Admin Code for Flue Vaccine and Injections

I have the following questions and looking for help.

Does some commercial insurance payers require Medicare (HCPCS) "G" (G0008-G0010) codes for admin? We know that CPT® codes (90471-90474 & 90460-90461) are required by the commercial payers. Are there any quidelines if some commercial payers are requiring "G" codes and who they are.


If the Provider is billing for injections such as J3420, J2900, J2001,
J1040 & J0696. For these injection what will be the administration codes?


For CPT® code 99406 do we have to always use 305.1 as primary ICD-9?

Thank you

Ray