May 14, 1796 was a “golden day in the history of science”, says Derek Thompson in The Atlantic, “but a terrifying one for a certain eight-year-old boy”. Determined to prove that humans could be inoculated against smallpox by infecting them with cowpox, the British physician Edward Jenner slashed the arm of his gardener’s “brave and healthy son”, with a knife dipped in the ooze from a cowpox blister. After the boy recovered from a brief chill, Jenner stabbed him with a lancet infected with smallpox. “Nothing happened.” Jenner had invented a cure for “one of the deadliest viruses in world history”. The name he gave to this revolutionary new treatment, from the Latin for cow, was: “vaccine”.
Doctors still faced the “prodigious challenge” of delivering the stuff around the world, in an era before cold storage, planes or cars. Their solution was “ingenious”. In the early 1800s, two Spanish boys were given the smallpox vaccine just before they departed on a ship to the Americas. When they developed pustules, doctors scraped material from them and jabbed two other kids on board – and this “daisy-chain routine” continued until the ship reached modern-day Venezuela. From there, it travelled “arm-to-arm” to Mexico, Macau and Manila. Within 10 years, “the vaccine had gone global”.