Social determinants of health and seasonal influenza vaccination in adults ≥65 years: a systematic review of qualitative and quantitative data

The global burden of inter-pandemic influenza is estimated at 1 billion cases of flu, 3–5 million cases of severe illness, and 300,000-500,000 deaths annually [1], with about 90% of all influenza-related deaths occurring in adults aged 65 years or more and well-defined risk groups [2, 3]. Influenza is an important contributor to the annual increase in hospitalizations and deaths attributed to pneumonia and influenza that is observed during the winter months, particularly among those ≥65 years old or those with chronic medical conditions including pulmonary, cardiovascular, or renal diseases as well as immunosuppression [3]. The primary goal of influenza vaccination in these high risk groups is to prevent unnecessary hospitalizations and premature deaths related to influenza, since episodes of influenza tend to exacerbate chronic medical conditions and lead to the occurrence of secondary bacterial pneumonias.

In the general population, immunization against influenza is considered the most important public health intervention to control seasonal, epidemic, and pandemic influenza [3‐5]. Priority approaches and strategies to respond to an influenza pandemic are to achieve appropriate rates of vaccine uptake [6]. This would increase seasonal vaccine demand to stimulate market forces and augment supply, thus expanding the production capacity in a sustainable way [4, 5]. There are, however, marked differences among countries’ capacities, priorities, and resources to establish influenza vaccination policies and strategies [7‐10].

There have been previous reports, reviews [11], and a recent Cochrane systematic review [12] to assess the effectiveness of vaccines in preventing influenza, influenza-like illness, hospital admissions, and mortality in the elderly. For community dwelling elderly, the adjusted analyses from cohort and case control studies in the Cochrane review show that the effectiveness of the vaccine is modest, with reductions in the risk of hospitalizations for influenza or pneumonia, for respiratory or cardiac diseases, and for all-cause mortality (cohort studies) or death specifically from influenza and pneumonia (case–control studies) [12].

Other studies have tried to identify determinants of seasonal influenza vaccination [13], but few have focused on identifying social determinants within a framework of health equity [14] or their focus has been in other age groups [15]. Social determinants of health (SDH) play a critical role in disease occurrence, distribution, and consequences.

A Cochrane review about interventions to increase influenza vaccination rates of the elderly in the community found (with evidence from randomized controlled trials in developed countries) that personalized postcards and phone calls are effective, home visits and facilitators may be effective, but reminders to physicians are not [16]. This review did not include randomized controlled trials of society-level interventions or qualitative studies. To improve the understanding of the multidimensional challenge of yearly seasonal influenza vaccination among the elderly, the aim of this review was to assess the barriers that prevent elderly people from accessing and accepting seasonal influenza vaccine and its related social determinants. We used the conceptual framework that the Commission on Social Determinants of Health (CSDH) developed to identify determinants linked to seasonal influenza vaccination. This framework is based on a social production of disease approach, in which individual health outcomes and diseases and their unequal distribution across population groups are the result of the interaction of several determinants operating at different domains [17, 18] (Figure 1). This framework contains three types of determinants: 1) Structural determinants; 2) Intermediate determinants; and 3) Determinants associated with the healthcare system.

In this systematic review we considered qualitative and quantitative studies on seasonal influenza vaccination and related interventions among elderly adults (age≥65) living in the community or in nursing homes in high, middle, and low income countries (Table 1). The outcome measure of interest was vaccine coverage and the exposures of interest were barriers that patients and health services faced to obtain and deliver seasonal influenza vaccine as well as the social health determinants linked to those barriers. Since the aim of our study was not the effectiveness of the vaccine, but the barriers (and their related social determinants) that may affect vaccine uptake, we searched qualitative and descriptive studies that answered questions about structural determinants (e.g. individual socio-economic conditions, public policies, cultural norms) as well as intermediate determinants of health (e.g. attitudes, beliefs, lifestyles) [17, 18].

Overall, 80 studies were identified as suitable for this review. Given the limited number of studies retrieved about nursing homes (5), homebound patients (2), and interventions (15, from 3 countries) we decided to leave those topics for future studies. From the 58 studies included, 13 used qualitative methods, 3 used mixed qualitative and quantitative approaches and 42 used quantitative or descriptive methods (Appendix 2). There were 13 studies about policy and strategy problems, six about healthcare providers, and 39 regarding patients’ beliefs, attitudes, socio-economic factors, or material circumstances. Nine studies were multinational, including countries from Asia, Europe, Latin America, and the Middle-East. More than half of the studies were done in developed countries. Only six studies included patients from rural areas [27‐35]. Qualitative data collection techniques included one-on-one interviewing, questionnaires, key informant selection, focus groups, participant observation, participatory action research, and community mobilization techniques. Quantitative studies encompassed mainly descriptive studies and cross sectional surveys, two ecologic studies, and one controlled trial [36].

Themes about SDH emerged from each component of the immunization process (policy and governance, healthcare systems, provider, and patient) and were organized according to the categories in the conceptual framework of the SDH (Figure 1): structural, intermediate, and health system determinants (Table 2). In addition, barriers and determinants of patient’s beliefs and behaviors on influenza vaccination are described in Figure 3, while reasons for vaccine acceptance or refusal among elderly adults are summarized in Table 3.

The effectiveness of influenza immunization for both seasonal and pandemic influenza depends upon a timely and sufficient supply of the vaccine. Even if all social barriers to implement or strengthen seasonal influenza immunization in the elderly are removed, equitable access to SIV remains an issue for many low- or middle-income countries. There is an increasing push by the World Health Organization to eliminate disparities in seasonal immunization rates among and within Member States as part of resolution World Health Assembly (WHA) 56.19, which in 2003 recommended the adoption and/or strengthening of influenza vaccination policies to increase seasonal influenza vaccination coverage among populations at high risk of complications and death [5]. The WHO Global Influenza Vaccine Action Plan has improved the availability of seasonal influenza vaccine for a significant number of middle and low-income countries [37, 38]. As a result, influenza vaccination is increasing throughout the world, especially in middle-income countries of Latin America and Central and Eastern Europe. Of note, countries that provide reimbursement for healthcare practitioners to administer influenza vaccine or provide seasonal influenza vaccine within their public health insurance coverage tend to have higher seasonal influenza vaccination for the elderly [39, 41]. However, no country has fully implemented its own vaccine recommendations and substantial variations in influenza vaccination persist among countries in most regions of the world [37, 39, 40]. Even in wealthy industrialized countries, significant population groups at risk of complications from influenza remain unvaccinated or refuse the vaccine. In this systematic review, we identified the importance of social determinants of health in regards to seasonal influenza immunization. This is relevant given the current efforts to expand seasonal influenza vaccination into low and middle income countries. Decision makers, when designing public health interventions, can consider the full range of determinants that influence the effective coverage of programs. As many of these determinants operate outside the health sector, decision makers will also need to consider the adoption of mechanisms for intersectoral action.

Socio-cultural aspects and social support may affect vaccine acceptance. At an individual level, factors such as physicians’ advice, cost, convenience, perceived susceptibility, prior experiences, health status, personal beliefs, and misconceptions about the vaccine and the disease mainly shaped the vaccine acceptance among this population [30, 47, 48, 51].

In contrast to other routine immunizations, the effectiveness of seasonal influenza vaccine requires yearly administration to high-risk groups that develop complications or death associated with influenza infection. Due to the constant risk of antigenic drift, there is a need for yearly selection of circulating viral strains, and the effectiveness is directly related to the degree of match between vaccine virus and circulating strains. This feature adds other important financial and programmatic barriers to the expansion of seasonal immunization agendas that has burdened some national immunization programs in prioritizing financial and human resources.

Once the historical, financial, political, and epidemiological dimensions of implementing a seasonal influenza immunization program are achieved [39], there are operational dimensions of seasonal influenza vaccine programs to consider. As important as availability of a yearly seasonal influenza vaccine is the design and implementation of a variety of strategies and activities to achieve adequate levels of effective immunization coverage among high-risk populations. Even in high-income countries with established SIV programs targeting high-risk populations and available vaccine, the rates of vaccination are far from ideal, while elderly adults at risk of influenza remain reluctant of vaccination [77]. Currently, there is little agreement on the ideal vaccination strategies and the ideal selection of target groups to receive seasonal influenza vaccine [40, 78]. For instance, there is even lack of consensus on the benefit of seasonal influenza vaccination in the elderly [40]. Recent Cochrane Reviews [12] have cast doubt on the scientific evidence behind current consensus recommendations to vaccinate the elderly against seasonal influenza. Moreover, in some regions, a lack of harmonization of vaccination strategies and selection of high-risk populations have contributed to insufficient vaccination coverage of some target groups [42].

Differences in vaccination strategies have provided varied results. In Japan, vaccination against influenza among school-aged children demonstrated an important impact in the elderly [79], while other studies have shown that nationwide vaccination programs may be better alternatives to decrease influenza-associated mortality in the elderly [46]. On the other hand, non-specific preventive measures such as hand-washing, distance, and wearing a mask during periods of risk are useful [40] and even desirable given the difficulty to distinguish influenza from influenza-like illness and the concurrent circulation of diverse respiratory viruses. These supplemental and basic measures should be emphasized in prevention messages, especially when and where there are no means to avoid the barriers against influenza vaccine uptake.

The significance of qualitative research has been increasingly recognized in health sciences disciplines; however, efforts to integrate or synthesize qualitative findings have been relatively limited, particularly with the topic of influenza vaccination [23, 24]. Evidence from qualitative and quantitative studies that examine social determinants of health, factors that shape the delivery and implementation of interventions, and the experience of persons involved in providing and receiving interventions improves the scope and relevance of systematic reviews to policy-makers and practitioners [20, 80, 81]. Furthermore, situating the results of the review within the social determinants of health model may provide a conceptual framework particularly useful for global policy making [18, 82].

This study has certain limitations. The study may have source bias, since we did not search in the grey literature or unpublished studies and used qualitative research and filter terms instead of free text searching [24]. We did not search specific regional databases that may be more suitable to report research from developing countries. As only studies written in English were included, we may have missed studies from developing countries published in other languages. Since more than half of the studies were conducted in developed countries and in urban areas, low and middle-income as well as rural regions may be underrepresented. The inclusion of studies relying on cross-sectional survey methods may introduce selection bias as it is not possible to control for individuals refusing to be interviewed. Most importantly, associations between vaccine uptake and other variables found in cross-sectional surveys do not involve causal relationships [32], and such associations may be confounded by other factors [40, 78, 83]. Limitations of the meta-synthesis methodology similarly include the inability to infer causal relationships from mixed qualitative and quantitative data. There is little consensus on the use of quality appraisal in qualitative meta-synthesis [20]; therefore, we did not exclude any qualitative studies based on quality rating schemes. However, our search strategy was appropriate to explore social determinants in our population of interest.

The fact that most studies evaluated in this systematic review came from high-income countries illustrates that seasonal influenza vaccine is not routinely offered in low and middle-income countries. Particularly, we can assume that non-served and underserved populations are not routinely offered seasonal influenza vaccine because this is not a standard public health practice or a public health priority in many low-and medium income countries, where determinants such as vaccine availability as well as financial and political barriers prevent the effective deployment of these interventions. Finally, because influenza vaccine effectiveness may be suboptimal, especially in older people [12], the opportunity to prevent influenza related complications in this population will benefit from the development of more immunogenic vaccines that could be used and shared at affordable costs to populations in high-, middle-, and low income countries. Newer influenza vaccines such as the universal influenza vaccines may potentially change the landscape of influenza vaccine protection by providing long term protection and avoiding the need of yearly revaccination [5].

Seasonal influenza remains a public health challenge with important economic and social tolls. While the precise epidemiology has not been completely deciphered in middle-and low-income countries, it is likely that this burden is shared globally. Our results also highlight that policies, practices, and vaccination strategies against seasonal influenza vaccination are influenced by social determinants where vaccine is routinely available. Some of these determinants are health-system related, provider-related, or patient-related resulting in variable coverage levels within countries. While vaccination efforts continue to expand to middle-and low income countries, there is minimal representation of underserved populations in currently available reports. This issue demonstrates that larger social determinants influence the availability and vaccination practices in these areas. Incorporating a framework that takes into account social determinants of health into vaccine policy design and implementation may foster immunization equity among the most vulnerable populations against seasonal influenza and likely other vaccine preventable diseases. Incorporating a social determinants framework will also allow decision makers to identify where determinants are located (within or outside the health sector) and serve to adopt mechanisms for intersectoral action to address those determinants originating outside the realm of the health sector.

Keywords used for search

#1 Seasonal influenza vaccine: “Influenza Vaccines”[MeSH] OR “Influenza, Human/prevention and control”[MeSH], “seasonal influenza vaccine” , “seasonal influenza vaccines”, NOT pandemic, NOT epidemic.

#2 Elderly adults: (old* or pension* or retire* or aged or elderly or senior* or geriatric*) or (“long-term care” or “nursing care” or “palliative care” or “homes for the aged” or “nursing homes”), or (Community dwelling, homebound, community ).

#3 Qualitative research: (Qualitative Research[MeSH]) OR (Nursing Methodology Research[MeSH]) OR qualitative or ethnograph* or phenomenol* or ethnonurs* or grounded theory* or (lived experience*) or narrative* or (life experiences) or (cluster sample) or (action research) or (observational method) or (content analysis) or (thematic analysis) or (constant comparative method) (discourse analysis) or (focus group*) or (ethnological research) or ethnomethodolog* or (mixed methods).

#4 SDH, inequalities: “Healthcare Disparities”[Mesh] OR “healthcare disparities” OR “health care disparities” OR “Healthcare Disparity” OR “Health care Disparity” OR “Health Status Disparities”[Mesh] OR “health status disparities” or “health status disparity” OR “Social Class” [Mesh] OR “social mobilities” OR “ social mobility” OR “Poverty Areas”[Mesh] OR “poverty areas” OR “poverty area” OR “slums” OR “slum” OR “ghetto” OR “ghettos” OR “Educational Status”[Mesh] OR “educational status” OR “Educational Achievement*” OR “Illiteracy” OR “Literacy” OR “Cross-Cultural Comparison”[Mesh] OR “Cross-Cultural Comparison” OR “Cross-Cultural Comparisons” OR “Transcultural Studies” OR “Transcultural Study” OR “Prejudice” [Mesh] OR “Prejudice” OR “Prejudices” OR “Racism” OR “Social Discrimination” OR “Sexism” OR “Gender Bias” OR “Sex Bias” OR “Sex Discrimination” OR “Ageism” OR “Segregation” OR “caste” OR “castes” OR “ resource poor” OR “inequities” OR “inequality” OR “inequalities” OR “Socioeconomic Factors”[Mesh] OR “Socioeconomic Status” [Mesh] OR “social class” OR “social classes” OR “socioeconomic status” OR “Social Environment”[Mesh] OR “social environment” OR “social environments” OR “Social Conditions”[Mesh] OR “social conditions” OR “social condition” OR “low income populations” OR “low income population” OR “Vulnerable populations” [Mesh] OR “vulnerable populations” OR “vulnerable population” OR “Sensitive Populations “ OR “Sensitive Population” OR “Disadvantaged” [TI] OR “Social Determinants”[TIAB] OR “socio-economic status” OR “Policy” OR “Government”, OR “social health determinants”, OR “low income”, OR “minority”, poverty,

#5 Barriers:

Barriers, barrier, access barriers, travel time, geographic location, availability of services, geographic distribution of services, provider location, acceptability barriers, acceptance barrier, health behavior, knowledge, belief, beliefs, health belief, attitude, attitudes, mistrust, fear, adequate funding, user fees, out of pocket payment, co-payment, subsidy, referral, service referral, diagnostic kits, surveillance, vaccine stocks, sustainable stocking, immunization barriers.

#6 Interventions:

Advertising, campaign, provider mailings, standing orders, registry-based telephone calls, telephone calls, remainder systems, patient education, staff education, visiting nurses, outreach, visiting physician, patient satisfaction, multi- level, multi-level intervention, single intervention, intervention, interventions, immunization program, program, multidisciplinary, preventive health services, community participation.

Search strategy

#1 Seasonal influenza

#2 Elderly

#3 Qualitative

#4 SDH

#5 Barriers

#6 Interventions

#7 #1 AND #2 Elderly SIV

#8 #4 OR #5 SDH and barriers

#9 #7 AND #8 Elderly, SIV, SDH, Barriers

#10 #3 OR #6 Qualitative research or potential interventions

#11 #9 AND #10 SIV, elderly, barriers, SDH, interventions

Studies for Data Abstraction

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