Until he was 4 months old, Braden Lerwick was a normal, healthy baby. But in the days and weeks after he got a routine vaccination, he began crying inconsolably, grew unresponsive and suffered seizures. Now age 10, he is profoundly handicapped, unable to speak or feed himself.

The likely cause: the diphtheria-tetanus-acellular pertussis, or DTaP, vaccine.