Medicare Benefits Schedule data to monitor influenza immunisation in Australian adults

Introduction: In Australia, adult immunisation coverage is primarily monitored via periodic telephone surveys that rely on self-reported immunisation status. All Australian residents are eligible for Medicare, so we examined the feasibility of using immunisation-specific Medicare Benefits Schedule (MBS) item numbers to monitor and estimate adult influenza immunisation coverage. Methods: Baseline questionnaire data from 267 129 participants from the 45 and Up Study, a prospective cohort study, were linked to data containing information on individual MBS immunisation-specific items from 2006 to 2011. Temporal trends in recording of these items were examined. Self-reported influenza immunisation status obtained from a follow-up questionnaire from 27 036 participants was then compared with the MBS immunisation records. Results: From 2006 to 2011, the pattern of MBS immunisation claims was consistent with self-reported influenza immunisation trends, with annual peaks occurring from March to May. There was fair agreement between MBS immunisation records and self-reported influenza immunisation: 48.8% (95% CI 47.1, 50.4) of participants who self-reported influenza immunisation had a matching MBS record, and 79.6% (95% CI 78.8, 80.4) who reported never having influenza immunisation had no matching MBS record. However, compared with self-reported influenza vaccination for people aged ≥65 years from the 2009 Adult Immunisation Telephone Survey (74.6%), the proportion of participants aged >65 years with an MBS immunisation record was low, with an annual median of 39.3% (range 28.3-62.1%). Conclusion: MBS immunisation item data are readily available and may be useful to monitor trends in adult influenza immunisation, but they are likely to substantially underestimate coverage. Other approaches, such as capture of general practitioner-delivered influenza vaccine doses or a whole-oflife immunisation register, are needed to comprehensively monitor and estimate adult immunisation coverage for influenza and other recommended adult vaccines.