With coronavirus 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 continents, countries, and regions (Ezekiel et al., 2020; Kelland, 2020)? On the other hand, how should the vaccine be allocated within a given region or zone (Babus et al., 2020)? The first question has received much attention, so we shall focus on the second. How will vaccines be rolled out within a zone to minimise the number of severe cases of COVID-19?
Vaccinating by zones
So far, the discussion on who to vaccinate first has focused on the characteristics of individuals or their environments of interaction. While the importance of this distinction is not questioned, we propose considering another fundamental aspect: the various epidemiological situations. In red zones, the virus circulates actively among the population, whereas in green zones, this is not the case. A more efficient vaccination policy can be implemented by considering the colour of zones, as the epidemiological status of zones is constantly monitored and increasingly well understood.
To illustrate the key insight, let us consider two opposing epidemiological situations: a red zone with a particularly high incidence of the virus, and a green zone where the incidence is close to zero. 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 on travellers would thus build a protecting ring around the green zone.
A vaccination policy proposal
Individuals’ centrality in society
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:
People at risk are individuals with the highest risk of developing severe symptoms in case of infection (e.g. old people, people with pre-existing health conditions).
Health workers are individuals who are close to and connect with people at risk.
Connectionists are individuals who are highly central within a community with respect to profession (e.g. students, bar tenders) and environment of interaction (e.g. indoor, cold and dry air).
Travellers are individuals who connect different communities that otherwise would not be connected (e.g. flight attendants, tourists, business travellers).
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: protecting vaccinated individuals from infection (direct protection) and inhibiting them from passing on the virus to others (indirect protection). Remarkably, vaccinating 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 administrations. By contrast, travellers and connectionists are particularly important for indirect protection. Their vaccination would considerably reduce the risk of re-importation and consequently the likelihood of infection for people in green zones – notably, people at risk.
1. Identification of zones and classification of individuals
Label zones green and red, as is already done in several countries, to identify the presence of community transmission. (Community transmission is present if the virus is spreading in a zone even without new importations.)
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 (dependent on a seven-day quarantine or two negative tests, for example), 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).
This plan is intended to minimise the number of severe cases of COVID-19 and thus the impact on the economy and the health system. For the successful implementation of this plan, each step needs to be carefully executed.
Zoning has been implemented in and across many countries, with France and Spain being the first European nations to adopt the strategy (Oliu-Barton et al. 2020, Oliu-Barton and Pradelski 2020). In most of these countries, the current zoning policy has proven to be politically acceptable and could thus be used as a basis for the vaccination policy. Importantly, travel restrictions between zones need to be voluntarily adhered to or enforced. Otherwise, the distinction between red and green zones becomes a weak policy tool.
Regarding 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 depends on the social distancing and health measures in place and needs to be defined based on observable information. Regarding travellers, to avert over-demand from individuals who wish to travel, one could initially refer to individuals whose travel is essential for work or family (e.g. people living and working in different zones and who cannot work from home).
Prioritising the vaccination of connectionists and travellers would overcome 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. Furthermore, the controversial and politically sensitive issue of mandatory vaccination is replaced by a conditional obligation. Vaccination is required only for people with certain characteristics (i.e. connectionists and travellers).
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 the vaccine is widely distributed; an overly 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 the 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
The question of how vaccines should be distributed within zones complements the question of international coordination to ensure a fair and efficient distribution. 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.
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 an exceptional moment. Are we ready to consider a vaccination deployment that is dependent on a zone’s social characteristics (density, precarity, average age, etc.), its centrality, or even its economic importance?
Authors’ note: A longer version of this column will be published by Terra Nova, which develops the French case more in detail.
Babus, A, S Das and S Lee (2020), “The Optimal Allocation of Covid-19 Vaccines”, Covid Economics 44.