Factors associated with influenza vaccination in middle and older aged Australian adults according to eligibility for the national vaccination program

Background: In Australia, influenza vaccination is recommended and provided free of charge for all adults aged ≥65 years and those aged <65 years with specific risk factors. Other than age, there is limited information on characteristics associated with vaccine uptake. 

Methods: We used the 45 and Up Study, a large cohort of adults aged ≥45 years, who completed a questionnaire in 2012 asking about influenza vaccination. We compared characteristics of those reporting influenza vaccination in those aged <65 and ≥65 years using a log binomial model to estimate relative rates (RRs), adjusted for age and other factors. 

Results: Among 27,036 participants, the proportion reporting influenza vaccination in the last year increased steadily with age from 24.6% in those <54 years to 67.2% in those 75-79 years; of those eligible for universal free vaccine, (≥65 years) 57.3% had an influenza vaccination in the previous year. Many characteristics associated with higher vaccination rates in adults aged <65 years (mean 60.7) and those ≥65 years (mean 73.7) were similar. These included sex (women versus men: <65 years, aRR=1.14[95% CI 1.08-1.20]; ≥65 years, aRR=1.04[1.02-1.07]), higher BMI (≥30kg/m² versus >18.5 to <25kg/m²: <65 years, aRR=1.16[1.09-1.24]; ≥65 years, aRR=1.06[1.03-1.09]), requiring assistance with daily tasks versus not (<65 years, aRR=1.27[1.15-1.40]; ≥65 years, aRR=1.05[1.02-1.09]) and reporting versus not reporting specific chronic illnesses (<65 years, aRR=1.55 [1.48-1.63]; ≥65 years, aRR=1.08[1.06-1.10]). Current smokers had lower vaccination rates (<65 years, aRR=0.78[0.69-0.90]; ≥65 years, aRR=0.91[0.84-0.99]). Among those aged <65 years only, being a carer, higher income, and education were associated with influenza vaccination (aRR=1.32[1.19-1.47], 1.17[1.10-1.24] and 1.12[1.10-1.22] respectively). Non-English speaking country of birth was associated with lower vaccination rates in ≥65 years (aRR 0.86[0.81-0.92]). 

Conclusions: Factors most strongly associated with vaccination were age and among those aged <65 years, having a medical indication recommended for influenza vaccination, suggesting higher uptake among those who can access free vaccine. Among those eligible for free vaccination, interventions could be targeted towards men, smokers, those from non-English speaking backgrounds and those <65 years with a medical indication.