According to the AAP (http://practice.aap.org/content.aspx?aid=1808
), 90471 - 90474 should be used. G0008 is only for Medicare as far as I know, but your 90471 shouldn't have denied, unless you tried to bill more than one 90471 on the claim, or if you also billed 90473. If either of those two situations is the case, then change the admin code to 90472, and you'll be good to go. If the flu vaccine was the only vaccine administered at the time, and you only reported 90471 once (with no 90473, either), then the denial is either a local coverage determination (Medicaid is weird like that - they just make up their own rules sometimes), or it was an incorrect denial, and just needs to be reprocessed. What did your denial say, when you billed 90471?