But his most noteworthy innovation — developing the first viable vaccine against polio and testing it successfully on humans — is far less well known. It has long been eclipsed in public memory by the triumphs of Salk, whose injectable vaccine was introduced in 1955, and Sabin, whose oral vaccine was introduced in stages in the early 1960s.

“Koprowski’s was the first serious scientific attempt at a live-virus polio vaccine,” said the historian David M. Oshinsky, whose 2005 book, “Polio: An American Story,” chronicles the race to pre-empt the disease. “Jonas Salk is a god in America, Albert Sabin’s got a ton of publicity, and Hilary Koprowski, who really should be part of that trinity, is the forgotten man.”

From the beginning, a live-virus vaccine like Dr. Koprowski’s was the most coveted weapon in the war on polio. Such vaccines can be administered orally and are far cheaper than injections. And because they involve live viruses, which can spread within a community, they can also confer immunity on others. (The Salk vaccine, made from killed viruses, cannot.)

But there was a grave catch: for a live polio vaccine to be safe, the viruses would have to be sufficiently weakened — attenuated, in medical parlance — so they would produce antibodies without inducing polio’s neurological effects.

On the evidence, the Koprowski vaccine did precisely this. But though it was given to patients overseas with good results, it was never approved for use in the United States.