As discussed in Pediatric Coding Alert (Vol. 13, No. 3), you can bill multiple instances of +90472 (Immunization administration [includes percutaneous, intradermal, subcutaneous, or intramuscular injections]; each additional vaccine [single or combination vaccine/toxoid] [List separately in addition to code for primary procedure]). Just be sure to report 90471 for the first vaccine injection, then +90472 for each additional vaccine.