The impact of non-financial and financial encouragements on participation in non school-based human papillomavirus vaccination: a retrospective cohort study

Objective Adolescent vaccination coverage under a system of non school-based vaccination is likely to be suboptimal, but might be increased by targeted encouragement campaigns. We analysed the effect on human papillomavirus (HPV) vaccination initiation by girls aged 1218 of two campaigns set up in Flanders (Belgium) in 2007 and 2009: a personal information campaign and a combined personal information and financial incentive campaign. Methods We analysed (objective) data on HPV vaccination behaviour from the National Alliance of Christian Mutualities (NACM), Flanders largest sickness fund. We used z-scores to compare the monthly proportion of girls initiating HPV vaccination over time between carefully selected intervention and control groups. Separate analyses were done for older and younger girls. Total sample sizes of the intervention (control) groups were 221 (243) for the personal information campaign and 629 (5,322) for the combined personal information and financial incentive campaign. Results The personal information campaign significantly increased vaccination initiation, with older girls reacting faster. One year after the campaign the percentages of vaccination initiation for the oldest girls were 64.6 and 42.8 % in the intervention and control group, respectively (z = 3.35, p = 0.0008); for the youngest girls the percentages were 78.4 and 68.1 % (z = 1.71, p = 0.09). The combined personal information and financial incentive campaign increased vaccination initiation among certain age groups. One year after the campaign the difference in percentage points for HPV vaccination initiation between intervention and control groups varied between 18.5 % (z = 3.65, p = 0.0002) and 5.1 % (z = 1.12, p = 0.26). Conclusion Under a non school-based vaccination system, personal information and removing out-of-pocket costs had a significant positive effect on HPV vaccination initiation, although the effect substantially varied in magnitude. Overall, the obtained vaccination rates remained far below those realised under school-based HPV vaccination.