David contracted polio from the live polio vaccine when he was a baby. It was later discovered he had a serious underlying immune disorder, which meant he was susceptible to many infections, including polio.

TWiV 373: The distinguished virology career of Julius S. Youngner

"Vincent speaks with Julius about his long career in virology, including his crucial work as part of the team at the University of Pittsburgh that developed the Salk inactivated poliovirus vaccine."