The authors had previously conducted a trial (termed, NUDGE-FLU) during the 2022–2023 influenza season in Denmark, where the government maintains Digital Post (an online mailbox for most citizens aged 15 years or older). As part of the NUDGE-FLU trial, the authors sent messages through Digital Post to adults aged 65 years and older and concluded that these electronic reminders could improve influenza vaccine uptake. In their Nature Medicine study, the authors were interested in whether the benefits of sending these electronic reminders were consistent across consecutive influenza seasons. The authors relied on a cohort of 881,373 older adults, who represented 70.4% of the total eligible study population in Denmark. Participants were randomly assigned into seven different groups, which influenced either the number of messages they received through Digital Post or the content of the message they received about influenza vaccinations. For instance, participants in one group were sent a standard notification about the upcoming influenza season, which included a reminder that they were eligible to receive a free vaccine. In other groups, this standard message was supplemented with text that notified participants about the benefits of influenza vaccination in limiting cardiovascular disease risk, respiratory complications or the spread of the infection to friends and family. Alternatively, participants may have received the standard message twice in the span of about two weeks or a single message that contained a link to directly book a vaccination appointment. Finally, as a control comparison, a subset of older adults did not receive any nudges or reminders about the influenza vaccine through Digital Post.
After pooling all participants who had received any kind of digital nudge, the authors observed a 0.31% increase in vaccinations by the end of the year, compared to participants who did not receive an electronic reminder. There were no significant differences in vaccination rates when considering participant age, sex, geographical location in Denmark or disease status, or whether individuals had taken part in the original NUDGE-FLU trial. Participants who received electronic reminders were also more likely to get vaccinated earlier in the year, although the authors were unable to resolve whether any single kind of reminder or letter offered a significant benefit in improving vaccination rates.
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