ICD-10-CM > S00-T88 > T36-T50 > T50 > T50.A > T50.A1 > T50.A16 T50.A16 Underdosing of pertussis vaccine, including combinations with a pertussis component Non-Billable/Non-Specific Codes T50.A16A..., initial encounterT50.A16D..., subsequent encounterT50.A16S..., sequela