John Salamone and his wife believed they were "just doing the right thing" when they had their son David immunized with oral polio vaccine (OPV) six years ago.
But instead of being protected against the debilitating disease, the child developed vaccine-associated paralytic polio (VAPP).
Now 6, David's left leg is atrophied, but he recently started riding a bicycle.
"He's doing pretty well," John Salam-one said. "We count our blessings every day."