On the day in 1955 that Jonas Salk’s polio vaccine was pronounced “80 to 90 percent effective” against the form of the disease that caused paralysisph dream, 500 medical scientists and 150 reporters jammed into an auditorium at the University of Michigan for the announcement. Pots clanged, horns honked and factory whistles blew around the country.

Among national universities, Princeton was ranked No. 1 again, followed by the Massachusetts Institute of Technology and Harvard. Stanford, which tied for third last year, fell to No. 4. U.S. News again judged Williams College the best among national liberal arts colleges. Spelman College was declared the country’s top historically Black institution.

Calls for school crackdowns have mounted with reports of cyberbullying among adolescents and studies indicating that smartphones, which offer round-the-clock distraction and social media access, have hindered academic instruction and the mental health of children.

In the seven decades since, polio — a disease that once killed or paralyzed more than half a million people around the world each year — has been vanquished in the United States.

A lawyer advising Robert F. Kennedy Jr. has asked the Food and Drug Administration to revoke its approval of the current polio vaccine, a successor to the Salk vaccine, because it has not been tested against a placebo.

Experts say the move would be disastrous, because the polio virus is still around.

“We would have big outbreaks of polio,” warned Dr. Walter Orenstein, who ran immunization programs for the Centers for Disease Control and Prevention in the late 1980s and 1990s. Because some people infected with polio are asymptomatic, Dr. Orenstein said, the virus could spread through the population unnoticed — until people started getting paralyzed.

The Salk vaccine was tested against a placebo in 1.8 million American first- and second-grade schoolchildren in a so-called double-blind placebo-controlled trial — the gold standard in American medicine, in which half the study subjects get an inert vaccine and doctors, parents and patients did not know who got which.

Salk himself objected to the use of a placebo during the clinical trial; he couldn’t imagine depriving a child of a lifesaving vaccine. As the petition before the F.D.A. notes, the current vaccine, manufactured by Sanofi, was not tested against a placebo; scientists and doctors almost universally agree that withholding a lifesaving vaccine would be unethical.

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