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Polio vaccines (Salk, Sabin)
1955 (Salk); 1961 (Sabin oral)· Invention or discovery· Germs, drugs & genetics
Well documentedSolid records, physical evidence or scientific consensus.
Jonas Salk's injected vaccine (1955) and Albert Sabin's oral vaccine (1961) protected against polio, a virus that paralyzed children.
See it on the Technology & Medicine map →How it works
Polio spreads through contaminated water and hands; in a small share of cases it attacks nerves and causes paralysis. US epidemics peaked in 1952 with about 58,000 cases. Salk's vaccine used killed virus; a 1954 field trial of about 1.8 million children, run by Thomas Francis, proved it worked, announced April 12, 1955. Sabin's weakened live-virus drops were cheaper and easier to give. John Enders's team made both possible by growing poliovirus in lab cultures (1949).
Why it mattered
Wild polio cases have fallen over 99% worldwide since 1988, and the wild virus now survives only in Pakistan and Afghanistan.
How we know
The 1955 Francis report on the field trial, US disease records, and case counts kept by the Global Polio Eradication Initiative since 1988.
Still unknown or debated
Whether eradication can be finished: rare outbreaks of vaccine-derived polio, from weakened virus in the oral drops, complicate the endgame.
Connections (3)
▸James Lind's scurvy trial pioneered the controlled trial used for Polio vaccines (Salk, Sabin)Mostly agreed
The connection
Lind's 1747 trial gave groups of sick sailors different treatments side by side, so results could be compared fairly. The 1954 Salk field trial applied that logic at huge scale: many children got either vaccine or a look-alike placebo, with neither families nor doctors knowing which, and cases were counted afterward.
When and how
HMS Salisbury, 1747; the 1954 Francis Field Trial in the US, Canada and Finland, run from the University of Michigan by Thomas Francis Jr.
How sure are we?
The method's lineage is clear in medical history, though the polio trial's designers drew more on 20th-century statistics, such as Ronald Fisher's randomization, than on Lind directly.
Debates and open questions
Historians question calling Lind the inventor of trials: he tested only 12 men, and earlier comparisons exist. The polio trial's design itself was hotly argued in 1954.
▸Vaccination (Jenner's smallpox vaccine) was extended to Polio vaccines (Salk, Sabin)Well documented
The connection
Jenner showed in 1796 that a mild related infection, cowpox, could train the body to resist smallpox. Pasteur generalized the idea in the 1880s with weakened germs. Salk's killed-virus shot and Sabin's weakened live-virus drops applied the same principle to polio, once scientists could grow the virus in lab cultures.
When and how
Berkeley, England, 1796 (Jenner); Pasteur's lab in Paris, 1879–85; Pittsburgh (Salk) and Cincinnati (Sabin), 1950s.
How we know
The line of descent is documented in the scientists' own papers; Pasteur proposed extending the word 'vaccine', from Latin vacca (cow), to all such shots in Jenner's honor.
Debates and open questions
Smallpox fell to one vaccine partly because it showed obvious symptoms; polio has three types and spreads silently, one reason its eradication is still unfinished.
▸Smallpox eradication inspired a global eradication drive using Polio vaccines (Salk, Sabin)Well documented
The connection
Smallpox's defeat showed a disease could be wiped out worldwide. In 1988 the World Health Assembly launched the Global Polio Eradication Initiative, using the oral Sabin and injected Salk vaccines. Cases have fallen by over 99 percent from an estimated 350,000 in 1988, and wild polio now survives only in Pakistan and Afghanistan.
When and how
The World Health Assembly in Geneva, May 1988, with Rotary International, UNICEF and the US CDC; Rotary had begun its PolioPlus campaign in 1985.
How we know
The 1988 resolution cites smallpox's success, and smallpox veterans such as Ciro de Quadros went on to lead polio campaigns in the Americas.
Debates and open questions
Polio is harder: most infections show no symptoms, and the oral vaccine can rarely mutate and spread. Even D. A. Henderson doubted full eradication was achievable.