Spotted on Terra Nova.
By Miquel Oliu-Barton and Bary Pradelski, associate professor at Paris-Dauphine University
and Bary Pradelski, a research fellow at the CNRS and an associate member of the Oxford-Man Institute
The COVID-19 vaccination policy should be tailored to the prevalence of the virus in a given area, that is, a predefined geographic region. In red zones, high-risk individuals and healthcare workers should be vaccinated first in order to reduce the number of deaths and enable the hospital system to continue functioning properly.
In green zones, on the other hand, the goal would be to reduce the risk of reimportation of the virus and keep its circulation at a level close to zero: therefore, travelers moving between zones and individuals at the center of contact networks should be prioritized there. Indeed, there is no community transmission in green zones. Many countries have imposed travel restrictions between green and red zones within their territories and with other countries. The effectiveness of the policy outlined here depends on such restrictions.
The likelihood of developing a coronavirus vaccine raises the question of how it will be distributed. Two aspects must be taken into account. On the one hand, how should vaccine doses be allocated among continents, countries, and regions? On the other hand, how should they be allocated within a single region or area? So far, the first question has received the most attention. Let’s focus on the second. Within a given area, who should be prioritized for vaccination to minimize the number of severe cases of COVID-19?
VACCINATE BY AREA
Until now, when considering vaccination priorities, the focus has been on an individual’s personal characteristics or their social network. This is obviously an important issue, but we propose taking another fundamental aspect into account: the epidemiological status of each zone. These statuses are constantly monitored and are being better understood. In red zones, the virus is actively circulating within the population. This is not the case in green zones.¹ To be most effective, vaccination policy must take into account not only individual data but also the color-coded zones. Its effectiveness will also depend on travel restrictions between zones to significantly reduce the risk of reimporting the virus into green zones.
During the pandemic, the distinction between red and green zones is a powerful tool. First, because it is fair—provided that the classification criteria are objective and predefined. Second, because it provides a framework for flexible and understandable policies—provided that the status of the zones is clearly and regularly communicated. Finally, as used by several countries, notably France, where zones are identified at the departmental level, this distinction has proven to be politically acceptable. However, for them to be effective, the various public health measures implemented in each of these geographic areas must be supplemented by restrictions on movement between red and green zones, as well as within each zone. This is all the more important in green zones, as their status («the virus is not currently circulating here») would lose all meaning if travel from red zones to green zones were not restricted.
To illustrate the central idea of a color-based vaccination policy, let’s consider two contrasting epidemiological situations: a red zone with a high incidence of the virus and a green zone where the incidence is close to zero. In the first, priority should be given to at-risk populations in order to limit, in the short term, the number of severe cases of COVID-19. In the second, priority should be given to travelers arriving or returning
1 A more granular scale is used in most countries, particularly in France and within the European Union. The model is simplified here but is consistent with the observed reality of a red zone, which is intended to reduce the risk of reimportation of the virus. Requiring travelers to be vaccinated would thus help create a protective ring around the green zone.
Figure 1 – The Different Epidemiological Situations in French Departments as of September 24, 2020
PROPOSAL
CATEGORIES OF INDIVIDUALS
The coronavirus spreads through close physical contact. The likelihood of transmission and the risk of developing a severe form of COVID-19 vary from person to person. Finally, the network of physical proximity—which allows us to study the spread of the virus—has a hierarchical structure: from households to communities, cities, countries, and even continents.
Four categories of key individuals emerge from these findings:
(1) At-risk individuals who are most likely to develop severe symptoms if infected (older adults, people with underlying medical conditions, people living in extremely precarious circumstances); ;
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(2) The healthcare professional who is close to at-risk individuals and connects them with one another;
(3) The connectionist who plays a central role in the area due to their activities (students, bartenders, etc.) or the environment in which their interactions take place (confined space, cold and dry air, etc.); ;
(4) The flight attendant who connects the different groups (flight attendants, tourists, business travelers, etc.).
Figure 2 – The four types of key individuals in the vaccination policy presented here.
DIRECT AND INDIRECT EFFECTS OF VACCINATION
Our proposal takes into account both the heterogeneity of regions and that of individuals. Since time and resources are limited, two complementary benefits of vaccination must be pursued: (A) protecting vaccinated individuals from infection (direct protection) and (B) preventing them from transmitting the virus to others (indirect protection).
Healthcare workers are both highly exposed to the virus and in contact with at-risk individuals: vaccinating them therefore provides dual protection—both direct and indirect. In fact, along with at-risk individuals, they are obvious candidates for direct protection, which
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regardless of the epidemiological situation in the area. There is, in fact, a consensus among government agencies that these groups should be prioritized. Travelers and those who come into contact with them, on the other hand, fall under the category of indirect protection. Their vaccination is nonetheless essential, as it would significantly reduce the risk of the virus being reintroduced into green zones.
While it seems feasible to take into account the difference between (A) and (B) when defining a vaccination policy, this is not the usual framework for such considerations. In France, for example, the concept of indirect protection is mentioned in the reports of the Scientific Council² and the High Scientific Authority³. However, only (A) is taken into account when prioritizing vaccinations, perhaps due to the lack of a clear zoning strategy. Without mobility restrictions, the entire French territory would quickly become a single zone: a red zone as long as the virus is actively circulating anywhere in the country. Green zones would then be exposed to an increased risk of the virus being reimported, even though mobility restrictions and taking (B) into account would make it possible to avoid this.
A ZONE-BASED VACCINATION POLICY
Several steps are required:
1. Identify areas and categories of individuals
● As is done in several countries, identify potential community transmission by designating areas as green or red. If the virus spreads in an area without new imported cases, it indicates that community transmission is occurring.
● Divide individuals into four categories: at-risk individuals, healthcare workers, people who spend a lot of time online, and travelers.
2. Establish a link between vaccination policy and the epidemiological situation
2 SARS-CoV-2 Vaccines: A Vaccination Strategy, CARE – COVID-19 Scientific Committee – COVID-19 Vaccine Committee (July 2020).
3 COVID-19 Vaccination Strategy, French National Authority for Health (July 2020).
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• Red zones. Vaccinate at-risk individuals and healthcare workers to minimize the number of severe COVID-19 cases and enable the hospital system to continue functioning. Furthermore, since the virus is circulating too widely for an effective test-and-trace strategy to work, restrict travel within, to, or from red zones—for example, by requiring a seven-day quarantine or two negative test results.
• Green zones. In addition to at-risk individuals and healthcare workers, vaccinate travelers and those with close contacts to reduce the risk of reimportation. Furthermore, travelers arriving from red zones should have been vaccinated, undergo a seven-day quarantine, or present two negative test results.
Please note: This vaccination policy reflects the current consensus for red zones but introduces a new and important element for green zones.
MAIN OBJECTIVE: TO REDUCE THE NUMBER OF SEVERE CASES OF COVID-19
Since the at-risk population is potentially large (for example, in France, according to a recent estimate⁴, more than 20 million people are at risk due to their age or health status), it is essential to rethink standard vaccination strategies in order to protect a larger portion of the population.
Our region-based vaccination policy aims to minimize the number of severe cases of COVID-19 and, at the same time, limit the impact of this pandemic on the economy and the healthcare system. To achieve this, it is crucial to reduce the likelihood of the virus being reintroduced into green zones, where community transmission is close to zero. Doing so will also reduce the likelihood that a person will become infected there, as well as the projected total number of infections.
4 SARS-CoV-2 Vaccines: A Vaccination Strategy, CARE – COVID-19 Scientific Committee – COVID-19 Vaccine Committee (July 2020).
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Let’s now explain in detail why the proposed policy reduces the risk of contracting COVID-19 in green zones for all residents, whether vaccinated or not. First, let’s consider a vaccination policy based solely on (A), that is, not combined with strict mobility restrictions. Without a vaccine, the probability that an individual will contract COVID-19 is p in a green zone and q in a red zone, where q is greater than p. While the vaccine certainly reduces the risk of illness, it does not eliminate it entirely, as vaccines are never 100% effective. For example, according to the U.S. Centers for Disease Control and Prevention (CDC)⁵, the flu vaccine reduced the risk of infection by 44¹/³ on average between 2009 and 2018. If e denotes the vaccine’s efficacy, the probability of an individual becoming infected is pe in the green zone and qin the red zone. The U.S. Food and Drug Administration (FDA) requires a minimum efficacy of 50%6 to approve the COVID-19 vaccine.
Next, let’s consider our vaccination policy in conjunction with a zoning policy. The probability that an individual will contract COVID-19 is p’ in a green zone and q’ in a red zone. Mobility restrictions may mean that q’ is lower than q (i.e., the risk of infection is lower in red zones under a zoning policy), but we will assume that these two figures are in fact essentially equal. In green zones, on the other hand, reducing mobility to, from, and within red zones reduces the reimportation of the virus more significantly: p’ is therefore significantly lower than p7. However, four categories of individuals now share priority for vaccination: at-risk individuals, healthcare workers, network users, and travelers. As a result, the vaccination of at-risk individuals may be delayed. Nevertheless, everyone will be better protected as long as p’ remains lower than pe, even those who haven't been vaccinated.
Finally, let's examine why it is likely that p’ will remain less than pe. For the record, mobility restrictions are crucial in zoning policy. Indeed, reducing mobility
5 ‘CDC Seasonal Flu Vaccine Effectiveness Studies’ (2020).
6 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 2020).
7 See, for example, S. Vanderslott and T. Marks (2020), ‘Travel restrictions as a disease control measure: Lessons from yellow fever,’ *Global Public Health*.
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A reduction of X in the number of people traveling from red zones to green zones will lead to a proportional reduction in the number of re-importations of the virus. Since the virus spreads exponentially, the decline in its circulation will be even greater. Consequently, p’ will be less than pX. All residents of the green zones will then be better protected (even without a vaccine) than in a scenario with a vaccine but without zoning, provided that X is less than e. In other words, as long as the effects of mobility restrictions outweigh the vaccine’s effectiveness.
So far, we have shown how zoning helps protect all residents of green zones. Let’s now add vaccination—even partial vaccination—of travelers and commuters. On the one hand, vaccinating travelers will further reduce the risk of the virus being reintroduced into Zone 8. On the other hand, vaccinating commuters reduces the spread of the virus within the zone.
In short, this zone-based vaccination policy benefits not only the community but also each individual. Furthermore, reducing the likelihood of a resurgence of the virus in green zones mitigates other health complications (such as the postponement of routine treatments and psychological impacts) as well as economic and social hardships. Allowing green zones to return to normal levels of activity is essential for preserving social cohesion and ensuring economic stability.
8 If, in addition to mobility restrictions X, a proportion v of travelers is vaccinated, the number of reimports will be multiplied by X(1-v*e). Thus, if, for example, X = e = v = 50%, reimports will decrease by 62.5%.
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Figure 3 – Restricting travel from red zones reduces the risk of contracting COVID-19 in green zones. When travel restrictions are more effective than the vaccine, everyone in green zones is better protected, including those who are unvaccinated.
IMPLEMENTATION
The successful implementation of our proposal will require us to discuss and clarify several important issues in the coming months.
ZONING AND TRAVEL RESTRICTIONS
Several countries, primarily France and Spain, have implemented a zoning strategy.⁹ Using the current zoning system as the basis for vaccination policy therefore seems natural and politically acceptable. Nevertheless, as we have already shown, without restrictions on movement from red zones to green zones, this vaccination policy will be far less effective.
9 M. Oliu-Barton, B. Pradelski, and L. Attia (2020), “Covid-19 Exit Strategy: From Self-Confinement to Green Zones,” ESADE—Center for Economic Policy & Political Economy, Policy Insight No. 6, April.
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Figure 4 – Implementation of our policy proposal in France. For simplicity, all the alert zones shown in Figure 1 have been marked in red; the others are marked in green.
PRIORITY INDIVIDUALS
To establish a priority order for vaccinations, it is necessary to set objective criteria for classifying individuals as (1) at-risk, (2) healthcare workers, (3) connectionists, or (4) travelers. While there is broad consensus on the definitions of the first two categories, those of the last two require special attention. To determine who is considered a contact or a traveler, one must rely on objective information and a socially acceptable methodology. The same logic must apply to all areas, even though local variations in definitions may occur.
(1) There may be too many people at risk due to their age, medical history, or severe financial hardship to vaccinate them all right away. It is therefore crucial not only to establish more selective criteria for identifying those at highest risk, but also to target other groups of people whom vaccination will indirectly protect.
(2) Healthcare workers play a key role in implementing the vaccination policy: they prescribe and administer vaccines to their patients. It is therefore
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It is essential that they support the proposed policy. As such, they should play a leading role in the discussions over the coming months—not only regarding the definition of «at-risk individuals» and «connectionists,» but also regarding whether vaccination should be mandatory or voluntary.
(3) To define a “connectionist,” three factors must be taken into account: their job, their workplace, and the effectiveness of public health measures aimed at protecting them from contracting and transmitting the virus. Since the virus spreads more easily in enclosed spaces, a bartender working outdoors might not be considered a “connectionist,” whereas they would be if they worked indoors. Similarly, if public health measures such as mask-wearing are followed, a theater usher might not be considered a “connectionist,” but would be considered one if these measures are only partially followed.
(4) For travelers, we propose using the definitions established during the lockdown. Initially, priority should be given to professionals whose travel is essential (truck drivers, people working in a different area whose presence is necessary) and to those with personal obligations (illness of a family member or minor). In a second phase, the definition of travelers can be expanded based on requests from individuals or their employers.
Some figures. France has a population of 67 million. A recent report on the vaccination strategy¹⁰ estimates that the at-risk population—due to age (over 65), pre-existing medical conditions, or severe economic hardship—exceeds 20 million people. The number of healthcare workers is estimated at 1.8 million, and the number of “connexionists”¹¹ at 5 million.
10 SARS-CoV-2 Vaccines: A Vaccination Strategy, CARE – COVID-19 Scientific Committee – COVID-19 Vaccine Committee (July 2020).
11 The term “connectionist” is not used, but the report estimates that 5 million people are in contact with the general public, working or living in confined spaces.
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POSITIONS ON VACCINATION
In 2019, the WHO ranked vaccine hesitancy among the top ten global health threats. This clearly reflects concerns about under-vaccination and vaccine refusal in many countries around the world12. A recent report13 examined vaccine hesitancy in 149 countries between 2015 and 2019 and found, particularly in Europe, a low level of trust in vaccines.
Prioritizing the vaccination of high-contact individuals and travelers helps overcome several implementation challenges. For example, using the concept of ring vaccination—which targets those most likely to become infected—helps reduce the spread of the virus despite limited vaccine supplies and potential reluctance toward vaccination.
In our model, vaccination is required only of people with certain characteristics (in this case, commuters and travelers). Consequently, the controversial and politically sensitive issue of mandatory vaccination is replaced by a principle of conditional obligation: «If you want to travel or continue your work, you must get vaccinated.» Research has indeed shown that a vaccination mandate can polarize society and ultimately reduce public participation.¹⁴.
NON-MEDICAL PUBLIC HEALTH MEASURES AND COMMUNICATION
Vaccination will reduce but not eliminate the risk of infection. It is therefore essential to continue enforcing social distancing and other public health measures in place until widespread vaccination coverage is achieved. A return to normal too soon could jeopardize the benefits of this policy.
12 WHO (2019), ‘Ten threats to global health in 2019.’.
13 A Figueiredo et al. (2020), ‘Mapping global trends in vaccine confidence and investigating barriers to vaccine uptake: a large-scale retrospective temporal modeling study,’ *The Lancet*, Volume 396, Issue 10255, pp. 898–908.
14 S. Omer et al. (2019), ‘Mandate vaccination with care,’ *Nature*, Vol. 571, pp. 469–472; and A. Gibuilini and S. Vanderslott (2019), ‘Is mandatory vaccination the best way to tackle falling rates of childhood immunization?’ Oxford Martin School blog.
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Finally, the importance of clear and timely communication cannot be overstated. As we have seen throughout the pandemic, to gain public buy-in and support, it is essential to be candid about what we do not know, to establish a timeline for implementation, and to explain the decision-making process and the frequency of policy reviews.
INTERNATIONAL COORDINATION AND LOCAL REALITIES
To achieve a low number of severe COVID-19 cases and a rapid return to normalcy, the vaccination strategy will need to take into account the varying epidemiological situations in different regions. Two complementary questions must be addressed: how to distribute vaccines within these regions, and what kind of international coordination is needed to ensure equitable and effective distribution. Achieving a coordinated and effective vaccination strategy requires taking into account the diverse realities of different countries (for example, varying attitudes toward vaccination or the fact that travel restrictions are easier to enforce for an island nation than for a country in continental Europe). The coming months will be crucial for addressing these implementation variables.
More generally, it is important to have a discussion about the equitable distribution of vaccines in light of the various pre-existing characteristics of individuals, regions, countries, and continents. Setting vaccine dose quotas for each country based on population size may be too simplistic given the exceptional circumstances we are currently facing. Are we prepared to accept a vaccination rollout that would depend on a region’s social characteristics (for example, population density, poverty, average age), its centrality, or even its economic importance?
Note. The authors would like to thank Thierry Pech and Mélanie Heard for their comments and support. A shorter version of this paper will be published simultaneously by VoxEU—the policy portal of the Center for Economic Policy Research (CEPR).
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