Today in History is a daily newsletter from Britannica. (more) Today in History—April 12: The Press Conference That Ended Polio Written by Michele Metych Michele Metych is the lead editor for Today in History at Encyclopædia Britannica. Michele Metych Fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Apr. 9, 2026 •History On this day in 1955, Thomas Francis, Jr., director of the Poliomyelitis Vaccine Evaluation Center at the University of Michigan School of Public Health, spoke to a packed auditorium—scientists, doctors, reporters—and distilled a 113-page report down to three important words: safe, effective, potent. Today in History is a daily newsletter from Britannica. Encyclopædia Britannica, Inc. Want to learn more about what happened on April 12, or any other day of the year? Sign up to receive the...

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