The history of pandemics is also the story of human beings' persistent fights against infectious diseases. Here are some of the worst pandemic examples in the past and how they ended.

The Plague of Justinian, caused by a single bacterium, spread across Europe, Asia, North Africa and Arabia, killing an estimated 30 to 50 million people, perhaps half of the world's population, in 541 AD.

According to a history professor at DePaul University, few understood how the plague ended eventually, the vast majority just somehow survived.

800 years later, the plague came back under the notorious name of "The Black Death." This time, it ruthlessly hit Europe, killing over 25 million people over the course of four years. Although people knew little about the disease, they sensed that it had something to do with proximity. So the Venetian officials made it mandatory to isolate the newly arrived sailors in a port city for 40 days before they were proven healthy. Historians said this might be the earliest version of quarantining, and it worked.

In the early 1500s, England, repeatedly hunted by the plague, imposed the law to isolate the sick, and marked out the house of the infected. When it came to 1655, the Great Plague killed 100,000 people in London in seven months. All public entertainment was banned, and people were asked to stay at home to avoid the mass spreading. As cruel as it sounds, this might be an effective way to put an end to this last plague.

Smallpox was endemic to Europe, Asia and Arabia for centuries, it killed three out of ten people after infection. But the death rate soared drastically when the virus arrived in countries like Mexico and the US in the 15th century.

A British doctor named Edward Jenner discovered in the late 18th century that milkmaids infected with a milder virus called cowpox appeared immune to smallpox. So he gave his gardener's 8-year-old son a cowpox vaccination before exposing him to the smallpox virus, and nothing happened.

The World Health Organization declared that smallpox had been eradicated from the planet in 1980, following widespread usage of the vaccination. It is the first and only disease to have been completely wiped off in human history.

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