I am an epidemiologist. I’ve been dealing with outbreaks of deadly pandemics my entire professional life.

Today, I want to share with you the story of how humankind has managed to defeat one of the most terrible diseases we’ve ever come into contact with.

Let me first introduce to you the variola major virus. Variola major causes smallpox. In the past, 3 out of 10 people who were unlucky to contract the virus, died. Variola major decimated mankind for centuries. But you haven’t heard about any cases of smallpox in recent years, have you? Why?

It’s because we eradicated smallpox. On May 8th 1980, the 33rd World Health Assembly declared the world free of the disease. The eradication of smallpox is considered to be, and rightly so, the biggest modern achievement in the area of public health. It is the result of many years of common effort of scientists, doctors, and ordinary citizens from all corners of the world. But let’s start from the beginning.

What is smallpox? It’s a highly infectious disease. The virus of smallpox is airborne, which means that it spreads quickly from person to person, travelling on droplets of mucus coming from the infected person’s mouth or nose. Even a few minutes in the presence of an infected person are likely to result in the virus jumping to a new host. Transmission of the virus is also possible through direct contact with an infected person or infected bodily fluids.

The first symptoms of smallpox resemble the flu or common cold, and most people will not experience any more serious stages of the disease. However, those that are less lucky will come out in a rash that will leave permanent scars on their bodies. Blisters with pus, or pustules appear both on the skin and inside the oral and nasal cavities.

This is why the most common complications of smallpox occur in the respiratory tract: patients often develop bronchitis or pneumonia.

How bad a disease is smallpox? Let me just give you one example. When in the 17th century the European settlers brought smallpox with them to North America, it reduced the native population of that continent by 90% within a year.

With the development of medicine, humanity discovered ways to control and prevent the transmission of various diseases. In the 18th century, Edward Jenner, an English doctor, came up with an idea of variolation. He used material from smallpox pustules, or rather, their powdered scabs, to make healthy people immune to smallpox. How? The powder was rubbed into tiny wounds made on the healthy person’s arm, or inhaled by the person. Jenner observed that the people who underwent the procedure developed smallpox‑like symptoms, but they rarely died. Yes, you’re thinking correctly: those were the humble beginnings of vaccinations!

In 1959, the WHO started planning a global campaign to free the world from the most horrible scourge of all times. The plan was simple: to vaccinate every single person on the Earth. But simple as it may have seemed, the plan soon turned out not to be feasible. The main obstacles, as you may guess, were the lack of money, shortages of personnel, and not enough commitment to the idea in some countries. Since viruses don’t respect administrative borders, even if one country managed to annihilate the virus, it came back there with just one infected person coming from a place where smallpox was still widespread.

Slowly, smallpox disappeared from North America, and soon after, from Europe. However, mainly due to reasons I have just mentioned, there were still outbreaks in South America, Asia, and Africa.

Therefore, the WHO decided to change its approach. The organisation gave up on the idea of vaccinating every single inhabitant of the globe, and focused instead on spotting the points where infections were found, isolating sick people, and vaccinating everyone within the 1.5 mile radius from the place where an infected person resided. And that worked!

The last known case of smallpox was recorded in 1977.

Does this mean that we will never ever have to worry about smallpox again? Hopefully. However, it has been decided that research on the smallpox virus should be continued just in case it resurfaces somewhere sometime, in a mutated and an even more morbid form. For that reason, samples of the variola virus are still stocked and studied in two laboratories: the Centers for Disease Control and Prevention in Atlanta, Georgia in the US and the State Research Center of Virology and Biotechnology in Koltsovo, Russia. The research done on the virus is aimed at developing better antiviral medication to treat patients affected by smallpox, and making safer and more effective vaccines. All research done on the variola virus is strictly supervised by the World Health Organisation.