March of Dimes ran Salk's vaccine through a 1.8-million-child field trial

Every summer polio paralyzed thousands of American children, and Jonas Salk's inactivated vaccine promised to end the epidemics — but promise was not proof. Polio's attack rate is low, so a disease this rare needs enormous numbers before any protective effect is measurable at all, and no manufacturer's word would settle a question this charged.

The National Foundation for Infantile Paralysis — the March of Dimes — funded the answer: a two-year national clinical trial, run in 1954 across the country with over 1.8 million children, the largest clinical trial in history at the time. Evaluation was placed not with Salk's lab or a manufacturer but with Thomas Francis Jr.'s Poliomyelitis Vaccine Evaluation Center at the University of Michigan.

On April 12, 1955 Francis reported the vaccine safe and effective against paralytic polio — efficacy announced at roughly 90%, with trial-wide estimates putting protection near 70%. Millions worldwide rejoiced; US polio incidence fell from 13.9 cases per 100,000 in 1954 to under 0.5 per 100,000 by 1965.

Test once at national scale, under an independent judge

Scale solved the statistics: 1.8 million children produced enough paralytic cases in one season to answer a question a decade of small trials could not.

Independent evaluation at Michigan made the result credible to manufacturers, regulators and a nervous public simultaneously.

Charitable funding via the March of Dimes let the trial run on the scale the science required, not the scale a drug budget allowed.

A single decisive public verdict avoided years of partial adoptions, quiet failures and disputed anecdotes.

When a rare-outcome question must be answered now, buy certainty with scale: one independently judged trial settles what small studies never would. Fund the evaluation as seriously as the invention.

Within a decade US incidence had collapsed and endemic transmission ended in 1970, with the last domestically acquired case in 1979. The rush to vaccinate also produced the Cutter and Wyeth incidents — improperly inactivated lots that caused paralytic polio, sixty civil lawsuits and the Gottsdanker v. Cutter precedent for breach of product warranty, which hardened manufacturing oversight for every vaccine since. The Nobel committee declined to honor Salk, calling the work a technical achievement — the trial itself remains the template for population-scale vaccine evaluation.