Maintaining COVID-19 vaccine demand was key to ending the global health emergency. To help do this, many governments used chatbots that provided personalized information guiding people on where, when and how to get vaccinated. We designed and tested a WhatsApp chatbot to understand whether two-way interactive messaging incorporating behaviourally informed functionalities could perform better than one-way message reminders. We ran a large-scale preregistered randomized controlled trial with 249,705 participants in Argentina, measuring vaccinations using Ministry of Health records. The behaviourally informed chatbot more than tripled COVID-19 vaccine uptake compared with the control group (a 1.6 percentage point increase (95% confidence interval, (1.36 pp, 1.77 pp)) and nearly doubled uptake compared with the one-way message reminder (a 1 percentage point increase (95% confidence interval, (0.83 pp, 1.17 pp)). Communications tools designed with behaviourally informed functionalities that simplify the vaccine user journey can increase vaccination more than traditional message reminders and may have applications to other health behaviours.

维持 COVID-19 疫苗需求是结束全球卫生紧急状态的关键。为了帮助做到这一点，许多政府使用聊天机器人提供个性化信息，指导人们在何处、何时以及如何接种疫苗。我们设计并测试了一个 WhatsApp 聊天机器人，以了解包含行为知情功能的双向交互式消息传递是否比单向消息提醒表现更好。我们在阿根廷进行了一项大规模的预注册随机对照试验，有 249,705 名参与者参与，使用卫生部的记录测量疫苗接种情况。与对照组相比，行为知情聊天机器人的 COVID-19 疫苗接种率增加了两倍多（增加了 1.6 个百分点（95% 置信区间，（1.36 pp，1.77 pp）），与单向消息提醒相比，接种率几乎翻了一番（增加 1 个百分点（95% 置信区间，（0.83 pp，1.17 pp））。与传统的消息提醒相比，设计具有行为知情功能、简化疫苗用户旅程的通信工具可以更能提高疫苗接种率，并可能适用于其他健康行为。