The impact of mandatory COVID-19 certificates on vaccine uptake: Synthetic Control Modelling of Six Countries
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Abstract
Background
COVID certification has been introduced, yet there are no empirical evaluations of its impact on vaccine uptake.
Methods
Mirroring an RCT, we designed a synthetic control model comparing six countries (Denmark, Israel, Italy, France, Germany, Switzerland) that introduced certification (May-August 2021), with 20 control countries. Our estimates provide a counterfactual trend estimating what would have happened in virtually identical circumstances if certificates were not introduced. The primary outcome was daily COVID-19 vaccine doses, with supplementary analyses of COVID-19 infections.
Findings
COVID-19 certification led to increased vaccinations 20 days prior to implementation, with a lasting effect up to 40 days after. Countries with lower than average pre-intervention uptake had a more pronounced increase. In France, doses exceeded 25,895 vaccines per million capita (pmc) or in absolute terms, 1,749,589 doses prior to certification and 11,434 pmc after (772,563 doses). There was no effect in countries with higher uptake (Germany) or when introduced during limited supply (Denmark). There was higher uptake for <20 years and 20-29 years. Access restrictions linked to certain settings (nightclubs, events >1,000) were associated with higher uptake <20 years. When extended to broader settings, uptake remained high in the youngest group, but also observed in older age groups. The relationship of the intervention with reported infections was difficult to assess based on available data.
Interpretation
We provide the first empirical assessment of the relationship between COVID-19 certification and vaccine uptake. Interpretation should recognise additional factors, including age eligibility changes and pandemic trajectories. We provide evidence that certification could increase vaccine uptake.
Funding and Competing Interest Statement
MCM receives funding from the Leverhulme Trust (Large Centre Grant), European Research Council (835079) and participates in UK’s SAGE SPI-B (behavioural insights) committee. The funders had no role in study design, data collection, analysis, interpretation, or writing of the report.
Research in Context
Evidence before this study
The introduction of COVID-19 certification or vaccine passports has been linked to lower self-reported vaccine intentions, yet national media and health offices report increases in vaccinations. No empirical studies could be located that had examined the impact of the implementation of mandatory COVID-19 certification on vaccine uptake.
Added value of this study
To our knowledge, this is the first empirical analysis of the relationship of the introduction of COVID-19 certification on vaccine uptake.
Implications of all the available evidence
Our study provides the first evidence that mandatory COVID-19 certification restricting access to certain settings can influence vaccine uptake for those groups affected by the intervention. Given higher vaccine complacency in certain groups, such as youth who perceive lower risks of infection, this intervention could be an additional policy lever to increase vaccine uptake and population level immunity. Future studies examining more countries and variation by eligibility criteria and factors beyond age are warranted.
Article activity feed
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SciScore for 10.1101/2021.10.08.21264718: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics not detected. Sex as a biological variable not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Table 2: Resources
No key resources detected.
Results from OddPub: Thank you for sharing your code and data.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:Limitations include a lack of access to granular daily age-based uptake for all countries and ability to examine confounders such as ethnicity or socioeconomic status. Certification was introduced at different phases during the pandemic for different reasons and across regional and national-level conditions with varying levels of age eligibility, supply, …
SciScore for 10.1101/2021.10.08.21264718: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics not detected. Sex as a biological variable not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Table 2: Resources
No key resources detected.
Results from OddPub: Thank you for sharing your code and data.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:Limitations include a lack of access to granular daily age-based uptake for all countries and ability to examine confounders such as ethnicity or socioeconomic status. Certification was introduced at different phases during the pandemic for different reasons and across regional and national-level conditions with varying levels of age eligibility, supply, vaccine hesitancy, enforcement and variation in infections and mortality. France31 and Italy32 have a history of vaccine hesitancy;31 together with Israel incentivised vaccine uptake with the use of certification for desirable events or settings.33 Whereas Belgium’s aim was to avoid the reinstatement of restrictions.34 Transferability of results to other settings should account for contextual aspects listed above.
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
Results from scite Reference Check: We found no unreliable references.
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