Both CPT® and CMS (Medicare) has made it clear that it is not appropriate to report a nurse visit when giving a flu shot.  That is: do not bill a nurse visit when the patient presents to the office for a flu shot.  Bill only for the administration of the vaccine and for the serum, if the practice purchased the serum.

This is the same principle as billing for a nurse visit in place of another service, or in addition to another service.  It is not correct to bill for a nurse visit when the patient presents for blood drawing, when the only service is venipuncture and processing of the specimen. 

See the article in Codapedia on nurse visits for more information.