Default change nudges Covid-19 vaccine uptake: 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 aged 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.