I’m confused about the various vaccines that contain tetanus, diphtheria, and pertussis. Can you explain?

There are two basic products that can be used in children younger than age 7 years (DTaP and DT) and two that can be used in older children and adults (Td and Tdap). Some people get confused between DTaP and Tdap and others get confused between DT and Td. Here’s a hint to help you remember. The pediatric formulations usually have 3–5 times as much of the diphtheria component than what is in the adult formulation. This is indicated by an upper-case “D” for the pediatric formulation (i.e., DTaP, DT) and a lower case “d” for the adult formulation (Tdap, Td). The amount of tetanus toxoid in each of the products is equivalent, so it remains an upper-case “T.”