The effects of monetary incentives on COVID-19 vaccination uptake
| ISRCTN | ISRCTN59503725 |
|---|---|
| DOI | https://doi.org/10.1186/ISRCTN59503725 |
| Secondary identifying numbers | MoInVax-RV-2021 |
- Submission date
- 26/10/2021
- Registration date
- 28/10/2021
- Last edited
- 10/02/2025
- Recruitment status
- No longer recruiting
- Overall study status
- Completed
- Condition category
- Infections and Infestations
Plain English Summary
Background and study aims
Vaccination is one of the most effective ways to control the spread of COVID-19. However, many high-income countries struggle to reach levels of vaccination that approach herd immunity. According to the European Centre for Disease Control and Prevention, only about 64% of the European population is fully vaccinated. To increase vaccination rates, it is critically important to encourage those who remain hesitant and mobilize those who are willing to get vaccinated but haven't followed through. To do so, numerous local and state governments have started experimenting with various forms of monetary incentives, ranging from small financial payouts to large-sum lotteries. The effectiveness of these initiatives is not yet clear. The aim of this study is therefore to test if a monetary incentive motivates unvaccinated people to get a COVID-19 vaccination. The researchers also want to know if a monetary incentive motivates people to convince other people to get vaccinated.
Who can participate?
The study will take place in the city of Ravensburg, Germany. All residents of the city aged 18 years or older will receive a letter from the city's mayor inviting them to get vaccinated at one of seven public vaccination clinic events.
What does the study involve?
All addresses within the city will be randomly divided into two groups (Group A and B). In Group A, one resident per address will be randomly selected. These people form the treatment group. All other residents (the remaining residents in Group A and all residents in Group B) will form the control group. Members of the treatment group will receive a letter from the city's mayor inviting them to get vaccinated at one of seven public vaccination clinic events. The letter offers a voucher of 20 Euros if the recipient gets vaccinated and another 20 Euros voucher if more than 900 people get vaccinated. The second voucher can also be redeemed by recipients who already have been vaccinated. They need to convince somebody else to get vaccinated (as verified by any other resident handing in the treatment recipient's letter during vaccination). The residents in the control group will receive the same letter but without any monetary incentives. At the end of the study, the researchers will compare the share of people who got vaccinated in the treatment group with those in the control group. They will also compare the share of people in Group A who did not receive a monetary incentive and got vaccinated with the share of people in Group B who got vaccinated. Additionally, the researchers will compare the share of people in the treatment and control group who visited the website mentioned in the letter.
What are the possible benefits and risks of participating?
If residents decide to get vaccinated against COVID-19, they benefit from the extensive protection offered against the dangers of a COVID-19 infection (especially, reducing the risk of hospitalization and death). Residents in the treatment group additionally benefit from the monetary incentive. The risks are the limited risks associated with the COVID-19 vaccination.
Where is the study run from?
Zeppelin University (Germany)
When is the study starting and how long is it expected to run for?
October 2021 to December 2021
Who is funding the study?
The involved researchers are paid by their universities (Zeppelin University (Germany), Georgetown University (USA), and University of Hamburg (Germany). The monetary incentives are financed by the city of Ravensburg (Germany).
Who is the main contact?
Dr Florian Keppeler
florian@ps.au.dk
Contact information
Scientific
Aarhus University
Department of Political Science
Bartholins Allé 7
Building 1340, 352
Aarhus C
8000
Denmark
 ORCID ID |
0000-0002-5984-0114 |
|---|---|
| florian@ps.au.dk |
Study information
| Study design | Single-center interventional two-stage (individual-and-cluster level) randomized trial |
|---|---|
| Primary study design | Interventional |
| Secondary study design | Two-stage (individual-and-cluster) randomized controlled trial |
| Study setting(s) | Community |
| Study type | Prevention |
| Participant information sheet | No participant information sheet available |
| Scientific title | Cluster-level spillover randomized controlled trial to assess the impact of monetary incentives on COVID-19 vaccination uptake among German adults |
| Study acronym | MoInVax |
| Study hypothesis | H1-1 (direct or "total" effect #1): Offering a set of monetary incentives increases the number of unique website visits (on a municipal webpage with information on COVID-19 vaccination) among treated subjects in treatment clusters compared to equivalent subjects in control clusters (i.e., in each control cluster, the person who would have received the treatment letter had they been assigned to a treatment cluster). H1-2 (direct or "total" effect #2): Offering a set of monetary incentives increases COVID-19 vaccinations (tracked at seven city vaccinations events) among treated subjects in treatment clusters compared to equivalent subjects in control clusters (i.e., in each control cluster, the person who would have received the treatment letter had they been assigned to a treatment cluster). H2 (spillover effect): Offering a set of monetary incentives increases COVID-19 vaccinations among untreated individuals in treatment clusters compared to untreated subjects in control clusters (minus the individual who would have received a treatment letter in the control cluster if they were assigned to a treatment cluster). H3-1 (overall effect #1): Offering a set of monetary incentives increases unique website visits among treated and untreated individuals in treatment clusters compared to untreated subjects in control clusters. H3-2 (overall effect #2): Offering a set of monetary incentives increases COVID-19 vaccinations among treated and untreated individuals in treatment clusters compared to untreated subjects in control clusters. |
| Ethics approval(s) | Approved 29/10/2021, Ethics Commission of the Zeppelin University (Dr. Ute Lucarelli, Zeppelin University, Am Seemooser Horn 20, 88045 Friedrichshafen, Germany; +49 (0)7541 6009 1114; ethikkommission@zu.de) |
| Condition | COVID-19 (SARS-CoV-2 infection) |
| Intervention | Current intervention as of 04/11/2021: The study will be conducted in the city of Ravensburg, Germany. All residents of the city (age 18 years and older) will be subject to the trial. Treatment assignment follows a two-stage randomization process. In the first stage, all housing addresses within the city will be randomized into two groups (i.e., intervention group and control group). In the second stage, one resident of each address in both groups will be randomly selected (a "cluster representative"). The cluster representatives in the intervention group only will be sent the intervention letter. All remaining residents will be sent the control letter. The treatment group will receive a letter from the mayor of the city inviting them to get a COVID-19 vaccination at one of seven public vaccination events. The letter offers two financial incentives. If the recipient is not already vaccinated and gets vaccinated at the vaccination events, they will receive 20 Euros (in the form of a shopping voucher). Additionally, another 20 Euro incentive is offered if more than 900 city residents get vaccinated at one of the seven vaccination events. If the recipient is already vaccinated, they can still get the second incentive if they give the treatment letter to someone else and that individual brings it to one of the seven vaccination events, gets vaccinated, and more than 900 city residents get vaccinated during the one of the seven vaccination events. The control group will get the same letter as the treatment group but without the offer of monetary incentives. For the analysis, all residents living at the same address will be treated as members of the same social network. The researchers will test an alternative operationalization of a social network by considering all residents with the same last name who reside are part of the same address cluster as members of the same social network. The entire known population of the city (based on the official registry of residents) will be randomized. The randomization will be conducted in R (version 4.1.1) using the function "sample" with the seed set to 2021. The cluster-level randomization will be blocked by cluster size. Previous intervention: The study will be conducted in the city of Ravensburg, Germany. All residents of the city (age 18 years and older) will be subject to the trial. Treatment assignment follows a two-stage randomization process. In the first stage, all housing addresses within the city will be randomized into two groups (i.e., intervention group and control group). In the second stage, one resident of each address in both groups will be randomly selected (a "cluster representative"). The cluster representatives in the intervention group only will be sent the intervention letter. All remaining residents will be sent the control letter. The treatment group will receive a letter from the mayor of the city inviting them to get a COVID-19 vaccination at one of seven public vaccination events. The letter offers two financial incentives. If the recipient is not already vaccinated and gets vaccinated at the vaccination events, they will receive 20 Euros (in the form of a shopping voucher). Additionally, another 20 Euro incentive is offered if more than 750 city residents get vaccinated at one of the seven vaccination events. If the recipient is already vaccinated, they can still get the second incentive if they give the treatment letter to someone else and that individual brings it to one of the seven vaccination events, gets vaccinated, and more than 750 city residents get vaccinated during the one of the seven vaccination events. The control group will get the same letter as the treatment group but without the offer of monetary incentives. For the analysis, all residents living at the same address will be treated as members of the same social network. The researchers will test an alternative operationalization of a social network by considering all residents with the same last name who reside are part of the same address cluster as members of the same social network. The entire known population of the city (based on the official registry of residents) will be randomized. The randomization will be conducted in R (version 4.1.1) using the function "sample" with the seed set to 2021. The cluster-level randomization will be blocked by cluster size. |
| Intervention type | Behavioural |
| Primary outcome measure | 1. Information uptake measured by whether a participant visits the informational website mentioned in the letter. The website is prominently displayed in both treatment and control letters. Each URL is unique to the individual recipient. Measured using server logs for the provided unique links from 05/11/2021 to 13/12/2021. 2. Vaccination uptake measured via an on-site record of administered vaccinations during the seven public vaccination events at 13/11/2021, 19/11/2021, 20/11/2021, 26/11/2021, 27/11/2021, 10/12/2021, and 11/12/2021 |
| Secondary outcome measures | There are no secondary outcome measures |
| Overall study start date | 01/10/2021 |
| Overall study end date | 13/12/2021 |
Eligibility
| Participant type(s) | All |
|---|---|
| Age group | Mixed |
| Lower age limit | 18 Years |
| Sex | Both |
| Target number of participants | All 10,036 address clusters of the city (a total of 41,881 residents). On average 4.17 residents per cluster will be included. |
| Total final enrolment | 796 |
| Participant inclusion criteria | 1. Residents of the city of Ravensburg 2. Aged 18 years or older |
| Participant exclusion criteria | 1. The inmates of the local prison (the city’s largest address cluster) 2. Residents of the cities’ second-largest address cluster (with 75 residents) |
| Recruitment start date | 10/11/2021 |
| Recruitment end date | 11/12/2021 |
Locations
Countries of recruitment
- Germany
Study participating centre
Ravensburg
88212
Germany
Sponsor information
University/education
Am Seemooser Horn 20
Friedrichshafen
88045
Germany
| Phone | +49 (0)7541 6009-0 |
|---|---|
| puma@zu.de | |
| Website | https://www.zeppelin-university.com/ |
"ROR" |
https://ror.org/05tbp1g38 |
Funders
Funder type
University/education
No information available
Government organisation / Local government
- Alternative name(s)
- University of Hamburg, UH
- Location
- Germany
Private sector organisation / Universities (academic only)
- Alternative name(s)
- Collegii Georgiopolitam, Georgetown College, GU
- Location
- United States of America
No information available
Results and Publications
| Intention to publish date | 31/03/2024 |
|---|---|
| Individual participant data (IPD) Intention to share | Yes |
| IPD sharing plan summary | Stored in publicly available repository |
| Publication and dissemination plan | Planned publication in a high-impact peer-reviewed journal |
| IPD sharing plan | Current IPD sharing statement: The datasets will be stored at Zenodo (https://zenodo.org/) and made available after publication of the findings in a scientific journal. There will be no restrictions for accessing the data, and it will be available as long as Zenodo provides this service. It will include anonymized raw data for all treated patients in the treatment and control arm. This includes information about the treatment arm, randomization block, address cluster, type of vaccination, vaccination event, information uptake, and demographic data as long as it cannot be used to de-anonymize participants. We will use k-anonymity to avoid de-anonymization. Anonymized data can be shared without patients' consent. _____ Previous IPD sharing statement: The data-sharing plans for the current study are unknown and will be made available at a later date |
Study outputs
| Output type | Details | Date created | Date added | Peer reviewed? | Patient-facing? |
|---|---|---|---|---|---|
| Dataset | Datasets can be downloaded from OSF | 22/12/2023 | No | No | |
| Preprint results | 16/11/2023 | 22/12/2023 | No | No | |
| Results article | 22/01/2024 | 29/01/2024 | Yes | No | |
| Results article | 03/02/2025 | 10/02/2025 | Yes | No |
Editorial Notes
10/02/2025: Publication reference added.
29/01/2024: Publication reference added.
22/12/2023: The following changes have been made:
1. Preprint reference added.
2. A data link has been added.
13/12/2023: The intention to publish date was changed from 31/12/2023 to 31/03/2024.
11/08/2023: The following changes have been made:
1. The study contacts were amended and the plain English summary was updated accordingly.
2. The intention to publish date was changed from 31/01/2023 to 31/12/2023.
30/12/2021: The final enrolment number (of clusters) has been added.
12/11/2021: The following changes have been made:
1. The recruitment start date has been changed from 05/11/2021 to 10/11/2021.
2. The IPD sharing statement has been updated and the IPD sharing summary changed accordingly.
04/11/2021: The intervention has been updated and the plain English summary has been updated to reflect this change.
01/11/2021: The ethics approval was added.
27/10/2021: Trial's existence confirmed by Stadt Ravensburg.
