ICD-10 vaccine coding

I know ICD-10 provides one code for encounters for immunizations, Z23, but there is a note to code first any routine childhood examination. I also find on the encoder we use a note indicating Z23 is not an acceptable primary dx. So, my question relates to coding vaccines for older patients, specifically Medicare patients. Can we assign Z23 as a solo dx on a flu or pneumonia vaccine? ICD-10 doesn't provide other codes to describe the type of vaccine given, the CPT® description will cover that. I can't find any guidance on this anywhere and would appreciate other thoughts.