The ongoing coronavirus disease 2019 (COVID-19) pandemic has infected over 130 million people globally, resulting in 2,842,325 deaths as of April 4, 2021.1 To achieve a protection threshold in the population, 67% of people would have to develop natural immunity.2 Despite the increased number of infections, this seems difficult to attain, as studies in the United States (US) reported low rates of patients with antibodies to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (< 24%), even after the large wave in the winter.3 Similarly, poor results were reported in the European Union/European Economic Area (EU/EEA) (1.0–8.5%)45 and the Republic of Korea (< 1.0%).67 Thus, it seems that vaccination is necessary to reach the protective threshold.

As of April 2, 2021, 28 vaccine candidates entered phase 3 of clinical trials.8 It is expected that 74% of phase 3 vaccines will be approved.9 Nevertheless, an initial limitation in the supply is expected because of manufacturing issues. The crucial question arising is who gets first access to vaccines when they become available.

During the previous H1N1 influenza pandemic in 2009, many countries (including Republic of Korea) applied step-by-step strategies according to vaccine supply. The Advisory Committee on Immunization Practices (ACIP) in the US has steadily updated guidelines on allocating and targeting vaccines during influenza pandemics.1011 Currently, these principles have informed the ACIP's strategy concerning the COVID-19 vaccination. However, the SARS-CoV-2 is remarkably different from influenza, and new vaccine allocation protocols are necessary.

Unlike the 2009 pandemic, the incidence or severity of COVID-19 infection is relatively low in children and adolescents, and severe morbidity and mortality are prevalent in the older population. Transmission-related risk groups are also difficult to clearly define.1213 Thus, considering the characteristics of COVID-19 known to date, the major organizations and countries, such as the World Health Organization (WHO), US, and United Kingdom (UK), suggest allocating the first batch of COVID-19 vaccines to healthcare personnel and populations at high risk of severe morbidity and mortality, such as older persons and persons with comorbidities.141516 However, the range or ranking of each target population has not yet been specified in most countries, and the inclusion of high-exposure occupations varies between countries. The detailed strategy of each country should be based on its own situations, such as epidemiology, financial status, public acceptance, and availability of vaccine doses.

During the study period, it was not known which vaccines would be approved, although the minimum criteria for approval recommended by the WHO were presented,17 and the priority would vary depending on the characteristics of vaccines to be developed. Nevertheless, at this point, a draft of the preliminary strategy for allocation of the COVID-19 vaccine reflecting the domestic situation was necessary for vaccine introduction. The present study discusses and proposes foundational objects and outlines a framework for the allocation of COVID-19 vaccines in the Republic of Korea.

In the present study, three topics were discussed to create a framework for the allocation and prioritization of COVID-19 vaccination: 1) identifying the objectives of the vaccination strategy, 2) identifying the allocation criteria, and 3) establishing a step-by-step vaccination framework and prioritization strategy based on allocation criteria (Fig. 1). To manage the task, two panels were convened: a core panel and an expert panel. The core panel, consisting of 6 researchers, was the strategic steering group that oversaw the task. The modified Delphi technique was used, where the core panel collected updated data and background evidence, provided a structured questionnaire, hosted online meetings, and gathered expert opinions. The expert panel consisted of 13 relevant experts. This study was conducted from July 23, 2020, to October 31, 2020. Specifically, the survey on the first topic was carried out from August 11, 2020, to August 21, 2020; on the second topic, from August 21, 2020, to September 21, 2020; and, on the last topic, from September 21, 2020 to October 31, 2020 based on the previous surveys. During this period, the vaccination strategies of several organizations and countries were being updated.181920212223 By referencing these standards and with an additional systematic review,152425 the panels devised a strategy suitable for the domestic situation. The process was as follows:

First, the core panels reviewed previous pandemic and vaccine strategies of major organizations and countries, assessed the progress of vaccine development, and prepared background evidence reports for each topic. Second, the standards were selected from representative frameworks and modified for the Korean situation. The core panel created and provided a structured questionnaire using the modified evidence. Third, expert opinions were gathered through several rounds of the modified Delphi technique. Fourth, the framework was completed through expert consensus and revision by the core panel. As the time period required to obtain enough vaccines was not known, the researchers considered the initial supply of vaccine to be tightly constrained, enough for only approximately 3–5% of the Korean population.1826 Since vaccine supply would be phased incrementally with increasing supply, the researchers planned to list target groups according to how the vaccine would be secured in approximately 5 phases.

This study proposed pandemic frameworks for COVID-19 vaccine allocation by organizing a Delphi survey of experts from the fields of vaccination, infectious disease, and public health in the Republic of Korea. The results of this survey are in line with those of previous reports that focused on initially reducing mortality and protecting the health system.18192330 Reduction of transmission was also a fundamental objective, but this approach was difficult to apply initially for the following reasons. First, any substantial impact of vaccination on reducing transmission would require a mass of individuals to be vaccinated. In the early phase, there would not be a sufficient amount of vaccines available for this effective transmission-focused strategy. Moreover, ongoing vaccine trials have not been designed to estimate the impact on transmission, and evidence of such an impact might not be available for some time after approval. Furthermore, considering the lack of data on transmission risk groups, it is important to focus on a reasonable group that will clearly benefit from vaccination at the start of the vaccination program.

To achieve the goal of reducing mortality and protecting the health system, the WHO and COVAX facilities included the following groups as reasonable targets for Tier 1: frontline workers in health and social care settings, people over the age of 65 years, and people who have underlying comorbidities that put them at higher risk of death.1430 Similar priority groups were proposed in Europe, the UK, Canada, and Australia.31323334 The National Academies of Sciences, Engineering, and Medicine (NASEM) and Joint Committee on Vaccination and Immunisation (JCVI) also suggested similar concepts but especially emphasized high-risk individuals among health and social care workers (in terms of risk of transmission to vulnerable persons and acquiring infection) and older adults in congregate settings.1834 Thus, the possible priority groups presented in this study are similar to those prioritized by major countries or institutions. Among these priority groups, people with comorbid conditions were divided into two groups (significant and moderate) in this study, as they accounted for a quarter of the total population. However, the evidence used to classify them is still insufficient. In the framework suggested by the NASEM, those with two or more high-risk comorbidities were classified as having significant risk, while those with only one were classified as having moderate risk.18 In the present study, significant- and moderate-risk comorbidities were temporarily classified according to the level of evidence presented by the Centers for Disease Control.35 This classification may change continuously as data are collected, and the classification itself may be meaningless if sufficient amounts of vaccine doses are secured at once.

In this study, the ranking of pregnant women was not discussed. Because pregnancy is one of the possible conditions that puts women at high risk,35 the ranking needs to be reviewed as soon as the vaccine efficacy and safety data are collected. In addition, the ranking of children and adolescents was low because of the low mortality rate in this group.36 Although data are still limited, this group could be meaningful as a transmission source, as with influenza, and the vaccination of this group could be significant in terms of resumption of education and reducing outbreaks in the population.37 The ranking of this group will be reviewed as soon as more information is collected.

The framework presented in this study was based on the evidence and epidemiological situation as of October 31, 2020. There was a lack of certainty about the characteristics of COVID-19 vaccines that could become available in the Republic of Korea, and gaps remain in the scientific knowledge of the virus and disease. Because a range of uncertain factors may affect the implementation of the framework, these results should be interpreted cautiously, and it is necessary to consider various scenarios in advance. First, the vaccination strategy against COVID-19 will ultimately be guided by the available vaccines and the outcomes against which each vaccine will provide protection. If the efficacy is inferior in older adults or people with comorbidities, changes in the framework of the priority target group should be considered. It would be helpful to perform mathematical modeling of whether individuals in the priority groups in the framework should still be offered vaccination if the vaccine is less efficacious for these groups. The actual efficacy is also affected by how well people adhere to the basic non-pharmaceutical interventions; therefore, appropriate public health messages and education emphasizing such interventions are necessary. Another important issue is vaccine safety. Knowledge about vaccine safety from clinical trials is limited. Monitoring the side effects and adjusting the allocation framework are necessary steps to minimize safety concerns. Transparent communication with the public about the risks and benefits of vaccines is crucial. Before moving on to the next step in ranking, it would be necessary to make the best effort to vaccinate all prioritized populations. There may also be a scenario in which several vaccines with different characteristics are concomitantly approved. For the best results, available information should be gathered to determine the optimal vaccine for each target group. When multiple vaccines are used, the importance of monitoring efficacy and safety must be re-emphasized. The severity of the outbreak will also influence vaccine allocation. If the pandemic is severe and a substantial number of people are infected, the maintenance of social infrastructure may become a more important objective, and, in this case, critical infrastructure workers outside the health sector as well as all healthcare workers might take priority. In addition, the route and frequency of administration; stability in storage and transportation for each vaccine; and social, economic, and legal aspects may also affect the implementation of the framework.

During the study period, data on the characteristics of each vaccine were scarce. Since November 2020, phase 3 results of representative vaccine candidates were released,383940 and some vaccines were approved and widely administered. The recently published results of Phase 3 clinical trials, which focused on the prevention of symptomatic COVID-19 infection, showed substantially higher efficacy than the minimal recommendation of the WHO,17 with some vaccines reportedly having more than 90% efficacy. However, vaccine efficacy is considerably decreased depending on the variant strains, highlighting the need for monitoring of circulating strains at the time of administration. Some vaccines showed similar efficacy in older adults,3839 while others have not yet been analyzed among older adults.4142 Persons with comorbidities were usually included, but immunocompromised or pregnant women were not included in most studies, and there were scarce data on children. Vaccination plans and strategies need to be adapted as more information becomes available. For this, high-quality surveillance and adequate modeling capacities should be emphasized.

This study presented a framework for allocation and distribution decisions related to scarce SARS-CoV-2 vaccines. While reaching consensus, the members of the expert panel used information available as of October 31, 2020, to identify priority groups. Flexibility in adapting strategies is essential, especially as new information is emerging almost every day, which could influence our assessment of priority groups. Although the final decision on vaccine allocation must also take into account national policies on the type and amount of vaccine supply, public acceptability, epidemiologic consideration, equity, and other factors, this survey provides much needed insight into the decision-making process for vaccine allocation at the national level. Furthermore, the process presented here may assist policymakers in other countries by providing guidance on how to allocate the COVID-19 vaccine, at least in the initial stages of deployment.