Authors: Miquel Oliu-Barton, associate professor at Paris-Dauphine University; Bary Pradelski, associate professor at the CNRS, associate member of the Oxford-Man Institute

With Covid-19 vaccines on the horizon, attention is now on how to distribute them once they are available. This involves two different scales. On the one hand, how should vaccine doses be distributed between zones (continents, countries, and regions [1]). On the other hand, how should the vaccine be allocated within a given zone [2]. The first question has received much attention, so we shall focus on the second one. How to roll out vaccines within a zone to minimise the number of severe cases of Covid-19?

The traffic-light system

The European Union has recently adopted the traffic light system, a common plan to manage the pandemic (Council of the European Union, 2020, 13 October). It agrees in its key aspects with the green-zoning proposal (Oliu-Barton & Pradelski, 2020a) we circulated to the European Commission in early May. It is based on four principles: (1) divide each country into smaller zones; (2) label them green, yellow or red according to common epidemiological criteria (the virus is under control in green zones); (3) progressively return to normal in green zones, but adopt more stringent measures in other ones; (4) allow travelling between green zones, but limit other travels (for example, require a negative test or a quarantine) [3].

The traffic light system is an important step to halt the spread of Covid-19 while restoring safe mobility across the continent. Harmonising the wide-spread use of a colour code at a regional – rather than national – level is important to avoid worst-in-class measures. Further, its adoption early on in the pandemic by several countries, including Spain and France, has proven that it is politically and socially acceptable. Finally, the plan sets the ground for common policies which depend on the epidemiological situation of each zone; vaccine deployment being one of the most urgent topics.

Vaccinating by zones

The dominating question is: who to vaccinate first? So far, the discussion has focused on individuals’ characteristics such as age and medical preconditions, but also considerations regarding the environment they live or work in. While the importance of these factors are not questioned, we propose a more efficient vaccination policy considering not only an individual’s characteristics but also the colour (or epidemiological status) of their zone.

We propose a more efficient vaccination policy considering not only an individual’s characteristics but also the colour of their zone

To be effective in halting the spread of the virus, the distinction between green, yellow and red zones requires not only the use of common criteria and similar public health measures dependent on the colour, but also colour-dependent mobility restrictions. The latter are needed to substantially reduce the risk of re-importation and thus a resurgence of the virus in green zones.

To illustrate the key insight of a colour-dependent vaccination policy, consider two regions with opposing epidemiological situations: a red zone with a particularly high incidence of the virus (for example, Madrid), and a green zone where the incidence is close to 0 (for example, Crete). In the former, priority should be given to people at risk in order to minimise the number of severe cases of Covid-19 in the short run. For the latter, priority should also be given to incoming or returning travellers to reduce the risk of a future re-importation. Imposing a vaccine (or a quarantine, negative tests, or a positive serology) to travellers builds a protecting ring around the green zone.

Zoning and vaccination in Spain

As mentioned earlier, Spain was among the first countries to adopt a colour-code map by the end of April. Its 59 continental provinces and islands were grouped into phases between zero and three. Phase 0 corresponded to red, phases 1 and 2 to yellow, and phase 3 to green. The plan was to determine the different phases using common, objective criteria; then a group of experts would determine the restrictions to apply to provinces dependent on the phase they were currently in.

In reality, however, neither the criteria nor the ultimate decision-makers were known, and public health measures were lifted under increasing political pressures. The ongoing discussions regarding the delimitation of zones, the criteria for the different phases and the resulting public health measures have clearly jeopardised the strategy’s effectiveness. Without the adoption of pre-defined, common and objective criteria the zoning strategy cannot be effective.

Setting up an efficient, colour-based vaccination policy can be the key to minimise the health, economic, social and political damages caused by Covid-19

Regarding vaccination, Spain expects to have around three million vaccine doses by the beginning of 2021, that is 10% of the European order – according to the Spanish Minister of Health, Salvador Illa (interview on RAC1, 16 October 2020). When asked about the vaccine distribution among regions, the Minister invoked the principles of “proportionality and equity”, but did not further specify how fairness should be defined. Further, Illa mentioned the use of technical and population-related criteria to determine the priority for a vaccine. In particular, people at risk and people who are directly in contact with them will be prioritised. Finally, the Minister declared its willingness to adopt common criteria, and thus to go back to the original plan.

Setting up an efficient, colour-based vaccination policy – based on objective epidemiological criteria – can be the key to minimise the health, economic, social and political damages caused by Covid-19. We should avoid the confusion that has reigned between the first and second waves of the pandemic.

Vaccination policy proposal

Individuals’ characteristics

The coronavirus is transmitted by physical proximity. Both the probability of transmission from one person to another and the risk of contracting a severe form of Covid-19 vary across the population. Furthermore, the physical proximity network – which is the relevant structure to study the spread of the virus – has a hierarchical structure, from households to communities, cities, countries, and even continents.

Considering these aspects, we can now discuss four categories under which an individual may belong:

Direct and indirect effects of vaccination

Our proposal considers the heterogeneity of zones next to the heterogeneity of individuals. Because of time and resource limitations, two complementary effects of vaccination should be effectively balanced: (A) protecting vaccinated individuals from infection (direct protection) and (B) inhibiting them from passing on the virus to others (indirect protection).

Remarkably, the vaccination of health workers provides both direct and indirect protection; not only are these workers highly exposed to the virus, but they are also in contact with people at risk. For this reason, regardless of the epidemiological situation of a zone, health workers and people at risk are the natural targets for direct protection, and prioritising them is the consensus among policymakers. By contrast, travellers and connectionists are particularly important for indirect protection, as their vaccination would considerably reduce the risk of re-importation.

Health workers and people at risk are the natural targets for direct protection

Integrating the distinction between (A) and (B) in a potential vaccination policy is realistic, yet differs from the usual framework. In France, for instance, while the notion of indirect protection is present in the reports from the Conseil Scientifique [4] and the Haute Autorité de Santé [5], the priority for vaccination is established taking only (A) into account. The reason for such an omission may be the absence of a clear zoning strategy. Indeed, without mobility restrictions in place, the entirety of France should be considered as one single zone — a red zone, as long as the virus actively circulates somewhere in the country. This leaves green zones at an increased risk of re-importation, which could be avoided by combining mobility restrictions and an additional focus on (B).

A vaccination policy for green zones

Our proposal consists of the following steps:

1. Identification of zones and classification of individuals.
   • Label zones green, yellow, and red as already done in the EU and beyond, to identify the presence of community transmission – that is, the virus is spreading in the zone without new importations. Red and yellow zones will be considered equal with regard to the vaccination policy.
   • Classify individuals into four types: people at risk, health workers, connectionists, and travellers.
2. Dependence of the vaccination policy on the epidemiological situation.
   • Red zones. Vaccinate people at risk and health workers to minimise the number of severe cases of Covid-19 and keep hospitals operational. In addition, mobility within, to, and from red zones should be restricted (e.g., seven-day quarantine or two negative tests), as the virus circulation is too high to allow an effective test-and-trace strategy.
   • Green zones. Next to people at risk and health workers, vaccinate travellers and connectionists to reduce the risk of re-importation. In addition, travellers coming from red zones should be required to have been vaccinated (or go on a seven-day quarantine or present two negative tests).

Note that our vaccination policy is in line with the current consensus for red zones but introduces a new, important element for green zones.

Main goal: reduce the number of severe Covid-19 cases

Given that the population at risk is large, alternative vaccination policies need to be explored to protect larger parts of the population more quickly.

Our vaccination plan is intended to minimise the number of severe cases of Covid-19 and thus also the impact on the economy and the health system. By decreasing the probability of re-importation into green zones – where community transmission is close to zero – the likelihood that a person is infected within a green zone equally decreases, and so does the expected number of total infections. More importantly, our policy reduces the risk of contracting Covid-19 in green zones for all its inhabitants, vaccinated or not. We shall now explain the reasoning in more detail.

Our vaccination plan is intended to minimise the number of severe cases of Covid-19 and thus also the impact on the economy and the health system

First, consider a vaccination policy which is not paired with strict travel restrictions and thus focuses fully on (A). Without a vaccine, an individual’s probability of contracting Covid-19 in a green zone (p) is smaller than that in a red zone (q). Vaccinating them will certainly reduce their chances of being ill, but not completely as vaccines are never 100% effective.

For instance, the flu vaccine has reduced the risk of contamination by 44% on average between 2009 and 2018 according to the CDC [7]. Thus, the probability of getting infected proportionally decreases for both, individuals in green zones ((1-e)*p) and in red zones ((1-e)*q). The minimum efficacy required by the FDA to license a Covid-19 vaccine is 50% [8].

Our policy reduces the risk of contracting Covid-19 in green zones for all its inhabitants, vaccinated or not

Second, consider our vaccination policy, where zoning is in place. Again, an individual’s probability of contracting Covid-19 in a green zone (p’) is smaller than that in a red zone (q’). Mobility restrictions reduce the probability of infection most notably in green zones. Reducing the mobility to, from and within red zones reduces the virus re-importation to green zones, and thus the probability of infection in a green zone markedly decreases (p’ ≪ p) [9].

However, the priority on vaccination is now shared between four types of key individuals (people at risk, health workers, connectionists and travellers) and, as such, an individual’s vaccine may be delayed. But as long as the likelihood of infection of someone waiting for the vaccine (in a protected green zone) is smaller than that of a vaccinated individual (without zoning), the former faces a lower risk (p’ < (1-e)*p).

Last, let us explain why the latter comparison likely holds. Reducing the mobility flows from red to green zones to a fraction (X), will entail a similar reduction of the number of re-importations. As the virus then expands following an exponential pattern, the decrease in virus circulation in green zones will be more important than that. Thus, an individual’s likelihood of infection in a protected green zone is proportionally smaller than without zoning (p’ < p*X). Consequently, reducing the mobility by a larger share than the efficacy of the vaccine (X < 1-e) will decrease everyone’s probability of infection – even those who are still waiting for vaccination. That is, as soon as the mobility restrictions outweigh the vaccine efficacy.

So far, we have argued that zoning protects all inhabitants of green zones. Now suppose that some travellers and connectionists are, in addition, vaccinated. On the one hand, vaccinating travellers will further reduce the risk of re-importing the virus to the zone [10]. On the other hand, vaccinating connectionists reduces the spread of the virus within the zone.

To summarise, the zoning policy is not only beneficial collectively, but also from the viewpoint of every individual. Further, as green zones will be much less likely to witness a resurgence of the virus, other health complications (e.g., rescheduling of routine treatments, psychological impact), and social and economic hardship will be reduced. Allowing green zones to return to economic and social activity is essential to saving social cohesion and ensuring economic stability.

Implementation

For the successful implementation of our proposal, several important points need to be deliberated and clarified in the months to come.

Zoning and travel restrictions

Zoning has been implemented in many countries, with Spain and France being the first European nations to adopt this strategy [11]. It is thus natural, and politically acceptable, to use the current zoning as a basis for the vaccination policy. As already argued before, a vaccination policy that omits the mobility restrictions from red zones to green zones would be considerably less efficient.

Individuals with priority

To establish the priority for vaccination, objective criteria need to be set in order to define people as (1) at risk, (2) health workers, (3) connectionists, and (4) travellers. While the definition of the first two categories is largely agreed upon already, that of the latter two requires careful consideration. Who is classified as a connectionist or as a traveller needs to be defined based on observable information, and in a way that is socially acceptable. In particular, this entails that, although definitions may vary from zone to zone, a standardised logic must prevail.

• (1) The population at risk due to age, medical pre-conditions or severe precarity may be too large to be vaccinated immediately as it comprises around 25% in developed countries [12]. As the initial number of doses per capita in the EU is estimated to be around 6%, it is crucial to find narrow criteria that identify those who are at highest risk.
• (2) Health workers play a key role in the implementation of the vaccination policy as they prescribe and provide the vaccines to their patients. Their adherence to the policy proposal is thus of major importance [13]. As such, health workers should take a preponderant role in the discussion in the upcoming months, namely with regard to the definition of ‘people at risk’ and ‘connectionists’, and with regard to mandatory versus optional vaccination.
• (3) Regarding connectionists, three factors should be taken into consideration, an individual’s job, their place of work, and the efficacy of public health measures to protect them from contracting and passing on the virus. For example, a barman in an outdoor venue may not be considered a connectionist, whereas he would be considered as such if the venue was indoors, since the virus is known to transmit more easily indoors. Similarly, a concierge in a theatre may not be considered a connectionist as it turns out that public health measures such as the wearing of masks is adhered to in such venues. On the other hand, a concierge in venues where public health measures are poorly observed should be considered a connectionist.
• (4) With regard to travellers we propose to build on definitions established during lockdown. Initially, those professionals for whom travel is essential should be prioritised (e.g., lorry drivers, people working in a different zone whose presence is necessary) along with imperative personal reasons (such as illness of close relatives or under-age children). In a second step, the traveller category could be expanded based on applications by individuals or their employers.

Once criteria are defined, a detailed mapping of these populations should be conducted. France already published an independently conducted report on priorities for vaccination [12]. (Out of a population of 67M, 20M were deemed at risk due to age (above 65) or medical pre-conditions or severe precarity, 1.8M are health workers, and 5M could be considered as connectionists, defined as people ‘in contact with the population’, ‘working in confined places’ or ‘living in confined conditions’.)

Spain could reproduce the exercise taking advantage of some of its powerful survey tools: the Encuesta de Población Activa, a population survey conducted every quarter that gathers high-quality, segmented information on occupations at the province level. Along with other demographic tools, its fieldwork and data output could be used to estimate vaccination needs across provinces.

Attitudes towards vaccination

In 2019, the WHO named vaccine hesitancy as one of the top ten global health threats, which reflects the worries about under-vaccination and vaccine refusal in many countries across the world [14]. A recent study about vaccine hesitancy in 149 countries from 2015-2019 found low levels of vaccine confidence in Europe in particular [15].

Prioritising the vaccination of connectionists and travellers overcomes several implementation burdens. By leveraging the concept of ring vaccination – targeting those who are most likely to be infected – we can help reduce the spread of the virus despite limited vaccine doses and potential reluctance of vaccine uptake.

A vaccination policy that accounts for the varying epidemiological situations of zones could be critical to achieve lower numbers of severe Covid-19 cases

Vaccination is only required for people with certain characteristics (i.e., connectionists and travellers). Thus, the controversial and politically sensitive issue of mandatory vaccination is replaced by a conditional obligation. This is particularly important as research shows that making vaccination mandatory can be polarising and in fact reduce uptake [16].

Non-medical public health measures and communication

As vaccination will reduce but not remove the risk of contamination, adhering to social distancing and other public health measures in place is important until vaccination is massively distributed. Otherwise, a too quick return to normality could endanger the benefits of vaccination.

Finally, as has become clear throughout the pandemic, the importance of clear and timely communication cannot be overstated. Being frank about unknowns, setting a timeline for implementation, and explaining the decision-making process and the frequency of policy reviews are all paramount for public adherence and support.

International coordination and local realities

A vaccination policy that accounts for the varying epidemiological situations of zones could be critical to achieve lower numbers of severe Covid-19 cases and thus a quicker return to normality. The question of how vaccines should be distributed within zones complements the question of international coordination to ensure a fair and efficient distribution.

To achieve a coordinated and effective vaccination strategy, the realities of different countries need to be taken into account (e.g., different attitudes towards vaccination, or the fact that travel restrictions are easier to control for an island-state compared to a continental European country). The coming months are critical to address the above-mentioned implementation variables.

More broadly, opening the discussion on the fairness of vaccine distribution in light of the varying ex-ante characteristics of individuals, regions, countries, and continents is important. The mere fixing of quotas of vaccination doses per capita may be too simplistic for the exceptional moment we are currently in. Are we ready to consider a vaccination deployment that is dependent on a zone’s social characteristics (e.g., density, precarity, average age), its centrality, or even its economic importance?

Authors’ note. We are thankful to Jorge Galindo and Toni Roldan for their insight and support. A French version of this text was previously published by Terra Nova; concurrently a shorter version was published by VoxEU — the policy portal of the Centre for Economic Policy Research.

References

• [1] E Ezekiel, et al. (2020), An ethical framework for global vaccine allocation, Science Vol. 369, Issue 6509, pp. 1309-1312; and Kelland, K (2020), How can the world ensure a fair distribution of Covid-19 vaccines?, World Economic Forum.
• [2] A Babus, S Das and S Lee (2020), The optimal allocation of Covid-19 vaccines, Covid Economics, Issue 44.
• [3] A more gradual scale is in place in most countries. The EU, for instance, uses three colours (green, yellow and red). This further distinction, however, does not conflict with our proposal which we prefer to present in the simplest framework.
• [4] Vaccins contre le SARS-CoV-2: Une stratégie de vaccination, CARE – Comité scientifique Covid-19 – Comité Vaccin Covid-19 (July 2020).
• [5] Stratégie de vaccination contre le Covid-19, Haute Autorité de Santé (July 2020).
• [6] Vaccins contre le SARS-CoV-2: Une stratégie de vaccination, CARE – Comité scientifique Covid-19 – Comité Vaccin Covid-19 (July 2020).
• [7] CDC seasonal flu vaccine effectiveness studies (2020).
• [8] U.S. Department of Health and Human Services Food and Drug Administration Center for Biologics Evaluation and Research (2020), Development and licensure of vaccines to prevent Covid-19 - Guidance for Industry, June.
• [9] See, for instance, S Vanderslott and T Marks (2020), Travel restrictions as a disease control measure: Lessons from yellow fever, Global Public Health.
• [10] Restricting mobility to a fraction X and vaccinating a fraction Y of incoming travellers with a vaccine of efficacy e will reduce the number of re-importations to X* (1-e *Y). As an illustration take X = 50%, Y = 80% and e = 90%. The number of re-importations will then drop by 86%.
• [11] M Oliu-Barton, B Pradelski and L Attia (2020), Covid-19 exit strategy: from self-confinement to green zones, EsadeEcPol - Center for Economic Policy & Political Economy, Policy insight No. 6, April.
• [12] Vaccins contre le SARS-CoV-2: Une stratégie de vaccination, CARE – Comité scientifique Covid-19 – Comité Vaccin Covid-19 (July 2020).
• [13] Concerning the vaccination hesitancy of French health workers we refer to the works of P Verger, e.g. Hésitation vaccinale dans la population et chez les professionnels de santé en France, 19 April 2019.
• [14] WHO (2019), Ten threats to global health in 2019.
• [15] A Figueiredo et al. (2020), Mapping global trends in vaccine confidence and investigating barriers to vaccine uptake: a large-scale retrospective temporal modelling study, The Lancet Volume 396, Issue 10255, pp. 898-908.
• [16] S Omer et al. (2019), Mandate vaccination with care, Nature Volume 571, Issue pp. 469-472; and A Gibuilini and S Vanderslott (2019), Is mandatory vaccination the best way to tackle falling rates of childhood immunisation? Oxford Martin School blog.