Reading about Science: The War on Smallpox

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In just the past few centuries, science has made great strides in the battle against infectious disease. Still, to date, smallpox is the only fully eradicated human disease. The only smallpox outbreaks identified since 1977 were the results of laboratory error. The elimination of smallpox is a huge success story for modern vaccination and international health organizations.


Smallpox is an infectious disease caused by the variola virus. It has been around for thousands of years (indeed, scientists believe that the Egyptian Pharaoh Ramses V died of it in 1157 BCE), and it has been estimated that smallpox claimed 300 million lives in the twentieth century alone.


Smallpox is transmitted through infected airborne droplets, typically because of sneezing or coughing. It has an incubation period of around ten to fourteen days, during which time the infected person exhibits no symptoms at all. Then, he or she endures two or three days of cold-like symptoms: chills, aches, and fever most commonly. Following this period, the victim quickly develops pustules all over his or her body. Approximately 30% of those afflicted died, and the rest were likely to have permanent scars. In all, it was a tremendously painful and devastating illness that showed no mercy to those who contracted it.


However, even long before a vaccine was developed, it was observed that those who had once suffered from and survived smallpox never got it again. From this observation, a practice known as variolation (or inoculation) emerged: this was the intentional transmission of small amounts of the virus. In its earliest days, variolation was quite primitive: people were injected with the fluid found in the pustules of victims, leading to milder infection and then immunity. This practice was somewhat effective but also a little risky, since the recipient would still be infected and contagious. Variolation was a step in the right direction, but it also contributed to the further spread of smallpox.


Ultimately, the world's first successful vaccine was developed by Edward Jenner (1749-1823). Jenner used cowpox, a milder illness, to create immunity in the recipient. Despite some initial push back against his novel methods, after a few decades there was widespread approval of the vaccine. The only obstacle that remained was the organizational task of delivering the vaccine worldwide.


The total eradication of smallpox had to wait until after World War II, with the establishment of the World Health Organization. The WHO introduced quality standards for vaccines, and in 1959 it announced a campaign to fully eliminate smallpox worldwide. The program had mixed results at first, as it was hampered by a lack of funding and by the rise in commercial air travel, which made it easier for smallpox to recirculate. However, progress continued slowly and steadily, and the final few outbreaks were managed with an innovative strategy called ring vaccination, in which health officials targeted all the people who had been in close contact with victims. By 1977, smallpox had been totally eradicated, and world health officials could confidently declare victory.


Source: Sophie Ochmann and Max Roser (2018) - "Smallpox". Published online at Retrieved from: '' [Online Resource]