Defining hard-to-reach populations for vaccination

Extending the benefits of vaccination to everyone who is eligible requires an understanding of which populations current vaccination efforts have struggled to reach. A clear definition of “hard-to-reach” populations – also known as high-risk or marginalized populations, or reaching the last mile – is essential for estimating the size of target groups, sharing lessons learned based on consistent definitions, and allocating resources appropriately. A literature review was conducted to determine what formal definitions of hard-to-reach populations exist and how they are being used, and to propose definitions to consider for future use. Overall, we found that (1) there is a need to distinguish populations that are hard to reach versus hard to vaccinate, and (2) the existing literature poorly defined these populations and clear criteria or thresholds for classifying them were missing. Based on this review, we propose that hard-to-reach populations be defined as those facing supply-side barriers to vaccination due to geography by distance or terrain, transient or nomadic movement, healthcare provider discrimination, lack of healthcare provider recommendations, inadequate vaccination systems, war and conflict, home births or other home-bound mobility limitations, or legal restrictions. Although multiple mechanisms may apply to the same population, supply-side barriers should be distinguished from demand-side barriers. Hard-to-vaccinate populations are defined as those who are reachable but difficult to vaccinate due to distrust, religious beliefs, lack of awareness of vaccine benefits and recommendations, poverty or low socioeconomic status, lack of time to access available vaccination services, or gender-based discrimination. Further work is needed to better define hard-to-reach populations and delineate them from populations that may be hard to vaccinate due to complex refusal reasons, improve measurement of the size and importance of their impact, and examine interventions related to overcoming barriers for each mechanism. This will enable policy makers, governments, donors, and the vaccine community to better plan interventions and allocate necessary resources to remove existing barriers to vaccination.     

Determinants of influenza vaccination timing

New guidelines recommend different influenza vaccination timing for different subpopulations due to the limited availability of flu shots (FS). This study's objectives are to develop a theoretical model to demonstrate why some individuals choose to receive an early FS while others choose a late FS and to empirically explore the determinants of vaccination timing. Empirical results generally supported the theoretical results. Individuals vary their FS timing in response to variations in perceived risks, chronic condition levels reflecting their risk of influenza infection, and opportunity costs, measured by the presence of medical care other than an FS.     

Project VIVA: a multilevel community-based intervention to increase influenza vaccination rates among hard-to-reach populations in New York City

Objectives. We sought to determine whether the work of a community-based participatory research partnership increased interest in influenza vaccination among hard-to-reach individuals in urban settings.Methods. A partnership of researchers and community members carried out interventions for increasing acceptance of influenza vaccination in disadvantaged urban neighborhoods, focusing on hard-to-reach populations (e.g., substance abusers, immigrants, elderly, sex workers, and homeless persons) in East Harlem and the Bronx in New York City. Activities targeted the individual, community organization, and neighborhood levels and included dissemination of information, presentations at meetings, and provision of street-based and door-to-door vaccination during 2 influenza vaccine seasons. Participants were recruited via multiple modalities. Multivariable analyses were performed to compare interest in receiving vaccination pre- and postintervention.Results. There was increased interest in receiving the influenza vaccine postintervention (P<.01). Being a member of a hard-to-reach population (P=.03), having ever received an influenza vaccine (P<.01), and being in a priority group for vaccination (P<.01) were also associated with greater interest in receiving the vaccine.Conclusions. Targeting underserved neighborhoods through a multilevel community-based participatory research intervention significantly increased interest in influenza vaccination, particularly among hard-to-reach populations. Such interventions hold promise for increasing vaccination rates annually and in pandemic situations.National guidelines recommend annual influenza vaccination for high-risk groups—specifically, persons 50 years and older and persons of any age with chronic medical conditions and their household contacts.1 Despite these guidelines and the patent benefits of influenza vaccination—including reductions in influenza-related morbidity and mortality, attendant health care costs, and productivity losses2—vaccination rates among adults in the United States remain lower than recommended levels, especially among elderly with high-risk conditions and racial/ ethnic minorities.1^,3^–5Although data are sparse, influenza vaccination rates are particularly low among marginalized hard-to-reach urban populations such as substance abusers, undocumented immigrants, and homebound elderly.6 During the 2004–2005 influenza vaccine shortage, the vaccination rate was 21% among hard-to-reach populations in designated priority groups for vaccination, compared with estimates of 42% among designated priority groups in the general population during this same period.7 Members of these hard-to-reach groups are less likely to access routine health care or have a health care provider.8^–10 Low vaccination rates combined with risk factors and barriers to accessing health care place hard-to-reach populations at particularly high risk for influenza and attendant morbidity.Additionally, the need for improvements in annual influenza coverage is coupled with recent concern for the potential of a human influenza pandemic.11^,12 Unvaccinated persons within the larger population may propagate disease, particularly in the event of a pandemic.2^,13 Consequently, public health officials face mounting pressure to vaccinate persons in all risk groups and to do so in a brief period of time.14^–16 Members of disadvantaged, urban, multiethnic communities may face additional challenges during a pandemic, including increased vulnerability and transmissibility from overcrowded living conditions, reliance on mass transportation, and limited access to health care.17Although there have been some previous efforts to vaccinate high-risk populations, few were community-based.18 Community-based programs that contributed to increased vaccination coverage have included vaccination at syringe exchange sites,19 an immunization “blitz” in a neighborhood with widespread injection drug use,20 interventions in religion-based neighborhood health centers, and public service announcements and mailings targeted to racial/ethnic minority Medicaid populations.21^,22 Interventions in medical settings have included components such as standing orders,23^,24 mailings,25^–27 education,28^–30 targeted advertising,31 and visiting nurse programs.32 Unfortunately, these efforts may have had little impact on hard-to-reach populations, because members of these groups are less likely to access routine health care.In December 2003, members of the Harlem Community and Academic Partnership,33 comprised of representatives from community and academic organizations committed to implementing interventions by using a community-based participatory research (CBPR) approach, formed an intervention working group to address challenges in vaccinating local hard-to-reach populations. Community-based participatory research is a collaborative process among researchers and community members that emphasizes building trust, equitable power sharing, capacity building, and long-term commitment from all involved in the research process.34^–36 The intervention working group, which was comprised of members representing community residents, community-based organizations (CBOs), academic institutions, and the local health department, met regularly throughout the project to develop the research agenda and study design and to guide project implementation and evaluation. Guided by the Harlem Community and Academic Partnership principles of collaboration, the working group adopted a participatory approach to decisionmaking processes. A multilevel study design was chosen to address individual, social, and contextual factors related to access to, and acceptance of, the influenza vaccine among hard-to-reach populations.37^,38 The working group developed methods to target intervention activities to 3 levels: neighborhood, CBO, and individual.The overall goal of the Project VIVA (Venue-Intensive Vaccines for Adults) intervention was to develop, implement, and assess a rapid-vaccination protocol for hard-to-reach populations that would increase interest in vaccination, provide free vaccination during 2 influenza seasons, and establish a model for the rapid vaccination of individuals that could be generalizable to other urban areas. We report the results of Project VIVA, including pre–post surveys in the 8 target areas within East Harlem and the Bronx, New York City, that evaluated whether interest in receiving influenza vaccination changed after intervention.     

Determinants of influenza vaccination among young Taiwanese children

ObjectiveAccording to the Health Belief Model (HBM), individual perceptions of susceptibility, severity, benefit, barrier, self-efficacy, and cues to action are associated with health actions. In this study, we investigated the perceptions and social factors that influence the intention to vaccinate children against influenza among parents of young Taiwanese children.MethodsA nationwide survey was performed using stratified random sampling to explore the beliefs, attitudes, and intentions of parents/main caregivers with regard to vaccinating children aged 6 months to 3 years against influenza. A questionnaire was developed based on the HBM and multivariate logistic regression analyses of 1300 eligible participants were used to identify significant predictors of the intention to vaccinate.ResultsGreater perceived benefit, cues to action, and self-efficacy of childhood vaccination against influenza were positively associated with the intention to vaccinate. Children's experience of influenza vaccinations in the past year was also a positive predictor. However, perceived susceptibility, perceived severity regarding influenza and perceived barriers to vaccination were not predictive of the intention to vaccinate.ConclusionIn addition to perceived benefits and cues to action, self-efficacy of parents/main caregivers was significantly predictive of their intention to accept influenza vaccination for their young children. These components of the HBM could be used in formulating strategies aimed at promoting the use of influenza vaccine.     

A systems map of the economic considerations for vaccination: Application to hard-to-reach populations

BackgroundUnderstanding the economics of vaccination is essential to developing immunization strategies that can be employed successfully with limited resources, especially when vaccinating populations that are hard-to-reach.MethodsBased on the input from interviews with 24 global experts on immunization economics, we developed a systems map of the mechanisms (i.e., necessary steps or components) involved in vaccination, and associated costs and benefits, focused at the service delivery level. We used this to identify the mechanisms that may be different for hard-to-reach populations.ResultsThe systems map shows different mechanisms that determine whether a person may or may not get vaccinated and the potential health and economic impacts of doing so. The map is divided into two parts: 1) the costs of vaccination, representing each of the mechanisms involved in getting vaccinated (n = 23 vaccination mechanisms), their associated direct vaccination costs (n = 18 vaccination costs), and opportunity costs (n = 5 opportunity costs), 2) the impact of vaccination, representing mechanisms after vaccine delivery (n = 13 impact mechanisms), their associated health effects (n = 10 health effects for beneficiary and others), and economic benefits (n = 13 immediate and secondary economic benefits and costs). Mechanisms that, when interrupted or delayed, can result in populations becoming hard-to-reach include getting vaccines and key stakeholders (e.g., beneficiaries/caregivers, vaccinators) to a vaccination site, as well as vaccine administration at the site.ConclusionDecision-makers can use this systems map to understand where steps in the vaccination process may be interrupted or weak and identify where gaps exist in the understanding of the economics of vaccination. With improved understanding of system-wide effects, this map can help decision-makers inform targeted interventions and policies to increase vaccination coverage in hard-to-reach populations.     

Determinants of vaccination in an urban population in Conakry, Guinea.

A community survey was conducted in 1989 in Conakry, Guinea to determine reasons for low vaccination coverage. Some 377 children aged 12-23 months and their guardians were studied, of whom 204 (54%) had vaccination records. According to their records 19% of children were fully and correctly vaccinated. Thirty-nine incompletely vaccinated children (19% of those with records) had sufficient documented contacts with health services to be fully vaccinated, but at least one immunization opportunity was missed. Multivariate analyses were conducted to identify factors associated with receipt of first dose diphtheria/pertussis/tetanus/oral polio vaccine (DPT/OPV) and with completion of the DPT/OPV series. Factors determining initiation of the series included maternal education (assessed by ability to speak French), household possession of a television, maternal age less than 35 years, child's birth in hospital, and, for non-French speakers, the mother considering vaccination to be affordable. Factors determining completion of the DPT/OPV series, among children who began vaccination, included maternal education, employment, and past positive experience with vaccination services (short waiting times, not having been turned away from vaccination, and not knowing a child with a post-vaccine 'abscess'). Vaccination coverage can be substantially increased in Conakry by improving health services to avoid missed opportunities, following the vaccination schedule correctly, reducing waiting times and avoiding abscesses.     

A venue-based method for sampling hard-to-reach populations

Constructing scientifically sound samples of hard-to-reach populations, also known as hidden populations, is a challenge for many research projects. Traditional sample survey methods, such as random sampling from telephone or mailing lists, can yield low numbers of eligible respondents while non-probability sampling introduces unknown biases. The authors describe a venue-based application of time-space sampling (TSS) that addresses the challenges of accessing hard-to-reach populations. The method entails identifying days and times when the target population gathers at specific venues, constructing a sampling frame of venue, day-time units (VDTs), randomly selecting and visiting VDTs (the primary sampling units), and systematically intercepting and collecting information from consenting members of the target population. This allows researchers to construct a sample with known properties, make statistical inference to the larger population of venue visitors, and theorize about the introduction of biases that may limit generalization of results to the target population. The authors describe their use of TSS in the ongoing Community Intervention Trial for Youth (CITY) project to generate a systematic sample of young men who have sex with men. The project is an ongoing community level HIV prevention intervention trial funded by the Centers for Disease Control and Prevention. The TSS method is reproducible and can be adapted to hard-to-reach populations in other situations, environments, and cultures.     

Determinants of influenza and pneumococcal vaccination in elderly people: a systematic review

OBJECTIVES: Despite strong national and international recommendations on immunization practices, rates for influenza (IV) and pneumococcal vaccinations (PV) are low. We aimed to review international immunization rates and to analyze attitudes and beliefs regarding IV and PV. STUDY DESIGN: Systematic review. METHOD: The MEDLINE database search comprised articles from 1966 to October 2005. Fourteen surveys evaluating a total number of 49292 participants in nine different countries were included into the analysis. RESULTS: Vaccination rates among risk groups do vary significantly between different countries, reaching highest rates in the USA (IV, 82%; PV, 71%) and lowest in former West-Germany for IV (37%) and in Israel for PV (20%). Recommendations by doctors play a central role in promoting IV and PV. The main reason for not being vaccinated was lack of information. CONCLUSION: Specific strategies targeted at groups are needed to increase the knowledge of IV and PV, and thereby decrease incidences of acute lung diseases.     

Systematic review of the costs for vaccinators to reach vaccination sites: Incremental costs of reaching hard-to-reach populations

IntroductionEconomic evidence on how much it may cost for vaccinators to reach populations is important to plan vaccination programs. Moreover, knowing the incremental costs to reach populations that have traditionally been undervaccinated, especially those hard-to-reach who are facing supply-side barriers to vaccination, is essential to expanding immunization coverage to these populations.MethodsWe conducted a systematic review to identify estimates of costs associated with getting vaccinators to all vaccination sites. We searched PubMed and the Immunization Delivery Cost Catalogue (IDCC) in 2019 for the following costs to vaccinators: (1) training costs; (2) labor costs, per diems, and incentives; (3) identification of vaccine beneficiary location; and (4) travel costs. We assessed if any of these costs were specific to populations that are hard-to-reach for vaccination, based on a framework for examining supply-side barriers to vaccination.ResultsWe found 19 studies describing average vaccinator training costs at $0.67/person vaccinated or targeted (SD $0.94) and $0.10/dose delivered (SD $0.07). The average cost for vaccinator labor and incentive costs across 29 studies was $2.15/dose (SD $2.08). We identified 13 studies describing intervention costs for a vaccinator to know the location of a beneficiary, with an average cost of $19.69/person (SD $26.65), and six studies describing vaccinator travel costs, with an average cost of $0.07/dose (SD $0.03). Only eight of these studies described hard-to-reach populations for vaccination; two studies examined incremental costs per dose to reach hard-to-reach populations, which were 1.3–2 times higher than the regular costs. The incremental cost to train vaccinators was $0.02/dose, and incremental labor costs for targeting hard-to-reach populations were $0.16–$1.17/dose.ConclusionAdditional comparative costing studies are needed to understand the potential differential costs for vaccinators reaching the vaccination sites that serve hard-to-reach populations. This will help immunization program planners and decision-makers better allocate resources to extend vaccination programs.     

Predictors of influenza vaccination in an urban community during a national shortage

Little is known about the impact of vaccine shortages on vaccination rates among disadvantaged populations in the United States. We compared factors associated with influenza vaccination rates during a vaccine shortage (2004-2005) and a non-shortage (2003-2004) year among adults in predominantly minority New York City neighborhoods. Thirty-one percent of participants received influenza vaccine during the non-shortage year compared with 18% during the shortage. While fewer people received the influenza vaccine during the shortage, a higher proportion of the vaccinated were in a high-risk group (68% vs. 52%, respectively). People were less likely to have been vaccinated during the shortage if they were Black. This study suggests that vaccination rates were lower during the shortage period among Blacks and those who are not explicitly a focus of national vaccination outreach campaigns. Such groups are less likely to be vaccinated when vaccines are scarce.     

Use of mobile phones for improving vaccination coverage among children living in rural hard-to-reach areas and urban streets of Bangladesh

In Bangladesh, full vaccination rates among children living in rural hard-to-reach areas and urban streets are low. We conducted a quasi-experimental pre-post study of a 12-month mobile phone intervention to improve vaccination among 0–11 months old children in rural hard-to-reach and urban street dweller areas. Software named “mTika” was employed within the existing public health system to electronically register each child's birth and remind mothers about upcoming vaccination dates with text messages. Android smart phones with mTika were provided to all health assistants/vaccinators and supervisors in intervention areas, while mothers used plain cell phones already owned by themselves or their families. Pre and post-intervention vaccination coverage was surveyed in intervention and control areas. Among children over 298 days old, full vaccination coverage actually decreased in control areas – rural baseline 65.9% to endline 55.2% and urban baseline 44.5% to endline 33.9% – while increasing in intervention areas from rural baseline 58.9% to endline 76*8%, difference +18.8% (95% CI 5.7–31.9) and urban baseline 40.7% to endline 57.1%, difference +16.5% (95% CI 3.9–29.0). Difference-in-difference (DID) estimates were +29.5% for rural intervention versus control areas and +27.1% for urban areas for full vaccination in children over 298 days old, and logistic regression adjusting for maternal education, mobile phone ownership, and sex of child showed intervention effect odds ratio (OR) of 3.8 (95% CI 1.5–9.2) in rural areas and 3.0 (95% CI 1.4–6.4) in urban areas. Among all age groups, intervention effects on age-appropriate vaccination coverage were positive: DIDs +13.1–30.5% and ORs 2.5–4.6 (p < 0.001 in all comparisons). Qualitative data showed the intervention was well-accepted. Our study demonstrated that a mobile phone intervention can improve vaccination coverage in rural hard-to-reach and urban street dweller communities in Bangladesh. This small-scale successful demonstration should serve as an example to other low-income countries with high mobile phone usage.     

Determinants of parents' reticence toward vaccination in urban areas in Benin (West Africa)

Background

Despite the efforts of health authorities, vaccination coverage of targeted child populations is still poor in many regions. Parents' reticence has been identified as one cause of this situation. However, there is little data to explain the phenomenon that could support decision-making.

Objective

The objective of the study was to uncover the determinants of this reticence toward vaccination among the religious population of the cities of Parakou and Cotonou in Benin.

Methods

This was an exploratory study using a qualitative survey of 12 pastors and 30 faithful from churches that are vaccination-reticent and a control group of the same number of faithful belonging to other churches, all Christian. Individual and group interviews were carried out in the local language using a pre-established and pre-tested guide. The data collected underwent discourse content analysis focused on specific themes.

Results

Analysis of the data reveals an erroneous perception of child vaccination. Those who are reticent say vaccination goes against the will of God, that it is a poison from the "white witch doctor", and that those who vaccinate their children are committing a sin. Members of the control group argued against this, but without conviction. They adhere to the principle of obedience to authority, a biblical precept invoked when the vaccinators oblige them to vaccinate their children. Other factors were identified that could explain the reticence, such as the tactlessness of the vaccinators, parents' previous experiences and false rumours about vaccination.

Conclusion

The reasons for reticence are mainly related to parents' beliefs in religious principles that are sometimes poorly understood. To limit the spread of this phenomenon, more detailed information and negotiation between the health authorities and the pastors of these churches are essential.

Abstract in French

See the full article online for a translation of this abstract in French.

     

Community-academic research on hard-to-reach populations: benefits and challenges

In this article, the authors examine some of the benefits and challenges associated with conducting research on hard-to-reach/hidden populations: in this instance, sex workers. The population studied was female and male sex workers working in different sectors of the sex industry in a medium-size Canadian metropolitan area. The authors describe the need for close community-academic cooperation, given the hidden and highly stigmatized nature of the target population that was investigated and the local context in which the research project was embedded. The authors discuss the main benefits and challenges of the research collaboration for the various parties involved, including the community partner organization, indigenous research assistants, and academic research team. They conclude with a discussion of strategies to help overcome the main challenges faced during the research endeavor.     

Rural,urban, and suburban differences in influenza vaccination coverage among children

Influenza vaccination is the primary way to prevent influenza, yet influenza vaccination coverage remains low in the United States. Previous studies have shown that children residing in rural areas have less access to healthcare and lower vaccination coverage for some vaccines. Influenza vaccination coverage among children 6 months–17 years by rural/urban residence during the 2011–12 through 2018–19 influenza seasons was examined using National Immunization Survey-Flu data. The Council of American Survey Research Organizations response rates for National Immunization Survey-Flu ranged from 48% to 65% (2011–12 through the 2017–18 seasons) for the landline sample and 20%–39% (2011–12 through the 2018–19 seasons) for the cellular telephone sample. Children residing in rural areas had influenza vaccination coverage that ranged from 7.9 (2012–13 season) to 12.6 (2016–17 season) percentage points lower than children residing in urban areas, and ranged from 4.5 (2012–13 season) to 7.4 (2016–17 season) percentage points lower than children residing in suburban areas. The differences in influenza vaccination coverage among rural, suburban, and urban children were consistent over the eight seasons studied. Lower influenza vaccination coverage was observed among rural children regardless of child’s age, mother’s education, household income, or number of children under 18 years of age in the household. Rural versus urban and suburban differences in influenza vaccination coverage remained statistically significant while adjusting for selected sociodemographic characteristics. A better understanding of the reasons for lower childhood influenza vaccination coverage for children in rural and suburban areas is needed.     

Use of mark-recapture techniques to estimate the size of hard-to-reach populations

OBJECTIVES: To review the main problems associated with mark-recapture methods of population estimation, and to indicate some practical strategies for addressing these problems, with illustrations from a study of drug-use prevalence across Wales. METHODS: Unnamed identifier data were collected in 1994 on 2610 drug users who were in contact with various agencies across Wales: the police, drug treatment agencies, needle exchanges, probation services, and agencies reporting to the Welsh Drugs Misuse Database. RESULTS: Based on the dependency relationships between different agencies' datasets, different estimates of the 'hidden' populations (not in contact with agencies) were modelled for each county, for males and females, for injecting drug users and serious drug users, and for those under 25 and those over 25 years of age. Different models were also constructed for the same subpopulations, using different agency datasets and different criteria of overlap between them, yielding a total of 230 different models. CONCLUSIONS: The issues of sample heterogeneity and population definition are particularly intractable in mark-recapture studies. Sample heterogeneity may be partly addressed by separately modelling different subpopulations to check whether they show the same dependency relationships as the main population. Population definition may be partly addressed by restricting modelling to datasets thought to share roughly congruent population definitions.     

Harnessing expertise: involving peer interviewers in qualitative research with hard-to-reach populations

The use of peer interviewers with privileged access to a particular population group, which is difficult to reach via more conventional methods, has been acknowledged in recent research. This paper explores a number of key issues relating to the employment of peer interviewers by reflecting on a project designed to explore the views and experiences of parents who use illegal drugs. The project presented the research team with a number of challenges. These included the need to provide on-going support for the interviewers, a sense of distance felt by the researchers from the raw data they collected, and the difficulties of gaining from the skills and experiences of peer interviewers without exploiting their labour. The paper also explores the advantages of involving peer interviewers closely in research work and reflects on the nature and boundaries of expert knowledge that can become evident in such collaborations. The need for a certain amount of flexibility over the roles and domains of control that lay experts and researchers traditionally inhabit is suggested. In conclusion, it is argued that the involvement of peer interviewers in research can be a valuable means of enhancing our knowledge and understanding of a variety of population groups who tend to live beyond the gaze of more orthodox researchers.