Fairness-based techniques to optimize vaccine allocation among migrants during pandemics: a scoping review

Study populations

An immigrant is someone who chooses to leave their country voluntarily, often in search of better living conditions, economic opportunities, education or family reunification. A refugee is someone who is compelled to leave their country to escape war, persecution or natural disasters, and seeks protection in another country under international law. An asylum seeker is an individual who has applied for refugee status and is awaiting a legal decision on whether they will be recognized as a refugee (UN Refugee Agency, 1951; UN Refugee Agency, 2021; World Health Organization, 2022). In this study, the groups included were collectively represented under the general term “migrants”, encompassing refugees, asylum seekers, and other forcibly displaced persons, reflecting the populations described in the included studies.

Assessment tools

In this study, we systematically investigated articles on the vaccination status of migrants, analyzing the percentage of vaccinated individuals and classifying their characteristics. We also reviewed research methods, outcomes, and findings from relevant studies to propose potential vaccine allocation strategies. To achieve this, we conducted a comprehensive literature review using the expectation, client group, location, impact, professionals, and service (ECLIPSE) framework, along with the PRISMA guidelines and the Joanna Briggs Institute’s Checklist for Qualitative Research (Page et al., 2021; Wildridge & Bell, 2002). The keywords obtained in studies were listed according to the ECLIPSE classification. The location step was eliminated because it was not relevant to our inquiry.

Literature search

While creating the search strategy of this study, the keywords “refugees” and “COVID-19 vaccine” were taken as a basis. At the same time, this base was expanded by including the words migrant, immigrant and asylum seeker.

The following terms were used: (vaccine OR vaccination OR Mass Vaccination OR Immunization OR Mass Immunization OR COVID-19 Vaccines OR COVID-19 Vaccination OR Influenza Vaccines OR Influenza Vaccination) AND (Public Health Emergency OR Public Health Service) AND (Prioritization OR Priority OR Rationing OR Routing OR Health Care Rationing OR Allocation OR Resource Allocation OR Fair allocation OR Equity OR Health Equity OR optimization) AND (Priority populations OR Risk groups OR at risk populations OR Migrants OR Refugees). The publications were obtained from searches made from PubMed, Scopus, Web of Science, Cochrane Library, and Ovid Medliner databases, restricted to articles published in English continuing all the key word between 2000–2022.

After this step, the articles were screened in two steps by two researchers. At each step, the articles selected by the researchers were combined, and duplications were eliminated. A critical evaluation of the quality of the selected articles was conducted by two researchers. This evaluation utilized the parameters outlined in the Joanna Briggs Institute’s Checklist for Qualitative Research (Lockwood, Munn & Porritt, 2015). These parameters provided a robust framework for assessing the reliability and validity of the research findings. The synthesis of the data was performed independently by two researchers, and any discrepancies were resolved through a joint review, with one researcher making the final decision.

The data was systematically extracted and categorized under the following headings: author(s), Year, Title, Country, Sample, Study Design, Objectives, Vaccine(s), Operation (Fairness-Based Techniques), and Result. This structured approach ensured clarity and consistency in organizing the information from the included studies.

Eligibility criteria

While mapping the scope of the research, the inclusion and exclusion criteria were determined by holding bi-weekly meetings with a three-member research group. Publications included in this study addressed at least one of the following criteria within communities of refugees or migrants:

• Access to vaccines or vaccine uptake frequency

• Vaccine hesitancy, including decision-making processes, attitudes or behaviors regarding vaccination

• Vaccine modeling studies targeting these groups

• Discussing vaccine allocation and, if available, optimization approaches

• Focusing on discussions grounded in fairness principles

Publications that did not focus on refugee or migrant groups or did not involve vaccination were excluded from the evaluation.

Data analysis

In the first step, 6,397 publications were identified. After removing duplicates with EndNote and the Systematic Review Accelerator (SRA) De-duplicate tool, and excluding records marked as ineligible by automation tools such as Abstrackr and Rayyan, 5,653 publications remained. In the second step, the title screening yielded 305 articles, which were independently reviewed by two researchers (SS and SA) based on their abstracts. Discrepancies were resolved through consensus. After abstract screening, 60 articles were identified, of which 47 met the inclusion criteria following independent review by two researchers (SS and SA) and were selected for full-text evaluation. Based on the full-text review, ten articles were excluded as they did not address issues of vaccine allocation, while three were excluded as they did not discuss issues of migrants. Among the 47 studies that met the inclusion criteria, 27 were further excluded because they were reviews, viewpoints, reports, quick reviews, or thorough reviews, and one qualitative study was excluded because it collected opinions on migrants’ vaccinations exclusively from healthcare workers in the vaccination field, without directly including migrants. At the end of the literature review, 19 articles were finalized to be included in the study. The review group followed the PRISMA reporting guideline for the reporting of this scoping review (Fig. 1).

Characteristics of included studies

Data on the following topics were taken from each study: study method: quantitative, qualitative, mixed methods; study design: cross-sectional, intervention, modeling; study sample: refugee, immigrant, migrant, and mixed with host population; operation (fairness-based techniques); and results (significance, effect size). Nineteen operational studies out of the 47 total included in the study are displayed in the findings section. The remaining 27 articles are reviews, viewpoints, reports, quick reviews, thorough reviews and scoping reviews, with one being qualitative without directly including migrants. Nineteen articles were found focusing specifically on operational studies examining the fairness-based allocation of vaccines in migrants.

The words migrant and immigrant were observed the most in the population; modeling studies were followed most frequently, and as an outcome, accept(ance) was mentioned more frequently than fairness and equity. COVID-19 was mentioned in two-thirds of the studies (Table 1). Out of the 5,653 appearances in the records, only 14 publications included the term ”fairness”, accounting for just 0.2% of the entire dataset. The term “refugee” appeared in 1.6% of publications, while ”(im)migrant” was found in 2.5%. The terms “allocation” and ”optimal” or “optimization” appeared at similar rates, whereas ”model(ing)” and ”access to health” were found in 3.8% and 12.4% of titles, respectively. The terms “acceptance” and “hesitancy” occurred at comparable rates.

Vaccination outcomes

Table 2 presents the characteristics and findings of both operational studies and review studies that met the inclusion criteria. The vaccinations “COVID-19” and “Other” come in two different varieties. In contrast, only the COVID-19 case was the subject of 35 investigations; 12 studies covered influenza, hepatitis B, measles, tetanus, etc. Three categories were recognized as migrants throughout all the studies: refugees, immigrants and migrants, and asylum seekers. Twelve studies focused on vaccination hesitancy, six examined vaccine access, and 13 examined vaccine uptake. Even though 27 of the studies were reviews, 14 had policy as their conclusion. On the distribution of vaccines among migrants, there are just two modeling studies. Vaccination rate was between 42.7% and 87% (Fig. 2). Most articles identified systematic, scoping, and rapid reviews and found that migrants experienced a higher burden of infection and lower vaccination rates than the host population. These studies also concluded that the desire to be vaccinated was around 70 percent, and reasons for not being vaccinated were listed as the lack of access to health services, health communication barriers (language), lack of support, feelings of being excluded in health interventions compared to the general population and lack of access to information. Under the title of Vaccination Strategy for Migrants, 8.5% of the articles emphasized the prioritization of migrant workers, while only 2.1% focused on the prioritization of elderly migrants. Vaccination campaigns in multiple languages were discussed in 6.3% of the publications. Specific campaigns targeting migrants were highlighted in 14.8% of the studies, and 10.6% addressed vaccination strategies for undocumented migrants.

Figure 2 illustrates vaccination rates reported in multiple studies focusing on refugee and migrant populations. Migrant vaccination rates ranged from 60% to 87%, whereas refugee vaccination rates ranged from 42.7% to 76.0%.

Fairness-based strategies

We defined how frequently factors such as acceptance, accessibility, and hesitancy have been investigated over time in the context of refugee vaccination during pandemics. Notably, acceptance shows a marked increase in recent years, reflecting growing research attention to vaccine uptake challenges. Overall, it underscores the evolving focus on fairness-based strategies in public health research concerning refugees.

Among the 19 operational studies, specific strategies were outlined for defining and improving vaccination approaches for refugees, as presented in Table 3. On the other hand, the idea of fairness varied greatly among studies. While some discussed fairness regarding community involvement and the use of health services, others emphasized the necessity for a just distribution of vaccines. While in some papers, fairness was described in terms of vaccination hesitancy and vaccination, in one study, fairness was explored as a method to protect vulnerable groups concerning the rate of transmission of infection. The case studies underlined the importance of providing refugees with vaccines but made no specific recommendations on implementation (Table 3).

Several studies highlighted community-based and culturally tailored approaches as critical facilitators. Streuli et al. (2021) integrated community engagement at every stage of an innovative vaccine education technology for Somali refugees, ensuring that materials were culturally and linguistically appropriate to address low health literacy and medical mistrust. Similarly, Kowal, Jardine & Bubela (2015) working with community partners, used informal, language-appropriate communication methods and materials, while Allen et al. (2022b) reported an 87% vaccination completion rate in a study involving collaboration with community leaders and social media groups.

Modeling studies provided valuable insights into fairness-aware strategies. One study used a refugee camp setting to develop single-dose and two-dose outbreak control scenarios. The SEAIRD model, which explored optimal vaccination strategies under the practical constraints of limited medical resources, found that outbreak control in challenging environments such as refugee camps also depends on maximum daily vaccination capacity. Another example is Witbooi’s (2021) SEIR model, which integrated local and migrant populations into a single framework to assess migrant dynamics in terms of inflow and outflow. This model also emphasized the necessity of achieving 95% measles vaccination coverage among newborns in each group.

Barriers and facilitators

In our review, we identified several common barriers and facilitators affecting vaccine uptake among migrants. One of the most prominent barriers was uncertainty about legal status, particularly for undocumented migrants, who either could not access healthcare services or avoided them due to fear of potential consequences. Language barriers were another major challenge, limiting access to the healthcare system and making it difficult to understand vaccination-related information. A general lack of trust in government institutions and the healthcare system further discouraged participation in vaccination programs. Insufficient or misleading information about vaccines also contributed to hesitancy. Logistical difficulties, such as long distances to vaccination centers and limited transportation options, were especially common in rural and peri-urban areas. In addition, cultural and religious beliefs were sometimes linked to skepticism or hesitancy toward vaccines.

On the other hand, several facilitators were reported to improve vaccine access and acceptance. Community-based approaches, including outreach through local leaders and community partners, played a key role in building awareness and trust. Providing multilingual information materials and incorporating cultural sensitivity into campaign design—ensuring that both messages and delivery methods respected local norms and values—were associated with higher participation rates.

In some studies, digital health tools were particularly effective; for example, Knights et al. (2021) noted that language obstacles and challenges in establishing trust limited the effectiveness of digital health messaging, while Streuli et al. (2021) successfully addressed these issues through bilingual virtual technology. Other studies used digital health platforms to conduct surveys and simplify data collection, whereas Streuli et al. (2021) combined cultural elements with community engagement in virtual education, further expanding the applicability of such tools. Finally, digital health tools, such as targeted health messages and visual educational resources, were effective in delivering accurate vaccine information and reaching otherwise hard-to-access groups.

Strengths and limitations

Our study was undertaken during the COVID-19 pandemic, which has raised questions about how quickly vaccines should be distributed. One of the study’s limitations is the inability to assess long-term trends in vaccine dissemination, as most included studies focused on short-term or early-stage interventions. The results of each study alone helped understand vaccination. Still, it was difficult to draw firm conclusions and synthesize results due to the variety of methodologies and methods used to measure rates of vaccination, vaccine acceptance and vaccine requests. Our study faced challenges in identifying publications that specifically addressed fairness vaccine allocation or centered discussions on large-scale migrant vaccination initiatives, as vaccine distribution models have not received significant public attention. Another limitation of this study is its reliance on smaller-scale interventions, which constrained its ability to provide a comprehensive definition of fairness in vaccination. Furthermore, significant heterogeneity across studies—in terms of methodology, outcome measures (e.g., vaccine uptake, acceptance or demand), and target populations—posed challenges for synthesis and comparability.

Another notable limitation is the potential publication bias, as most included studies originated from high and middle-income countries. Government-led or community-based strategies in low-income countries may exist but are unpublished in academic sources. Additionally, the restriction of English-language publications may have further limited the geographic and linguistic diversity of the review.

The review also faced challenges in identifying studies that explicitly addressed fairness-based vaccine allocation or large-scale national immunization efforts targeting migrant populations. Most of the studies focused on smaller-scale interventions or community-level strategies, which constrained the analysis and limited the generalizability of findings.

Despite these limitations, the review contributes to the literature by highlighting the need for consistent terminology when studying displaced populations, and by identifying the gap in research focusing specifically on fairness-oriented vaccination strategies for migrants.