This paper studies non-adherence in the Danish Childhood Vaccination Program using a nationwide introduction of a vaccination reminder letter policy and administrative data from 2011–2017. First, I provide causal estimates of how the reminder letter policy affects vaccination adherence using a Regression Discontinuity Design (RDD). Second, I link parental responses to the reminder letter to parents’ causes for being non-adherent. I find that the reminder letter policy positively affects adherence. However, 72% of non-adherent parents are non-responsive to the reminder letter indicating that reluctance and not inattention is the leading cause for non-adherence. Thus, other policies beyond reminder letters – such as mandatory vaccination laws – are necessary to substantially increase vaccination coverage.

本文使用 2011 年至 2017 年在全国范围内引入的疫苗接种提醒信政策和行政数据来研究丹麦儿童疫苗接种计划的不遵守情况。首先，我使用回归不连续性设计 (RDD) 提供了关于提醒信政策如何影响疫苗接种依从性的因果估计。其次，我将家长对提醒信的反应与家长不依从的原因联系起来。我发现提醒信政策对遵守情况有积极影响。然而，72% 的不依从的父母对提醒信没有反应，这表明不情愿而不是注意力不集中是不依从的主要原因。因此，除了提醒函之外的其他政策——例如强制性疫苗接种法——对于大幅提高疫苗接种覆盖率是必要的。