This study will reveal how sending nudge-based messages to correct the false belief “I have antibodies for rubella” affects the uptake of rubella antibody testing and vaccination.
In Japan, herd immunity to rubella can be obtained by achieving a 90% antibody prevalence rate for rubella in all generations. While the rate has reached over 90% among most generations, the rate for males born between 1962 and 1978 is approximately 80%, because they were previously excluded from the routine vaccinations and have had few natural infections. Therefore, the Ministry of Health, Labor, and Welfare (MHLW) has set a policy goal of increasing the antibody prevalence rate of this generation of males from 80% to 90% to obtain herd immunity against rubella.
To achieve this goal, free coupons for rubella antibody testing and vaccination have been mailed to males of the target generation from FY2019 to FY2021 by local governments. The MHLW expected that the policy goal described above could have been achieved if approximately 1.9 million had used these coupons and received the rubella vaccination. However, as of October 2021, the number of people vaccinated remained low at about 740,000 (about 39% of the target number). Therefore, the MHLW decides to re-distribute free coupons starting also in FY2022. The coupons will be mailed to males born between 1962 and 1978 who have not received an antibody testing during FY2019 to FY2021, or who have not been vaccinated even though they are eligible for the vaccination.
Taking the results of our preliminary survey into account, we find that the subjects could form false beliefs, such as “I received the rubella vaccine when I was a child" (even though there were no routine rubella vaccinations for their generations) or “I was infected with rubella in the past" (even though they were actually infected with chickenpox or measles, not rubella). We focus on the possibility that these misperceptions may be a bottleneck of preventing them from getting tested and vaccinated. In this study, we will develop a nudge-based message to correct this belief and conduct a field experiment in cooperation with a local government in Ibaraki, Japan, to evaluate the effect of the message.
The subjects of our field experiment are males born between 1962 and 1978 who reside in that local government’s area and who have not yet been tested for rubella antibodies during FY2019 to FY2021 (N = 5,568). We employ cluster randomization at the regional level for the allocation of four experimental arms. The control group will receive coupons and a leaflet developed by the local government, while the three treatment groups will additionally receive nudge-based messages developed by us in three different ways.
We will receive anonymized administrative data from the local government on the date of the antibody test, the result of the antibody test, and the date of vaccination. Our primary outcomes are “antibody testing behavior” and “vaccination behavior”. Using these binary variables, we estimate the average effect of nudge-based interventions on vaccination, e.g., through linear probability models. Our secondary outcomes are “date of antibody test” and “vaccination date,” in addition to “whether the antibody test result was negative.” Using these date variables, we estimate the effect of the interventions on the vaccination date using, for example, a survival analysis.