Dear Chris,
First of all, unless your practice is a medicare approved demonstration site, I wouldn't use this code for the drug.
In the facility where I work we have been instructed not to bill for the government provided drug or vaccine. The only code we add to the bill is for the administration of the drug or vaccine.
In my opinion, since Tamiflu is given within 48 hours of exposure to the flu, it would not be a vaccine, but rather a theraputic drug, and hence, I would use 96372, not 90471.
I hope this has been helpful.