Adding nudge-based reminders to financial incentives for promoting antibody testing and vaccination to prevent the spread of rubella

We study the effects of combining financial incentives with nudges to promote antibody testing and vaccination to prevent the spread of rubella. In 2019, the Japanese government began providing vouchers for free antibody testing and vaccination to men aged 40–57 years. Vouchers were automatically mailed to 40–46-year-old men in 2019. Those aged 47–57 would receive vouchers after April 2020, while they could obtain vouchers for undertaking antibody testing and being vaccinated in 2019 by applying. Focusing on this policy distinction, we conducted an online field experiment with Japanese 40–57-year-old men in February and March 2020. We randomly provided six nudge-based reminder messages recommending antibody testing and vaccination and tracked self-reported behavior until March of 2020. One nudge-based reminder with an altruistic message on fetal harm through infection from men to pregnant women significantly promoted antibody testing among the 40–46-year-old men who had already received vouchers as a financial incentive. This message could also encourage their vaccinations. In contrast, any nudge-based reminder had no promoting effect for the 47–57-year-old men who must apply for vouchers.