It was one of the World Health Organization's (WHO) greatest triumphs: On May 8, 1980, the WHO declared the smallpox virus, "Variola," to be completely eradicated. In living memory, or as far as we know, the virus had killed many millions of people around the world and that over many centuries.

Alone in the 20th century, about 300 million people died because of smallpox.

But with an unprecedented, worldwide vaccination program, the WHO was able to put an end to the virus that had held humanity hostage for so long.  

Until then, an infection with an especially aggressive form of the smallpox virus, "Variola major," was often a death sentence — as many as 60% of patients died. And even those patients who contracted the less aggressive form, "Variola minor," tended to be marked by the disease for the rest of their lives.

Many patients lost their eyesight or hearing, some became paralyzed. Their entire bodies, including their faces, were covered with ugly scars left by the virus' characteristic, fluid-filled pustules. 

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Mass vaccination programs in rich, industrialized nations had worked well to limit the spread of smallpox. But those programs worked less well in poorer nations, such as India or in African countries, were health infrastructure was weak. Despite widespread vaccination campaigns, localized smallpox epidemics continued to break out regularly. And they often spread from there to larger areas. 

New vaccine strategy

In 1967, the WHO adopted a more flexible approach to vaccination programs. As the story of smallpox shows, the new strategy was so successful that it remains the standard today. It's allowed the WHO to react and adapt to local conditions.

And it's that flexibility that meant the smallpox vaccination program worked even in the most adverse scenarios, said Dr. Donald Henderson, who directed the WHO's global smallpox eradication program  between 1966 and 1977. 

"In 1960s and 70s, the program was beset by major floods, famines, civil war, hundreds of thousands of refugees in various parts of Africa and Asia and we did not have cell phones, we did not have email, we did not have fax machines, we didn't have Facebook, we didn't have Twitter, telex was possible on some occasions but too expensive," said Henderson before his death in 2016.

"I think it is a testimony to the skill and creativity of the international advisers from some 70 different countries as well as the ministers and health program staff who managed to overcome all of these [challenges] and achieve what had been deemed impossible," he said. 

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The vaccination strategy didn't only adjust to local conditions. Vaccination staff were able to target and reach individual patients in their specific environments. It was not without risk: The closer they got to infected patients, the higher the threat of contagion. But it was important to be able to vaccinate other people in a patient's social network.

As with the current coronavirus, SARS-CoV-2, smallpox is categorized as a "droplet infection" — it is transmitted from human to human via coughs and sneezes, for instance. But smallpox could also be transmitted via dust particles, such as by shaking out clothing or bed sheets that had been used by an infected person.      

Good preconditions

A few factors helped the ambitious smallpox eradication program.

First, the disease was easily diagnosed. Due to those characteristic pustules, which spread over a patient's entire body, infections were seldom overlooked or missed. That's not the case with the new coronavirus, where some infections can be asymptomatic. 

Second, infections often broken out in areas that could be clearly contained.

Third, the vaccine was sturdy and stable. It could be transported and administered in the most remote regions.

And fourth, the vaccine gave people a lifelong immunity. 

So, as soon as infections were reported, vaccine helpers were quickly deployed by the WHO to go to the specific region and vaccinate everyone in the vicinity of the infected person.

Dr. Margaret Chan, a former director general of the WHO, has said it was a huge logistical challenge.  

"Leadership at WHO was important, but an achievement of this scale ultimately depended on tens of thousands of dedicated workers who literally crisscrossed this entire globe, by jeep, donkey, and fishing boats, on foot in jungle and desert journeys, from nomadic tribes in remote mountain areas to permanent dwellers in the scorching heat of Asia's slums," said Chan. 

They vaccinated both those people who had had contact with the patient but also those people with whom those people had had contact as well. Using this quasi snowball system, the teams were able to create what's called "ring vaccination" around the infected person or people. 

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It was a process of elimination that saw about 2.4 billion vaccinations administered worldwide. It cost $300 million (€278 million) and the work of 200,000 helpers. 

But it was worth it. The new strategy proved to be very effective. Since the last-recorded case in 1977 in Somalia, smallpox is not known to have returned.  

Fear of biological weapons attacks

The smallpox vaccine is, however, known to have certain — some dangerous — side-effects. Perhaps as a result, compulsory smallpox vaccination was stopped in many places once the virus was deemed eradicated.

There are now only two locations where, officially, samples of the smallpox virus are held — one is a Russian research laboratory called VECTOR, southeast of Novosibirsk, and the other is an American research center, run by the U.S. Centers for Disease Control and Prevention (CDC), in Atlanta. 

Read more: Russia says no danger after blast in smallpox lab

But it is possible that other states are holding samples of the deadly virus, secretly.

After the 2001 terrorist attacks in the U.S., the potential for a biological weapons attack was hotly discussed. It was felt that without the once-compulsory vaccine, many people would have no protection against a smallpox epidemic.

That's one reason why those samples in the U.S. and Russia are being maintained. Without them, it would be impossible to test the effectiveness of any new vaccine.

As a result, many nations have stockpiled doses of the smallpox vaccine. The U.S., for instance, has about 100 million doses. Germany, Great Britain, Israel and South Africa also hold large quantities of the vaccine. 

The WHO has 64 million doses of the costly vaccine. But even that wouldn't help to protect an entire population if a serious epidemic broke out in a developing nation. A new smallpox epidemic would have no trouble spreading quickly, far and wide. 

Success as a spur

The successful eradication of smallpox is a unique story in the history of medicine. But it is keenly read as an incentive to eradicate other infectious diseases. 

Donald Henderson once described the eradication of smallpox as a historic milestone and "one of the most brilliant accomplishments in medical history." But he also said that "smallpox eradication was not an end in itself."

"In 1974, the [WHO] Assembly agreed to set in motion an expanded program on immunization whose goal was to ensure that the world's children would also be protected against measles, polio, diphtheria, pertussis (whooping cough) and tetanus," Henderson said. "The 80% mark was reached in 1990, and with this a new era has emerged for public health achievement through vaccination."

But the weight of expectation on the WHO, not least in light of the current coronavirus pandemic, has grown since Henderson spoke those words. 

The hope is that the WHO can adopt a similar role now to coordinate an international campaign against SARS-CoV-2, so that a vaccine can be quickly developed and that it is affordable enough to help the entire world population.  

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