Vaccination passes: Chariot to freedom or a Trojan horse?

An interdisciplinary collaboration to provide model-based evidence to inform policy decisions on vaccination passes and on how they shape pandemic dynamics. Do they allow us to safely navigate epidemic waves? Or can they prove treacherous, compromising all sacrifices and efforts previously made?

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Δύο γὰρ, ἐπιστήμη τε καὶ δόξα, ὧν τὸ μὲν ἐπίστασθαι ποιέει, τὸ δὲ ἀγνοεῖν.

There are in fact two things, science and opinion; the former begets knowledge, the latter ignorance.

Hippocrates of Cos, Law (Νόμος) 4.8.

This blog post is a group effort, same as our paper.

T. Krueger, K. Gogolewski, M. Bodych, A Gambin, G. Giordano, S Cuschieri, T. Czypionka, M. Perc, E. Petelos, M. Rosińska & E. Szczurek

We came together as an interdisciplinary group of passionate researchers across Europe to contribute to the fight against COVID-19 by providing model-based evidence to inform policy decisions. A few months into the pandemic, tools that operationalised status on the basis of vaccination and recovery emerged, namely, vaccination passes. Critical questions arose in terms of how they would shape pandemic dynamics. Could vaccination passes allow us to safely navigate epidemic waves whilst restoring our freedom? Or would they prove treacherous, compromising all the sacrifices and efforts made in the previous months? 

By November 2020, we had started to systematically discuss the need to examine how the implementation of this new technology and policy tool would unfold.  The vaccination programmes had by then a much clearer implementation horizon and we wanted to support the effort of informing the implementation and evidence-informed policymaking. We also hoped to be careful and diligent enough to develop a model that could withstand the emergence of new variants. Key ethical, legal, technical and scientific challenges had been identified early on,1,2 yet in the hope to regain freedom and move towards normalcy, the European Commission moved forward with the proposal for the Digital COVID Certificate to be implemented across the European Union (EU) to facilitate free movement.

The EU Digital COVID Certificate Regulation entered into application on 1 July 2021.3 EU citizens and residents were to be able to utilise their Digital COVID Certificates issued and verified across the EU, and persons who had a valid EU Digital COVID Certificate were not to be subjected to additional restrictions, such as tests or quarantine, regardless of their place of departure in the EU. Although the certificate was not developed to motivate people to vaccinate, and this was made explicitly clear in the legislation, most EU Member States did consider this practical aspect viewing it as potentially useful to increase vaccination rates. With vaccination passes very much a reality, the emergence of variants with the potential to evade immunity elicited by either natural infection or by vaccination became crucial concern. We, therefore, focused our study to examine possible consequences of the introduction of vaccination passes, taking into account waning immunity and possible resurgence due to the emergence of  variants of concern.

Assessing the impact of interventions - such as vaccines, as well as non-pharmaceutical interventions - on SARS-CoV-2 control, with due consideration to declining immunity, is particularly challenging. Our research questions were: are vaccination passes a safe and effective tool? What evidence is needed to inform their implementation? To generate potential scenarios, so as to look into the future, we had to establish parameters from the literature, on the basis of emerging evidence on vaccine effectiveness, vaccination coverage, incidence, and hospital stays. We also had to decide on reasonable assumptions and methodically establish the population groups to associate with the model compartments, i.e., vaccinated, unvaccinated, infected, recovered.

Our results demonstrate that both the Alpha and Delta SARS-CoV-2 variants inevitably lead to recurring outbreaks when measures are lifted for vaccination pass holders without precautions and re-vaccination. Our model structure is valid regardless of the considered pathogen and the core parameters can easily be adapted to different SARS-CoV-2 variants. After adapting our parameters when Delta emerged, we saw the same as before for Alpha: the benefit of vaccination passes necessitated a high (re-)vaccination and lowered fraction of the unvaccinated population. Continued vigilance and combined public health measures remained critical to manage the epidemic. Is this still the case with Omicron? The advent of Omicron clearly illustrates the potential of SARS-CoV-2 to evade immunity against prior variants.  We have, indeed, seen a lower hospitalisation and ICU rates than with Delta, but both are still out there; Delta may well re-emerge strongly in the summer and Omicron in the following autumn-winter season. Given the role cellular immunity plays, and the fact it is not as easily evaded as humoral, it is critical to comprehend that vaccination coverage is what will ultimately have the greatest impact on the evolution of further waves. Vigilance and increased preparedness, and all that this implies in terms of surveillance and access to vaccines, are fundamental.

We often had to clarify points to each other, held different views on what is possible, feasible and, even, desirable. We all, however, comprehended the difference between opinions and evidence, and considered science was the only safe compass.

We all come from different disciplines, and are of different cultures and countries across Europe. Most of us have never or rarely met in person. Yet we found that science gave us a common language and we were equally eager to test our own assumptions and perceptions on what the advent of the vaccination passes signified for how the pandemic was managed and how it would evolve. We often had to clarify points to each other, held different views on what is possible, feasible and, even, desirable. We all, however, comprehended the difference between opinions and evidence, and considered science was the only safe compass. We managed to agree on what to prioritise in our model, on what parameters to examine and on the assumptions to be made. In the end, not only we all gained knowledge from our model regarding the implications of different policies related to vaccination passes, but also learned a lot from one another and discovered the strength of complementary and synergistic approaches to a research endeavour. Furthermore, there was reward for the effort and confidence in our work; the predictive value of the model was high in the context of the tides of Delta and Omicron, when boosters have ensured that people and systems across Europe, and in many countries across the globe, have remained well protected against severe disease.

We have been fortunate to benefit from rapidly developed effective vaccines. An unprecedented feat, which would have been considered impossible a few years before. Lately, we have been seeing a widespread misconception propagated with certainty, and against clear messaging from the World Health Organization and warnings from scientists across disciplines;4 namely, that the virus has been rapidly evolving to a more benign form. Lessons from the past, the emergence of strains with the current transmissibility and vaccine breakthrough infections clearly demonstrate the need to remain vigilant. To effectively address the threat posed by an evolving virus to our health systems and our global village, we need to learn and improve our collective response in an equitable manner. This can only be achieved by working together to meet the global needs for vaccine development and production, to enhance mechanisms available to monitor new variant emergence and vaccine effectiveness and safety, and to ensure concerted action to combat both epidemics and infodemics.5  We remain optimistic on what can be achieved, perhaps, because of the experience gained in our diverse team. We firmly believe interdisciplinary cross-border collaboration is the way forward; from small groups like ours to multi-stakeholder partnerships, addressing key questions one by one and improving  resilience and preparedness.


1. Kofler N, Baylis F. Ten reasons why immunity passports are a bad idea. Nature. 2020 May;581(7809):379-381. doi: 10.1038/d41586-020-01451-0. PMID: 32439992.

2. Voo TC, Reis AA, Thomé B, Ho CW, Tam CC, Kelly-Cirino C, Emanuel E, Beca JP, Littler K, Smith MJ, Parker M, Kass N, Gobat N, Lei R, Upshur R, Hurst S, Munsaka S. Immunity certification for COVID-19: ethical considerations. Bull World Health Organ. 2021 Feb 1;99(2):155-161. doi: 10.2471/BLT.20.280701. Epub 2020 Dec 1. PMID: 33551509; PMCID: PMC7856365.

3. European Commission. EU Digital COVID Certificate. [Last accessed: March 02, 2022].

4. World Health Organization. Enhancing response to Omicron SARS-CoV-2 variant: Technical document. January 21, 2022. [Last accessed: March 2, 2022].

5. World Health Organization. Infodemiology: Progressing on the public health research agenda for managing infodemics in COVID-19 Research and Innovation - Powering the world’s pandemic response – now and in the future. February 2022. [Last accessed: March 2, 2022].

Elena Petelos

Lecturer in EBM – Senior Research Fellow in Public Health, University of Crete and Maastricht University