denial for not using a base code?

cpt code 90472 with icd-9 code v05.3.
Pt has 2 vaccines on visit. what are they meaning by a base code?

add-on code

To report the first immunization given during a single patient encounter, report code 90471. Code 90472 is considered an "add-on" code (hence the "+" symbol next to it) to code 90471. This means that the provider will report 90472 in addition to 90471 if more than one vaccine is administered during a single patient encounter. You cannot report code 90472 without its base code 90471.