By SAM ROBERTS

Julius Youngner, an inventive virologist whose nearly fatal childhood illness destined him to become a medical researcher and a core member of the team that developed the Salk polio vaccine in 1955, died on April 27 at his home in Pittsburgh. He was 96.

His death was confirmed by his son, Dr. Stuart Youngner.

Dr. Youngner was the last surviving member of the original three-man research team assembled by Dr. Jonas Salk at the University of Pittsburgh to address the polio scourge, which peaked in the United States in the early 1950s when more than 50,000 children were struck by it in one year. Three other assistants later joined the group.

Dr. Salk credited his six aides with major roles in developing the polio vaccine, a landmark advance in modern medicine, which he announced on April 12, 1955.

The announcement — that the vaccine had proved up to 90 percent effective in tests on 440,000 youngsters in 44 states — was greeted with ringing churchbells and openings of public swimming pools, which had been drained for fear of contagion. Within six years, annual cases of the paralyzing disease had declined from 14,000 to fewer than 1,000.

By 1979, polio had been virtually eliminated in developed nations.

“I think it’s absolutely fair to say that had it not been for Dr. Youngner, the polio vaccine would not have come into existence,” Dr. Salk’s son, Peter L. Salk, president of the Jonas Salk Legacy Foundation and a visiting professor at the University of Pittsburgh Graduate School of Public Health, said in an email.

While Dr. Youngner, who was 34 at the time, remained at the university and made further advances in virology, he and other members of the team remained embittered that Dr. Salk had not singled them out for credit in his announcement speech.

The printed version was prefaced with the phrase “From the Staff of the Virus Research Laboratory by Jonas E. Salk, M.D.,” and a United Press account quoted him as crediting his original three assistants, who had joined him as early as 1949 — Dr. Youngner, Army Maj. Byron L. Bennett and Dr. L. James Lewis — as well as three others.

“The really important thing to recognize is that the development of the polio vaccine at the University of Pittsburgh was a team effort,” Dr. Peter Salk wrote.

He added, “There is no question that my father recognized the importance of the team, and if there were circumstances in which that wasn’t adequately expressed, I would feel that it needs to be expressed now and very clearly so.”

In 1993, Dr. Youngner crossed paths with Dr. Salk for the first time since Dr. Salk left for California in 1961. According to “Polio: An American Story” (2005), by David M. Oshinsky, Dr. Youngner raised the 1955 announcement speech in confronting Dr. Salk.

“Do you remember whom you mentioned and whom you left out?” the book quoted him as saying to Dr. Salk. “Do you realize how devastated we were at that moment and ever afterward when you persisted in making your co-workers invisible?”

Asked later, though, whether he regretted having worked for Dr. Salk, Dr. Youngner replied: “Absolutely not. You can’t imagine what a thrill that gave me. My only regret is that he disappointed me.”

Dr. Youngner’s contribution to the team was threefold.

He developed a method called trypsinization, using monkey kidney cells to generate sufficient quantities of the virus for experiments and production of the vaccine. He also found a way to deactivate the virus without disrupting its ability to produce antibodies. And he created a color test to measure polio antibodies in the blood to determine whether the vaccine was working.

He later contributed research to understanding interferon as an antiviral agent in the treatment of cancer and hepatitis; to the development (with Dr. Samuel Salvin) of gamma interferon, which is used against certain infections; and to advances that resulted in vaccines for Type A influenza and (with Dr. Patricia Dowling) equine influenza.

“As a direct result of his efforts, there are countless numbers of people living longer and healthier lives,” Dr. Arthur S. Levine, the University of Pittsburgh’s senior vice chancellor for the health sciences and dean of its medical school, said in a statement.

Julius Stuart Youngner was born on Oct. 24, 1920, in Manhattan and raised in the Bronx, where he survived lobar pneumonia, a severe infection of the lungs. His father, Sidney Donheiser, was a businessman. His mother was Bertha Youngner. He took her surname when his parents divorced.

After graduating from Evander Childs High School in the Bronx at 15, he earned a bachelor’s degree in English with a minor in biology from New York University in 1939 and a master’s and doctorate of science in microbiology from the University of Michigan.

Drafted into the Army in World War II, he worked on the Manhattan Project at Oak Ridge, Tenn., and at the University of Rochester, testing the toxicity of uranium salts. He said he learned of the project’s goal of building an atomic bomb only when it was dropped on Japan.

He was working at the National Cancer Institute, part of the National Institutes of Health, when the University of Pittsburgh hired him as an assistant professor in 1949 to assist Dr. Salk. He was a professor of microbiology and medical genetics at the university School of Medicine and chairman of the department of microbiology (biochemistry and microbiology were added later) from 1966 until his retirement in 1989.

His first wife, the former Tula Liakakis, died in 1963. Besides their son, Stuart, a psychiatry and bioethics professor at Case Western Reserve University in Cleveland, Dr. Youngner is survived by his wife, the former Rina Balter; a daughter, Lisa, an artist, also from his first marriage; three grandchildren; and a half brother, Alan Donheiser.

Dr. Youngner’s infectious curiosity, as a colleague characterized it, generated hundreds of scholarly papers and more than 15 patents. He was president of the American Society for Virology from 1986 to 1987.

When he was 7, Dr. Youngner nearly died from the pneumonia he had contracted when bacteria ate through his chest and infected a rib. An effective vaccine for pneumonia and antibiotics would not be invented for nearly two decades.

“So they strapped my legs to a table, and two nuns held my arms and another held my head and they prayed while they operated on me,” he recalled in an oral history interview in the early 1990s with the National Council of Jewish Women. “To this day I can remember the feeling of the saw on that rib.

“Later in life, when I had to have some minor surgery,” he said, “I put it off for years because I was so affected by this episode.”