The COVID-19 pandemic prompted governments to implement unprecedented policies, ranging from elimination strategies to mitigation efforts focused on protecting health systems and buying time until vaccines or treatments became available. Public health measures included venue closures, social contact limitations, and travel restrictions. COVID certificates—verifying vaccination, recovery, or negative tests—allowed for targeted interventions based on individual transmission risk. While ethically and politically contentious, proponents highlight their potential to facilitate social interactions and, increasingly recognized, boost vaccine uptake. Vaccine hesitancy and refusal posed significant challenges to achieving high vaccination coverage. Policymakers have historically used various methods to improve uptake, from communication strategies to financial incentives and mandates. COVID certificates emerged as a novel tool during the pandemic, necessitating further research. This study examines the impact of COVID certificates on vaccination, health, and the economy in France, Germany, and Italy. These countries introduced these certificates around the same time to regulate domestic access to public venues. They also shared comparable vaccine supply, demographics, health infrastructure, and economic profiles. The aim is to quantify the incentive effect of COVID certificates on vaccination and determine their contribution to averting adverse health and economic consequences. The results can inform future decision-making on the use of COVID certificates.

The study draws upon existing literature on innovation diffusion theory, which models how new ideas and technologies spread within a population. This theory has been applied to the uptake of medical innovations, including vaccines. The study references prior research on the effects of COVID-19 certificates on vaccine uptake, noting that their results are consistent with, but generally more substantial than, those from survey-based estimates and other studies using cross-country or state comparisons with different methodologies. The authors highlight the lack of studies analyzing the long-term effects of COVID certificates and the need for further investigation into their broader effects on epidemic development and long-term social and economic costs and benefits.

The study uses a counterfactual approach, employing innovation diffusion theory to model vaccine uptake without COVID certificates. This method, frequently used to study the uptake of medical innovations, incorporates a 'coefficient of innovation' (rate of vaccination independent of others) and a 'coefficient of imitation' (rate influenced by the share of vaccinated individuals). The model, widely used for its tractability and interpretability, is applied to data from France, Germany, and Italy, estimating the parameters through least-squares fitting over periods before the announcement of COVID certificates and then extending them to the end of 2021. To assess robustness, the study incorporates synthetic control, creating counterfactuals based on a weighted average of countries that didn't implement COVID certificates. This method, while providing a valuable check, faces limitations due to the increasing adoption of COVID certificates across countries, diminishing the size of the control group and raising questions about the independence of control countries' policies. The impact on health outcomes is estimated by calculating the number of averted hospital admissions and deaths using vaccine effectiveness estimates from the literature, accounting for various vaccines, waning immunity, and age-specific data. The economic impact is analyzed using the OECD Weekly Tracker, a high-frequency GDP proxy, to capture the effects of varying vaccination rates on weekly GDP. The relationship between vaccination and GDP is estimated using a closed-form model, controlling for health outcomes, trade partner effects, and temperature.

The introduction of COVID certificates was associated with significant increases in vaccine uptake. In France, the increase is estimated at 13.0 percentage points (95% CI 9.7–14.9), 6.2 (2.6–6.9) p.p. in Germany, and 9.7 (5.4–12.3) p.p. in Italy. These increases translated to averted deaths: 3979 (3453–4298) in France, 1133 (–312–1358) in Germany, and 1331 (502–1794) in Italy. GDP losses were also prevented: €6.0 (5.9–6.1) billion in France, €1.4 (1.3–1.5) billion in Germany, and €2.1 (2.0–2.2) billion in Italy. The impact of COVID certificates on vaccine uptake was larger among younger populations in France and Italy. The effect was significant in France and Italy throughout the study period, but only significant in Germany from late November 2021 when the use of certificates extended to workplaces. The study found no significant spillover effects between countries. Regarding health outcomes, substantial numbers of hospital admissions were also prevented, with the largest impact observed in France (32,065 additional admissions estimated in the counterfactual scenario). The effect on ICU admissions is notable in France, potentially averting lockdown conditions. The economic analysis indicates a positive relationship between vaccination rates and GDP. A 1 percentage point increase in vaccination rates was associated with a 0.052 percentage point increase in weekly GDP (0.033–0.070). This signifies that without the COVID certificates, weekly GDP would have been lower in all three countries, highlighting the economic benefits of the policy.

The findings suggest a robust positive association between the introduction of COVID certificates and increased vaccination rates, leading to significant improvements in health and economic outcomes in France, Germany, and Italy. Although this study demonstrates a strong association, it cannot directly infer causality. The analysis relies on estimated increases in vaccine uptake and does not account for potential alterations in epidemic dynamics or influences on other policy choices. Further research is needed to fully understand the causal mechanisms and the long-term effects. Despite similar contexts (large EU countries, slowing vaccination campaigns, rising infections), the magnitude of the impact varied across countries. This variation may be attributable to differences in the way certificates were introduced, their enforcement, and the timing of announcements. Future studies should examine these factors and explore the broader effects of COVID certificates on the epidemic's trajectory. COVID certificates offer an attractive alternative to vaccine mandates, incentivizing vaccination or testing rather than imposing penalties. However, government policy decisions should also consider vaccine and test supply, political trust, accessibility for marginalized groups, and international coordination to prevent regional disparities.

This study demonstrates a strong association between the implementation of COVID certificates and increased vaccination rates, reduced health consequences, and improved economic outcomes in France, Germany, and Italy. While not establishing direct causality, the findings highlight the potential benefits of this policy instrument. Future research should focus on clarifying the causal mechanisms, exploring long-term impacts, and examining the interplay between policy design, implementation, and effectiveness. Further research should also focus on exploring the long-term consequences and the role of various contextual factors to refine our understanding of this policy's overall impact.

The study's reliance on counterfactual methods prevents a direct causal inference. The innovation diffusion model, while widely used, assumes constant parameters and no major exogenous shocks, which might be violated in the context of evolving viral variants and changing public health policies. The synthetic control method also faces limitations regarding the size of the control group and potential interdependencies between countries' policies. The study also does not consider long-term effects or the potential for unintended consequences, highlighting the need for further research exploring these areas.