Smallpox used to kill millions of people every year. Here’s how humans beat it.

“More than a million Americans have died of Covid-19, and the World Health Organization estimated this Thursday that the global death toll is around 15 million — a horrifying, and largely unnecessary, tragedy.

But for all that the world has lost in the last few years, the history of infectious disease has a grim message: It could have been even worse. That appalling death toll resulted even though the coronavirus kills only about 0.7 percent of the people it infects. Imagine instead that it killed 30 percent — and that it would take centuries, instead of months, to develop a vaccine against it. And imagine that instead of being deadliest in the elderly, it was deadliest for young children.

That’s smallpox.”

“Before modern vaccine development, humans had to get creative in slowing the spread of infectious disease. It was known that people who’d survived smallpox didn’t get sick again. In China, as early as the 15th century, healthy people deliberately breathed smallpox scabs through their noses and contracted a milder version of the disease. Between 0.5 percent and 2 percent died from such self-inoculation, but this represented a significant improvement on the 30 percent mortality rate of the disease itself.

In England, in 1796, doctor Edward Jenner demonstrated that contracting cowpox — a related but much milder virus — conferred immunity against smallpox, and shortly after that, immunization efforts began in earnest across Europe. By 1813, the US Congress passed legislation to ensure the availability of a smallpox vaccine that reduced smallpox outbreaks in the country throughout the 1800s.”

“By 1900, smallpox was no longer quite as much of a scourge in the world’s richest countries. In the 1800s, about 1 in 13 deaths in London were caused by smallpox; by 1900, smallpox caused only about 1 percent of deaths. Several countries in Northern Europe had also declared the disease eradicated. Over the next few decades, more of Europe, and then the US and Canada, joined them.

But as long as smallpox ravaged other parts of the globe, continual vaccination was necessary to make sure it wasn’t reintroduced, and millions of people continued to die of it. Data is spotty — this is before there was any international authority on infectious disease statistics worldwide — but it is estimated that 10 to 15 million people caught smallpox annually, with 5 million dying of it, during the first half of the 20th century.

It was not until the 1950s that a truly global eradication effort began to appear within reach, thanks to new postwar international institutions. The World Health Organization (WHO), founded in 1948, led the charge and provided a framework for countries that were not always on friendly terms to collaborate on global health efforts.”

“A 1947 outbreak in New York City, traced back to a traveler from Mexico, resulted in a frantic effort to vaccinate 6 million people in four weeks. Europe, Henderson says, repeatedly saw the virus reintroduced by travelers from Asia, with 23 distinct importations (different occasions of someone bringing smallpox into the country) in five years.

As we face down Covid-19, with effective vaccinations finally in hand, we’re encountering the same challenge that the world faced with smallpox in the 1950s: It doesn’t matter if a vaccine exists unless there also exists the international will and creativity to get it to all the people who need it, many of whom will be reluctant and skeptical.”

“features of smallpox made it easier to eradicate than many other diseases. For one thing, it didn’t have animal reservoirs; that is, unlike diseases like Ebola, smallpox doesn’t live in animal populations that can reintroduce the disease in humans. That meant that once it was destroyed in humans, it would be gone forever. And, once a person has survived it, they are immune for life. Only one vaccine is needed for immunity in almost all cases.

Additionally, it largely doesn’t have asymptomatic transmission and has a fairly long incubation period of about a week. That made it possible for public health officials to stay on top of the disease with a strategy of “ring vaccination” — whenever a case was reported, vaccinating every single person who may have come into contact with the affected person, and ideally everyone in the community could keep the disease at bay.”

“Humanity’s triumph over smallpox should stand out as one of our proudest moments. It called on scientists and researchers from around the world, including collaborations between rival countries in the middle of the Cold War.

Unfortunately, we’ve never replicated that success against another virus that affects humans. With some, such as polio, we’re drawing close. Wild polio has been eradicated in Africa and remains only in conflict-torn regions of Afghanistan and Pakistan. “Ring vaccination,” as practiced in the smallpox battle, has been successfully used in public health efforts against other diseases, most recently with the new Ebola vaccine, used against outbreaks in the Democratic Republic of Congo.

But in other cases, like HIV and Covid-19, we’ve let new diseases grow to pandemic proportions. And while those diseases have had devastating effects, it’s worth keeping in mind that they could have been even worse. Some viruses with the potential to escape laboratories or make the jump from animals to humans are as deadly and transmissible as smallpox, and Covid-19 has made it clear that we’re not prepared to handle them.”

“The devastation of Covid-19 has hopefully made us aware of the work public health experts and epidemiologists do, the crucial role of worldwide coordination and disease surveillance programs (which are still underfunded), and the horrors that diseases can wreak when we can’t control them.

We have to do better. The history of the fight against smallpox proves that we’re capable of it.”