flu virus spreads rapidly and causes increased mortality. The pandemic of 1918–19, the most severe so far, killed at least 50 million and perhaps twice that many.
Current status: Due to the constant mutation of flu viruses, vaccines must be redeveloped annually and have a wide margin of error. In average years the seasonal flu is now responsible for between 290,000 and 650,000 deaths globally.
Total deaths: At least 200 million
In history: The early medieval Justinianic Plague killed as many as 50 million people, and the Black Death wiped out up to 60 percent of Europe’s population in the fourteenth century. In addition to these two pandemics, there have been centuries of localized outbreaks, with death tolls occasionally reaching a million.
Current status: Although it is now treatable with antibiotics, plague killed an average of ten people a year from 2010 to 2015, according to the WHO.
Total deaths: Up to 1 billion
In history: Evidence from Egyptian mummies suggests that smallpox may have begun infecting humans around 3000 bc. It caused about a tenth of all deaths in eighteenth-century Europe, by which time it may have killed up to 90 percent of the indigenous population of the Americas. Globally, 300 million people died in the first eight decades of the twentieth century alone.
Current status: While vaccines were developed around 1800, it took nearly two hundred years for the disease to be completely eradicated. Specimens of the virus are now known to exist only in two WHO-supervised laboratories, one in the United States and one in Russia.
Total deaths: More than 1 billion
In history: While many researchers believe tuberculosis emerged as a human pathogen early in prehistory, it was not a significant menace until the Industrial Revolution created ideal conditions for the disease to spread. Around a billion people are estimated to have died of it in the eighteenth and nineteenth centuries alone.
Current status: Drug-resistant strains began to evolve soon after the development of antibiotic treatments in the 1940s. The disease remains a leading cause of death globally, claiming 1.5 million lives in 2018.
Total deaths: Up to 5 billion
In history: Asked to comment upon a widely circulated claim that malaria has killed half of all humans who ever lived since it emerged in prehistory, epidemiologist Brian Faragher calculated that a more realistic estimate of the disease’s total death toll would be around 5 percent.
Current status: In 2018 about 405,000 people died of malaria worldwide. About two-thirds were children under the age of five.