The effect of pre-booked appointments on COVID-19 vaccine uptake among previously vaccinated older adults during the 2023 autumn campaign in the Netherlands: a regression discontinuity analysis

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INTRODUCTION: There is evidence that pre-booked appointments (PBA) for vaccination can enhance uptake, but might also result in reactance. We assessed the effect of PBA versus self-scheduling on uptake of COVID-19 vaccination during the 2023 autumn campaign in the Netherlands. METHODS: Persons aged ≥60 years were personally invited by mail. Those born between 01-01-1934 and 01-05-1952 (i.e., age 71.7-90.0 on 31-12-2023) received a letter with a PBA, while the others received a letter inviting them to self-schedule an appointment. National registries of sociodemographic determinants and COVID-19 vaccination were linked by a unique personal identifier. A regression discontinuity design was applied to estimate the local average treatment effect at 71.7 and 90.0 years of age among non-institutionalised adults with ≥1 prior COVID-19 vaccination. Stratified analyses were done for sociodemographic subgroups. RESULTS: The autumn 2023 vaccination coverage among non-institutionalised persons aged ≥60 years with ≥1 prior registered COVID-19 vaccination (N = 4.0 million) was 55.0%. PBA resulted in a 3.3 (95% CI 2.6-4.1) and 4.7 (95% CI 3.7-5.7) percentage point higher uptake at 71.7 and 90.0 years, respectively. Subgroup analyses showed predominantly positive results. However, statistically significant interactions between several determinants of vaccination and the PBA effect indicate that the effect size differed between subgroups. DISCUSSION: This nationwide quasi-experimental study shows that PBA is effective in increasing uptake. However, differences of the PBA effect between subgroups should be taken into account to increase equity of the vaccination programme.