Nudging COVID-19 Vaccine Uptake by Changing the Default: A Randomized Controlled Trial

Background: Although vaccination against SARS-CoV-2 is considered the central strategy against the pandemic, uptake lags behind target rates. Method: To explore whether this rate could be enhanced by a nudging strategy that exploits the status quo bias, we conducted a randomized controlled trial in northern Italy comparing vaccination acceptance among 2000 adults, ages 50 to 59 years, who were either invited to set an appointment (opt-in group) or assigned an individual appointment (opt-out group). Results: Results indicate a difference of 3.2 percentage points, which represents a 32% relative increase in the vaccination rate for the opt-out group compared with the opt-in group. Conclusions: A significant portion of those who remain unvaccinated may not hold strong beliefs against vaccination but rather tend to inaction and may therefore be nudged toward vaccination with a reduction of action required. Reluctant adults (50-59 years), who had not yet received vaccines against COVID-19, were sent letters announcing appointment availability In an RCT, the status quo option in the notices influenced the rate of vaccine acceptance Nudging via pre-scheduled appointments encouraged vaccine uptake more than invitations to schedule did Switching the default option yielded a 32% relative increase (13.1% vs. 9.9%) in vaccination.