Keep Reminding Me to Get My Flu Shot

We studied the long-term effect of a randomized informational nudge on influenza vaccination rates through a field experiment. The study was conducted in collaboration with a major health insurer in Switzerland. A letter informing consumers about the possibility of vaccination in selected pharmacies was used as the impetus. One year later, the same nudge was repeated for half of the initial recipients, while it was discontinued for the other half. We found that the nudge was effective in the short run but failed to have persistent or additive effects in the second year. Our findings highlight the importance of annual reminders to sustain and enhance the impact of informational nudges on influenza vaccination rates. Furthermore, by linking the experiment to administrative health insurance data, we observed the impact of the nudge on not only targeted behavior (i.e., pharmacy vaccinations) but also untargeted behavior (physician vaccinations). We observed some crowding out of physician-provided vaccinations among individuals in the treatment group who had been vaccinated in the previous influenza season.