Influenza vaccination rates remain suboptimal despite effectiveness in preventing influenza infection and related complications. We investigated whether behavioural nudges, delivered via a governmental electronic letter system, would increase influenza vaccination uptake among older adults in Denmark. We did a nationwide, pragmatic, registry-based, cluster-randomised implementation trial during the 2022–23 influenza season in Denmark. All Danish citizens aged 65 years or older or turning 65 years by Jan 15, 2023 were included. We excluded individuals living in nursing homes and individuals who had an exemption from the Danish mandatory governmental electronic letter system. Households were randomly assigned (9:1:1:1:1:1:1:1:1:1) to usual care or nine different electronic letters designed on the basis of different behavioural nudging concepts. Data were sourced from nationwide Danish administrative health registries. The primary endpoint was receipt of influenza vaccination on or before Jan 1, 2023. The primary analysis assessed an analytical set of one randomly selected individual per household, and a sensitivity analysis included all randomly assigned individuals and accounted for within-household correlation. The trial is registered with , . We identified 1 232 938 individuals aged 65 years or older in Denmark and excluded 56 436 (4·6%) individuals living in nursing homes and 211 632 (17·2%) with an exemption from the electronic letter system. We randomly assigned 964 870 (78·3%) participants across 691 820 households. Compared with usual care, influenza vaccination rates were higher in the group receiving an electronic letter highlighting potential cardiovascular benefits of vaccination (81·00% 80·12%; difference 0·89 percentage points [99·55% CI 0·29–1·48]; p<0·0001) and the group receiving repeated letters at randomisation and at day 14 (80·85% 80·12%; difference 0·73 percentage points [0·13–1·34]; p=0·0006). These strategies improved vaccination rates across major subgroups including those with and without established cardiovascular disease. The cardiovascular gain-framed letter was particularly effective among participants who had not been vaccinated for influenza in the previous season (=0·0002). A sensitivity analysis of all randomly assigned individuals accounting for within-household clustering yielded similar findings. Electronically delivered letters highlighting potential cardiovascular benefits of influenza vaccination or sent again as a reminder significantly increased vaccination uptake across Denmark. Although the magnitude of effectiveness was modest, the low-touch, inexpensive, and highly scalable nature of these electronic letters might be informative for future public health campaigns. Sanofi.

中文翻译：

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通过电子推动提高丹麦流感疫苗接种率：一项全国性、务实、基于登记的随机实施试验

尽管可以有效预防流感感染和相关并发症，但流感疫苗接种率仍然不理想。我们调查了通过政府电子信件系统提供的行为推动是否会增加丹麦老年人对流感疫苗的接种率。我们在 2022-23 流感季节期间在丹麦进行了一项全国性的、务实的、基于登记的、整群随机的实施试验。所有年满 65 岁或以上或到 2023 年 1 月 15 日年满 65 岁的丹麦公民均包括在内。我们排除了居住在疗养院的个人以及享有丹麦强制性政府电子信件系统豁免的个人。家庭被随机分配（9:1:1:1:1:1:1:1:1:1）接受常规护理或根据不同行为助推概念设计的九种不同的电子信件。数据来自丹麦全国行政卫生登记处。主要终点是在 2023 年 1 月 1 日或之前接种流感疫苗。主要分析评估了每个家庭随机选择一名个人的分析集，敏感性分析包括所有随机分配的个人并考虑了家庭内相关性。该试验已在 , 注册。我们确定了丹麦 1 232 938 名 65 岁或以上的人，排除了居住在疗养院的 56 436 名 (4·6%) 人和 211 632 名 (17·2%) 免于电子信件系统的人。我们随机分配了 691 820 个家庭的 964 870 名 (78·3%) 参与者。与常规护理相比，收到强调疫苗接种对心血管潜在益处的电子信件的组中，流感疫苗接种率较高（81·00% 80·12%；差异 0·89 个百分点 [99·55% CI 0·29–1] ·48]；p<0·0001) 以及在随机分组和第 14 天收到重复信件的组 (80·85% 80·12%；差异 0·73 个百分点 [0·13–1·34]；p= 0·0006）。这些策略提高了主要亚组的疫苗接种率，包括患有和未患有心血管疾病的人群。心血管增益框架信对于上一季节未接种流感疫苗的参与者特别有效（=0·0002）。对所有随机分配的个人进行家庭内聚类的敏感性分析得出了类似的结果。以电子方式发送的信件强调了流感疫苗接种对心血管的潜在益处，或再次发送作为提醒，显着提高了丹麦各地的疫苗接种率。尽管有效性不大，但这些电子信件的低接触、廉价和高度可扩展的性质可能会为未来的公共卫生运动提供信息。赛诺菲。