Nudging COVID-19 Vaccination of Young Adults in Japan: A Field Experiment

Last registered on September 08, 2022

Pre-Trial

Trial Information

General Information

Title
Nudging COVID-19 Vaccination of Young Adults in Japan: A Field Experiment
RCT ID
AEARCTR-0007930
Initial registration date
July 07, 2021

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
July 07, 2021, 11:02 AM EDT

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Last updated
September 08, 2022, 1:44 AM EDT

Last updated is the most recent time when changes to the trial's registration were published.

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Primary Investigator

Affiliation
Tohoku Gakuin University

Other Primary Investigator(s)

PI Affiliation
National Institute of Infectious Diseases
PI Affiliation
City of Tsukuba
PI Affiliation
Osaka University

Additional Trial Information

Status
On going
Start date
2021-07-08
End date
2025-03-31
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Abstract
Some studies showed that young adults have lower intentions of COVID-19 vaccination than older people. Our previous study found that nudge-based messages providing information on others’ decisions and behaviors could strengthen the vaccination intentions of the older people, but do not have the same effects for the young adults (Sasaki, Saito, & Ohtake, 2021). In other words, we have not yet found an effective message to encourage the vaccination of the young adults.

This study again explores nudge-based messages that can encourage COVID-19 vaccination of young adults with low vaccination intentions at baseline. Our preliminary analysis indicates the possibility that the high need for going out and a rise in altruism among younger people may close the gap in vaccination intentions between older and younger people. One foreign study reported that the message, “Full shot reserved for you,” has a large effect in promoting people to receive the seasonal flu vaccine (Milkman et al., 2021). The similar message may be effective for promoting COVID-19 vaccination of people in Japan. Taking the pre-analysis and the foreign study into account, we will develop nudge-based messages for the vaccination of young adults in Japan.

Collaborating with a local government in Japan, we conduct a field experiment toward 4,000 young adults (30-39 years old) residing in that area. In the experiment, we randomly divide the subjects into either of one control group or three treatment groups. The local government mails coupons, which are required for COVID-19 vaccination bookings and post-vaccination records, to their residents. In the treatment groups, we respectively put a sticker with a nudge-based message on the envelope to mail the coupons.

The local government merge information on which group they belong to, whether they receive the COVID-19 vaccine, and when they receive it, and share the list with us, the research team, after it has been completely anonymized.

Our first analysis evaluates the impacts of three nudge-based messages on the likelihood that the subjects receive the COVID-19 vaccine, by using the linear probability model, etc. Our second analysis evaluates the messages’ impacts on the timing of when they receive it, by using the Cox's proportional hazards model, etc.

References:
- Sasaki, S., Saito, T., and Ohtake, F. 2021. Nudges for COVID-19 voluntary vaccination: How to explain peer information? Osaka University Discussion Papers In Economics And Business, No.2107.
- Milkman, K.L. et al. 2021. A Mega-Study of Text-Based Nudges Encouraging Patients to Get Vaccinated at an Upcoming Doctor’s Appointment. Proceedings of the National Academy of Sciences, 118(20), e2101165118.
External Link(s)

Registration Citation

Citation
Sasaki, Shusaku et al. 2022. "Nudging COVID-19 Vaccination of Young Adults in Japan: A Field Experiment." AEA RCT Registry. September 08. https://doi.org/10.1257/rct.7930
Experimental Details

Interventions

Intervention(s)
We randomly assign experimental subjects to either of one control group or three treatment groups. The local government mails coupons, which are required for COVID-19 vaccination bookings and post-vaccination records, to their residents. In the treatment groups, we respectively put a sticker with a nudge-based message on the envelope to mail the coupons.
Intervention Start Date
2021-07-08
Intervention End Date
2022-03-31

Primary Outcomes

Primary Outcomes (end points)
Whether you received the COVID-19 vaccine or not (binary).
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
When you received the COVID-19 vaccine (date information).
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
We randomly assign experimental subjects to either of one control group or three treatment groups. The local government mails coupons, which are required for COVID-19 vaccination bookings and post-vaccination records, to their residents. In the treatment groups, we respectively put a sticker with a nudge-based message on the envelope to mail the coupons.
Experimental Design Details
Not available
Randomization Method
Cluster randomization by the local government. We explained the randomization procedure in Experimental Design Details.
Randomization Unit
Clusters (Bundles, which include 25 envelopes respectively).
Was the treatment clustered?
Yes

Experiment Characteristics

Sample size: planned number of clusters
160 clusters
Sample size: planned number of observations
4,000 individuals
Sample size (or number of clusters) by treatment arms
1,000 individuals (40 clusters) in the control group, 1,000 individuals (40 clusters) in the treatment group A, 1,000 individuals (40 clusters) in the treatment group B, 1,000 individuals (40 clusters) in the treatment group C.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
IRB

Institutional Review Boards (IRBs)

IRB Name
Graduate School of Economics, Osaka University IRB
IRB Approval Date
2021-06-21
IRB Approval Number
N/A