Defining the Determinants of Vaccine Uptake and Undervaccination in Migrant Populations in Europe to Improve Routine and COVID-19 Vaccine Uptake: A Systematic Review

"COVID-19 has presented new opportunities to engage more effectively with migrants and other marginalised groups around vaccination,...and future research must focus on identifying novel and participatory approaches that facilitate uptake in specific migrant groups and can be embedded in vaccination programmes."

Some migrant populations are known to be at risk of underimmunisation and have been involved in outbreaks of vaccine-preventable diseases in the European Union (EU) and European Economic Area (EEA). In an effort to improve uptake and coverage of routine and COVID-19 vaccination in diverse migrant populations in the EU and EEA, the systematic review identifies (i) barriers and facilitators to vaccine uptake in migrants (categorised using the 5A taxonomy: access, affordability, awareness, acceptance, and activation) and (ii) sociodemographic determinants of undervaccination. The goal is to inform the development of evidence-based interventions to improve vaccine equity.

The researchers searched MEDLINE, CINAHL, and PsycINFO from 2000 to 2021 for primary research, with no restrictions on language. They screened 5,259 data sources, with 67 studies included from 16 countries, representing 366,529 migrants. Forty-three studies addressed barriers to or facilitators of vaccine uptake. Unique subthemes relating to barriers (n=20) and facilitators (n=18) to uptake were defined and are summarised in panel 2 in the paper.

In short, the studies identified multiple access barriers - including language, literacy, and communication barriers, practical and legal barriers to accessing and delivering vaccination services, and service barriers such as lack of specific guidelines and knowledge of healthcare professionals (HCPs) - for key vaccines including measles-mumps-rubella (MMR), diphtheria-pertussis-tetanus (DPT), human papillomavirus (HPV), influenza, polio, and COVID-19 vaccines. For example, some Moroccan, Turkish, and Somali populations said they preferred oral information, and written formats were not appropriate. In the absence of translated or accessible information, migrants also turned to alternative and unregulated sources, such as Google, social media, friends, and family. Staff shortages, including of bilingual HCPs, interpreters, and cultural mediators, were among the barriers, particularly in camps and reception settings.

There were several access-related facilitators of vaccine uptake, including cultural competence, integration, and engagement. Cultural competence of HCPs and migrant-sensitive services and policies facilitated uptake. For example, in Sweden, all newly arrived migrant children are invited to meet with the school nurse to determine health and vaccination needs, helping to establish trust early.

With regard to acceptance, barriers were mostly reported in eastern European and Muslim migrants for HPV, MMR, and influenza vaccines. Social norms, cultural acceptability, and stigma were noted to be barriers to vaccination uptake in several studies. For example, Somali Muslim communities felt HPV vaccination promoted promiscuous sexual behaviour and was unnecessary, as Somali women are expected to not engage in premarital sex. Studies also suggested that migrants' vaccination perceptions (including anti-vaccination sentiment) were influenced by a reliance on information and messages from their home countries, including friends, family, (social) media, and other online resources. Five studies highlighted how a lack of information could lead to exposure to misinformation from unofficial sources, presenting further barriers to uptake. Alienation and disempowerment were themes that arose in some studies. Distrust of the healthcare system and fear of being questioned about one's legal status was reported as a barrier both to accessing, and accepting, routine and COVID-19 vaccination.

There were multiple facilitators relating to acceptance. Holding a positive attitude towards vaccination and its benefits, confidence in the advice of HCPs, positive religious beliefs about vaccination, and normalisation of vaccination were identified as facilitators. Reframing the language and messaging around vaccination helped address cultural barriers; for example, emphasising that HPV vaccination prevents cervical cancer, rather than a sexually transmitted infection, and linking the benefits of vaccination to religious teachings can be helpful. Having access to a trusted information source, often medical, and HCP recommendations were also important.

In terms of awareness of the need for, and availability of, vaccination, knowledge barriers in migrants included low health literacy, with many migrants saying they struggled to find credible and trustworthy information about vaccination in their own language. Two studies found that migrant adolescents had limited knowledge about the existence of common vaccines, including measles and polio, and were unlikely to actively seek out vaccine-related information.

With regard to affordability of vaccination (financial and non-financial), cost was found to be prohibitive when assessed hypothetically, or where self-payment was required. Competing priorities and rigidity of scheduling were non-financial barriers to vaccination, including among parents who were positive about vaccination or intended to vaccinate their children. Where prebooked appointments were poorly attended by Romanian and Romanian Roma migrants, HCPs found that offering walk-in vaccination clinics improved attendance.

The final 5A, activation and nudging towards vaccination, was reflected in studies revealing that face-to-face communication and outreach (e.g., during community visits) were generally effective and well received by Romanian and Roma communities, for example, and helped to increase trust. Initiatives that built trust and shared responsibility through local partnerships and collaboration were also effective. HCPs suggested that involving community members as vaccine advocates could help promote vaccination in communities that had experienced measles outbreaks.

The review identified 23 specific determinants of undervaccination in migrant populations, including that those from Africa, eastern Europe, the eastern Mediterranean, and Asia, as well as recently arrived migrants, refugees, or asylum seekers were most likely to be undervaccinated. One hypothesis is that these findings reflect diminishing trust in authorities and vaccine confidence in eastern Europe and access barriers and interrupted childhood immunisation campaigns in remote and conflict settings. The association with geographical origin more broadly, and recent arrival, could indicate language barriers, which are experienced almost universally by newly arrived migrants. A range of other possible determinants were also identified, suggesting that the reasons for undervaccination of migrants are highly variable and influenced by context. The studies did not identify a strong overall association with gender or age.

Notably, at the policy level, national vaccination strategies and guidelines vary considerably across Europe and many countries do not specifically include refugees and migrants in their vaccination plans (including for COVID-19) or fail to implement them correctly. The researchers argue that "steps should be taken to reduce legal barriers to, and increase opportunities for, migrants to access routine and catch-up vaccination. In the short term, strengthening the capacity of host country health systems to enable more opportunities and novel access points for catch-up vaccination of migrants, particularly older adolescents and adults, is vital...Longer-term measures should focus on improving coordination of policies, guidelines, and vaccination delivery for migrants and mobile populations across European borders."

In addition, "measures must tackle the systemic barriers to accessing vaccination by creating more culturally competent health systems. Migrants described lacking trust in the health system, and struggling to communicate with HCPs and access or understand vaccination information, which led them to avoid care, delay vaccination, or turn to alternative sources, including social media....[F]indings demonstrate that migrants need more linguistically, socially, religiously, and culturally tailored information, in a variety of formats, to make informed decisions about their health, including vaccination, particularly those who might already be reluctant or hesitant to vaccinate....Producing these types of resources should be prioritised by public health bodies."

"Among the limited number of studies reporting facilitators to vaccine uptake, tailored vaccination messaging (based on specific perceptions, beliefs, or barriers), community outreach, and interventions to nudge behaviour (eg, personalised reminders) were shown to be effective....[G]overnments should recognise the importance of clear and transparent communication in any vaccination campaign, and after vaccine development continue to invest funds in developing strong communication and vaccine roll-out strategies to gain and maintain the trust of - and reach - their entire population. Existing research evidence around effective vaccine communication, and new toolkits to combat vaccine misinformation produced during the pandemic, provide useful guidance."

Reflecting on future research directions, the researchers suggest: "Robust research is now needed to study associations at the subregional level and to control for potential confounders, alongside exploring innovative approaches to engaging marginalised migrant populations in vaccination and to ensure equitable access. Future research must also use clear migrant definitions to define subpopulations, study generational effects, and explore how migrants' vaccination views and behaviours might change over time in the host society. Opportunities to conduct subanalyses on migrants in general population studies, where data are disaggregated, should also be explored."

In conclusion, this review has shown that "access to and acceptance of vaccination are key factors influencing vaccine uptake in migrant populations in the EU and EEA, requiring multilevel action. Vaccination services should be designed to better meet patients' social, cultural, and linguistic needs....Tailored and evidence-informed strategies should be codesigned with migrant populations to address specific barriers and perceptions towards vaccines and vaccination in context. Effective and unambiguous communication of public health messages, delivered by trusted messengers, will be vitally important to reach and gain the trust of migrant populations, and to combat the spread of misinformation..."