For information interventions to be effective, recipients must first engage with them. We show that engagement with repeated digital information interventions is shaped by subtle and strategically controllable signals of the information’s value. In particular, recipients’ expectations are shaped by signals from the “envelope” that surrounds a message in an information intervention. The envelope conveys clues about the message but does not reveal the message itself. When people expect the message to be valuable, delivering it in a consistent and recognizable envelope over time increases engagement relative to varying the envelope. Conversely, when people expect the message to be of little value, delivering it in a consistent and recognizable envelope decreases engagement relative to varying the envelope. We show this with two field experiments involving massive open online courses and one online survey experiment (all pre-registered, N = 439,150).

Many Americans fail to get life-saving vaccines each year, and the availability of a vaccine for COVID-19 makes the challenge of encouraging vaccination more urgent than ever. We present a large field experiment (N = 47,306) testing 19 nudges delivered to patients via text message and designed to boost adoption of the influenza vaccine. Our findings suggest that text messages sent prior to a primary care visit can boost vaccination rates by an average of 5%. Overall, interventions performed better when they were 1) framed as reminders to get flu shots that were already reserved for the patient and 2) congruent with the sort of communications patients expected to receive from their healthcare provider (i.e., not surprising, casual, or interactive). The best-performing intervention in our study reminded patients twice to get their flu shot at their upcoming doctor’s appointment and indicated it was reserved for them. This successful script could be used as a template for campaigns to encourage the adoption of life-saving vaccines, including against COVID-19.