Worst Pandemics in History and How they ended?

Docsun Clinical AI Laboratory
6 min readOct 25, 2020


As the world comes to terms with the COVID-19 pandemic caused by the Coronavirus, one might find some morbid comfort in considering the historical context of global pandemics that are now the things of the past. The mortality rate estimate of the current pandemic can only be preliminary until mass testing is done and the final numbers come in. That said, the Director of the NIH National Institute of Allergy and Infectious Diseases, Dr. Anthony Fauci, and others prominent in the field of epidemiology have estimated that Covid-19’s mortality rate will be around 1%, which is 10 times higher than an average seasonal flu.

Image Source: The Conversation

The mortality rates for past pandemics have been far higher. Middle Ages Europe’s 14th-century plague is estimated to have killed between 30% and 60% of the population. Old-world diseases in which Europeans had developed resistance and immunity to are estimated to have killed between 25% to 50% of many Native American tribes in post-Columbian 16th-century North America.

The Centers for Disease Control and Prevention (CDC) defines an epidemic as being when there’s an increase –often suddenly– in the number of cases of an infectious disease above what is normally expected in a localized population. It defines a pandemic as an epidemic that has spread over several countries or even continents. Pandemics usually affect large segments of the population.

We’ve all lived through first-hand what it’s like to experience a pandemic with an estimated 1% mortality rate. Just imagine living through exponentially worse, without the benefit of modern medicine and healthcare.

Smallpox Pandemic, 1877–1977

  • Estimated 500 million killed
  • Caused by two smallpox viruses
  • Spread primarily by touching an infected object or person
  • Mortality rate: up to 35%

In 1980 the World Health Organization (WHO) declared smallpox to be eradicated. Prior to that the small sores that would form over the entire body, fill with fluid, scab off, and cause scarring, blindness, and death were a very unfortunate fact of life for many. It was so widespread and so deadly that the first-ever vaccine developed in the world was for smallpox. Before proper vaccines were invented, one method of developing immunity was to take dried pox scabs from a person who’d died, dry and crush them up, and then snort them. The mortality rate for this treatment was in the ballpark range of what Covid-19’s is today: 0.5%-2.0.

Black Death Plague, 1347–1351

  • 75 to 200 million estimated killed
  • Caused by the bubonic plague bacteria
  • Spread by infected fleas and perhaps body lice
  • Mortality rate: 10% with treatment, up to 90% without

Up to 200 million people killed is a big deal no matter how you look at it. In the 14th century, the world’s population was estimated to be 443 million. That means the Black Death killed between 17% and 45% of the entire global population. Modern understanding of the bubonic plague bacteria posited that an increase in Europe’s rat populations meant more fleas. Fleas would bite a rat infected with the plague bacteria, and then infect healthy people when they would bite them next. A 2018 study introduced new evidence to support a human-flea-human transmission model, taking the blame off rats, and even suggesting that human body lice could have been one of the primary vectors.

Spanish Flu Pandemic, 1918–1919

  • 17 to 100 million estimated killed
  • Caused by the H1N1 influenza A virus
  • Airborne transmission from coughing, sneezing, and breathing
  • Mortality rate: 2.5%

Between the spring of 1918 and the summer of 1919, approximately 500 million people caught the Spanish Flu, around one-third of the world’s total population. Its spread was helped by modern advancements in transportation and troop movements during World War One. Spain was neutral in that war, which meant newspapers weren’t censored to the extent they were in Allied and Central countries. When the Spanish king became gravely ill with the virus the country became the focal point for reporting and eventually even lent its name to that particular H1N1 strain. Theories about the virus’ true country of origin include France, England, China, and the United States. Researchers believe the virus originated in birds, and either jumped to humans directly or used pigs as an intermediary before jumping to humans.

HIV/AIDS Pandemic, 1981-present

  • Approximately 32 million estimated killed
  • Caused by the Human Immunodeficiency Virus (HIV)
  • Transmitted through contact with the blood, semen, or breast milk of an infected person
  • Mortality rate: has varied over time from being very high to manageable today, though there are stark differences between the developed and developing world

Since its clinical discovery in 1981, HIV/AIDS has killed around 865,000 people on average each year. Today in the United States there are about 1.1 million people living with HIV/AIDS, and an estimated 38,000 new infections occur every year. In 2018 17,032 people were in the last stage of the virus where the body’s immune system is badly damaged. HIV/AIDS used to be viewed as an inevitable death sentence, however today with proper treatment in the developed world many views it more as a life-threatening chronic illness. It’s another story in the developing world, where HIV/AIDS is the fourth-leading cause of death, accounting for approximately one fatality for every 2,222 people. Despite extensive research medical experts have yet to come up with a vaccine.

Plague of Justinian, 541–542

  • Killed between 25 and 100 million
  • Caused by the bubonic plague bacteria
  • Spread by infected fleas and perhaps body lice
  • Mortality rate: 10% with treatment, up to 90% without

Once again tens-of-millions dead is a huge amount in itself and gets even bigger when it’s put into the context of a global population that numbered 198 million in the 6th century. That means between 13% and 51% of the world’s population fell victim to the Plague of Justinian, with multiple resurgences taking place for two centuries afterward until it would go back to relative dormancy. Some historians speculate that this outbreak may have been the straw that broke the camel’s back to usher in the Dark Ages. On the bright side others point out it could have been the harbinger of the end of slavery in the Byzantine Empire, as the shortage of laborers meant they could leverage their work for freedom.

Third Plague Pandemic, 1855–1960

  • Over 15 million killed
  • Caused by the bubonic plague bacteria
  • Spread by infected fleas and perhaps body lice
  • Mortality rate: 10% with treatment, up to 90% without

Not to be outdone by other pandemics, the plague would rear its ugly head again between the 19th and 20th centuries, this time originating in Yunnan, China. It spread along with tin and opium trade routes, making its way westward through India –most victims were in China and India– and eventually even reaching the United States. The bubonic plague bacteria survive to this day among wild rodents in some parts of the Southwestern United States. Since the year 2000, 12 people have died, and about seven new cases are diagnosed on average each year. It’s thought that the Third Plague Pandemic is responsible for introducing the plague into the natural environment after flea-infested rats stowed passage on ships across the Pacific from China.

Hong Kong Flu, 1968–1970

  • At least 1 million killed
  • Caused by the H3N2 strain of the influenza A virus
  • Airborne transmission from coughing, sneezing, and breathing
  • Mortality rate: between 0.1% and 0.5%

The first recorded case of this influenza virus was reported in Hong Kong, though it could have originated in mainland China. It would go on to infect around half-a-million Hongkongers, approximately 1.5 out of every 10 people. It spread at first throughout Asia and then became a true pandemic, reaching the rest of the world. One-tenth of the total worldwide deaths occurred in the United States where 100,000 perished. As with the Spanish Flu, researchers believe this flu strain originated in birds and made the leap to humans either directly or with pigs or possibly other animals serving as intermediaries.

Other flu pandemics have wreaked havoc throughout the world’s population, with notable outbreaks in 1889–1890 and 1957–1958, and each claimed over 1 million victims.

Source: Public Health Online



Docsun Clinical AI Laboratory

Docsun Clinical AI Laboratory is a social initiative working on Artificial Intelligence powered Covid-19 Rapid Testing technology.