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.