Factors Related to,and Effective Interventions for,Vaccination Uptake Among Older Adults in Two Asia-Pacific Countries: A Rapid Review

Abstract

This rapid review aimed to present a comprehensive overview of barriers, facilitators, and effective interventions that promote vaccination uptake by older adults in the Asia-Pacific region. Rapid review methodology was applied, using two databases (PubMed, Embase). Articles were included if studies were conducted in Australia, Singapore, Indonesia, and the Philippines; included human population ≥50 years of age, and was published from 2016 to August 2022. Related articles were not found from Indonesia and Philippines. A total of 23 articles met the inclusion criteria, with 19 reporting on barriers and facilitators, whereas, four articles reported effective interventions to promote vaccination uptake. Among the 19 studies that identified barriers and facilitators to vaccination uptake, the more common factors were social influences (n = 8/19), perceived benefits of vaccine (n = 7/19), and perceived vaccine safety (n = 6/19). Interventions that focused on supporting clinicians were found to be effective in leading them to recommend vaccinations among older adults, such as creating awareness on the low baseline vaccination rates among older adults, provision of structured health assessment, and nurse reminders. More studies are needed to ascertain the barriers and facilitators to uptake, as well as to identify effective interventions influencing vaccine uptake among older adults in the Asia-Pacific region.

Keywords

vaccine uptake vaccination immunization adults older people elderly Asia-Pacific barriers facilitators factors interventions

What We Already Know

The number of older adults (aged 65 years or older) is increasing in the Asia-Pacific region.

However, vaccination uptake in this population segment remains low.

Among the common factors influencing vaccination uptake among older adults are those related to health care systems, policy and operational factor, health care provider, and patient and caregiver factors.

What This Article Adds

This rapid review provides an overview of the factors influencing vaccination uptake among older adults in Singapore and Australia.

This review also provides information on effective interventions at promoting vaccination uptake by older adults.

The review also identifies an evidence gap, pointing to a lack of literature on barriers and facilitators to vaccine uptake among older adults in the Philippines and Indonesia.

The findings of this review will help to identify missed opportunities and promote vaccination uptake among older adults, as part of building strengthened and sustainable health systems in Asia-Pacific communities.

Introduction

Saving millions of lives globally each year, vaccination is now considered fundamental to primary health care and public health. The World Health Organization (WHO)¹ has adopted a life-course approach to immunization and healthy aging in the WHO Immunization Agenda 2030 and the UN Decade of Healthy Ageing program. Life-course vaccination is particularly important in Asia-Pacific region as its population ages at an unprecedented pace. In 2020, 24.6% of the population in Asia-Pacific region were aged 50 years or older, with 9.1% aged 65 years or older. This is anticipated to rise to 29.2% and 12.2%, respectively, in 2030, with a sharper increase among the older age group.² Indeed, the number of adults aged 65 years or older in the region is estimated to increase more than twofold, from 535 million in 2015 to about 1.3 billion in 2050.³ Despite the widespread benefits of vaccines, vaccination uptake in this population segment remains low across Asia-Pacific region.⁴ For instance, only 37.3% individuals who are in high-risk group that included older adults reported to taking the influenza vaccination. This is far below the WHO target of 75% for older adults.⁴

To improve vaccination uptake among older adults in Asia-Pacific region, it is essential to understand the related factors and the interventions that have been shown to be effective, specific to this context. Several reviews have reported on factors influencing vaccination uptake among older adults. Among the factors were storage of vaccines, funding and costs (health care systems factor); accessibility and vaccination settings (policy and operational factor); knowledge of vaccines and mechanisms of action, failure to assume the responsibility for vaccination, incomplete or inaccessible documentation of previous vaccinations (health care provider [HCP] factor); and perception that vaccine is ineffective or harmful, and mistrust in health care system (patient and caregiver factor).^5
-7 Some of the reviews covered diverse geographical areas^5,6 or concentrated on a single country,⁷ with none looking specifically at the Asia-Pacific region.

Various interventions for promoting vaccination uptake have been reported in the literature. Interventions aimed at addressing barriers to vaccination uptake among adults aged 60 years or older, such as patient lack of knowledge about vaccination, poor access to vaccines, lack of recommendation from HCPs, and financial considerations, highlighted that interventions, such as pharmacist-driven intervention,^8,9 outreach program,¹⁰ provider education,¹¹ reminder,¹² and providing free vaccination¹³ can improve vaccination uptake. In a recent review by Eiden et al,¹⁴ provider-led educational initiatives and provider recommendations were shown to be more effective than less interactive interventions, such as posters and reminder-recall letters. Interventions targeting HCPs, including awareness campaigns, incentives, affordability efforts, and vaccination site expansion also showed positive associations. However, although studies on interventions for promoting vaccination uptake among older adults covered diverse geographical areas, such focus in the Asia-Pacific setting is still lacking.

This rapid review aims to provide an overview of the known factors related to, and effective interventions, promoting vaccination uptake by older adults in the Asia-Pacific region. More specifically, this review focused on four countries, namely, Australia, Singapore, Indonesia, and the Philippines. These four countries were selected because they represent the diverse nations across the Asia-Pacific region in terms of socioeconomic development, health care structures and policies, and culture. Australia and Singapore have rapidly aging societies, with older adults (aged 65 years or older) constituting 17% and 14% of the population, respectively.¹⁵ Although Indonesia and Philippines have 7% or less of their population aged 65 years or older at present,¹⁶ these countries are also expected to become aging societies by 2030.¹⁷ The findings of this review will help to identify missed opportunities and promote vaccination uptake among older adults, as part of building strengthened and sustainable health systems in Asia-Pacific communities.

Methods

Search Strategy

A literature search was conducted in August 2022, searching PubMed and Embase electronically. The following concepts were used in the literature search: “older people,” “vaccination,” “barriers,” “facilitators,” “intervention,” “strategy,” “Australia,” “Singapore,” “Indonesia,” “Philippines,” and their synonyms or alternative spelling. Keywords of barriers and facilitators pertaining to vaccination among older adults that had been identified in the literature, such as “knowledge,” “internet access,” “information,” “funding,” “cost,” “financial,” “infrastructure,” “policy,” “politics,” “affordability,” and “coverage” were also included in the search strategy for comprehensiveness. Both keywords and MeSH terms were used. The search strategy can be found in Supplemental Table 1, available online.

Selection Criteria

All titles retrieved were imported into the bibliographic management software, EndNote X21. Duplicates were removed. The screening process was guided by recommendations for conducting rapid review by the Cochrane Rapid Reviews Methods Group.¹⁸ Article screening involved two of the authors (AS and AL) screening 20% of all the titles/abstracts, with conflict resolution. AS then screened the remaining titles/abstracts. Excluded titles/abstracts were screened by another author (WTT). This is followed by four authors working in pairs (AS and WTT; MPEN and SCT) to assess the full text of resultant articles (n = 104; 52 for each pair), with the articles divided up equally between pairs (an author in the pair was assigned either 20 or 21 articles). Each author independently assessed the articles assigned to their pair and cross-checked their partner’s excluded articles. Discrepancies were resolved through discussions. Articles assessed were included in or excluded from the review according to the inclusion and exclusion criteria outlined in Figure 1.

The target study populations aged ≥50 years was used because older adults, particularly those aged 50 years and older, are at a higher risk of severe outcomes for diseases, such as COVID-19, influenza, pneumococcal, and shingles. Consequently, national vaccination programs target the age group for recommended vaccines and, in some cases, provide free vaccines to eligible subgroups. In Australia, for instance, pneumococcal vaccine is free for Aboriginal and Torres Strait Islander adult populations aged 50 years and older.¹⁹ In Singapore, adults aged older than 50 years were prioritized in the COVID-19 vaccine campaign.²⁰

During the literature search process, it was found that there were no articles on Indonesia or Philippines. To ensure that articles on these two countries were not missed, the search was run again, but with the publication time frame backtracked to the year 2012 for the two countries. However, the same result was found. Subsequently, emails seeking literature recommendations were sent to vaccination experts who were known to the authors in these two countries, but none were proposed.

Data Extraction

Data extraction was divided into two parts, based on the aims of this review. The first part focused on factors related to vaccination uptake among older adults. The second part focused on effectiveness of interventions for promoting vaccination uptake among older adults. Correspondingly, two sets of data extraction forms were created.

Similar to the process of full-text assessment of articles for inclusion, data extraction was conducted by four authors working in pairs (AS and MPEN; AL and WTT), with the articles divided up between pairs (n = 23; 11 or 12 articles for one of the pairs). Each author independently extracted the articles assigned to their pair (an author in the pair was assigned either five or six articles). Data on the following were extracted from the included articles: author name, publication year, study country, vaccine type, study setting, study design, study population, data analysis methods, factors related to vaccination uptake (where applicable), intervention description and effectiveness for promoting vaccination uptake (where applicable). Once an author finished their share of the data extraction work, their partner cross-checked for correctness and completeness of the extracted data.

Risk of Bias Assessment

The Mixed Methods Appraisal Tool²¹ was used to appraise the quality of included articles. The quality appraisal was again conducted by four authors working in pairs (AS and WT; MPEN and SCT). Each author cross-checked the appraisal done by their partner, and disagreements were resolved through discussions.

Data Analysis and Reporting

Regarding factors related to vaccination uptake among older adults, the data analysis process involved author WTT classifying emerging barriers and facilitators into broader themes. The themes were constructed using a data-driven approach. Using the inductive approach, barriers and facilitators reported in both quantitative and qualitative studies were extracted. Similar factors were then grouped together and categorized into broader themes.

In this review, quantitative, qualitative, and mixed-methods studies were included. For studies that quantified the association between factors and vaccination uptake, odds ratios and P values were extracted when the data were available. For studies that only presented frequencies of factors, the top three most frequent factors reported were included.²² For qualitative studies, unique factors that were not identified in quantitative studies were also included. Whether a factor was deemed negative (barrier) or positive (facilitator) depended on how the descriptions were phrased in the qualitative article. For example, the following was extracted as a negative factor for (barrier to) vaccination:

Seven refusers and defaulters cited being not vulnerable to influenza as a reason for not having the vaccine. Most felt they were not vulnerable because they seldom got influenza. This was reinforced by previous encounters with mild episodes of influenza.²³

Where factors similar to those identified in quantitative studies were found, they were used to confirm or add a perspective to the findings from quantitative studies.

Regarding effectiveness of interventions for promoting vaccination uptake among older adults, interventions identified were classified according to the nine categories defined by the Expert Recommendations for Implementing Change (ERIC) project.²⁴ The effectiveness of the interventions reported was based on the effect of the interventions in influencing the uptake of the specific vaccination in the studies. Where available, P values and odds ratios were reported.

Results

Literature Selection

A total of 1424 records were retrieved from the databases. After removal of 459 duplicates, 965 records were put through title and abstract screening, which excluded 861 articles. After full-text assessment of the remaining 104 articles, 23 articles were included in the review (19 on factors related to vaccination uptake, and four on effectiveness of interventions for promoting vaccination uptake). Figure 2 illustrates the literature selection process.

Study Characteristics

The characteristics of the included articles are summarized in Supplemental Table 2, available online.

Studies on related factors

The 19 studies, pertaining to barriers and facilitators related to vaccination uptake among older adults, looked into attitudes, beliefs, and practices (including vaccination intent) regarding vaccines for COVID-19 (8/19 studies), influenza (3/19 studies), pneumococcal (3/19 studies), both influenza and pneumococcal (3/19 studies), pertussis (1/19 studies), and shingles (1/19 studies). There were more studies conducted in Australia (12/19 studies) than in Singapore (7/19 studies). In terms of study design, there were six retrospective data analysis studies, four cross-sectional studies, one cohort study, and eight qualitative studies.

Studies on intervention effectiveness

There were four studies that tested interventions aimed at increasing vaccination uptake among older adults. The vaccines of focus were influenza (2/4 studies), influenza and pneumococcal (1/4 studies), and shingles (1/4 studies). In terms of study design, two studies were randomized controlled trials, one was a before-and-after study, and one was a retrospective analysis. Three studies were conducted in Singapore and one in Australia.

Risk of Bias in Studies

Overall, the quality of the studies was found to be acceptable, except one, which was therefore removed from the review. The details on each study’s appraisal can be found in Supplemental Table 3, available online.

Factors Related to Vaccination Uptake

There are five factors related to vaccination uptake and they are as follows: individual characteristics, attitudes and beliefs, interpersonal, community, and vaccine-related. Under some of these factors, there are sub-factors. The factors or sub-factors are described as a barrier or facilitator depending on the outcomes of the specific studies included. More details of the barriers and facilitators pertaining to the factors can be found in Table 1.

Table 1.

Barriers and Facilitators Related to Vaccination Uptake Among Older Adults in Australia and Singapore.

Factor	Australia		Singapore		No. of studies (n = 19)
Factor	Barrier	Facilitator	Barrier	Facilitator	No. of studies (n = 19)
Individual characteristics
Age, years		Increasing age²⁶; aged 75-84²⁷; Qualitative findings:Aged ≥85 plus²⁸; those aged ≥70 were very supportive of vaccines²⁹		Aged ≥50³⁰	5
Sex		Men: SARSCoV-2 vaccine intention to uptake²⁶ Women: pneumococcal vaccine uptake^27,31 Women: herpes zoster vaccine uptake³²	Women: COVID-19³³		5
Knowledge and awareness of vaccine and immunization	Never having heard of the pneumococcal vaccine²⁷	Awareness of the eligibility of the free pneumococcal vaccination under the National Immunization Programme.²⁷ Qualitative findings:Awareness of the availability of vaccine for specific age groups of older adults³⁴	Qualitative findings:Misconceptions of influenza vaccines²³ Lack of knowledge about the influenza vaccine^35,36		5
Past vaccination experience or infection		Had influenza vaccination in the previous 12 months.²⁷ Qualitative findings:Having been immunized against pneumococcal disease²⁸ Experience of disease and vaccination over lifetime²⁹	Qualitative findings:The lack of experience with disease (ie, influenza)²³	Qualitative findings:Positive experience with influenza vaccine²³	4
Perceived health status			Poorer perceived health status^30,33,37	Positive perception of health status³³	3
Comorbidities		With comorbidities^27,31		Individuals with comorbidities³⁰	3
Income				High monthly household income^30,37	2
Marital status			Married³⁰	Separated, divorced, or widowed³⁷	2
Smoking status	Being a tobacco smoker²⁷	Being an ex-smoker³¹			2
Education				Higher education level (A-level/diploma/degree)³⁷	1
Employment status			Working in the past 12 months³⁰		1
Housing type				Lived in wealthier house types4- to 5-room flats or condominiums³³	1
Ethnicity			Indian³³		1
Engagement in physical activity				Sufficient total physical activity³⁰	1
Attitudes and beliefs
Perceived benefits of vaccine		Qualitative findings:Benefits of vaccination in relation to health and longevity^38,39 Individual and community protection^29,34 Having personal freedoms (eg, travel, socialize)^34,39		Qualitative findings:Belief that vaccines protect oneself from influenza infection²³; contains vitamins³⁵; belief that vaccination can lead to having a stronger body, being able to eat anything without fear of falling ill, and that prevention is better than cure³⁶	7
Perceived vaccine safety	Qualitative findings:Belief that vaccine is not safe^38,39 Fear of short- and/or long-term side effects³⁴		Qualitative findings:Worry of side effects and pain^23,35,36; Belief that vaccine could affect their ability to work⁴⁰; weaken bodies³⁶	Qualitative findings:Trust in vaccines’ safety²³	6
Social responsibility	Without regular contact with young children⁴¹; Being a health care worker²⁶	Close contact with children aged <5 years⁴¹ Qualitative findings:Concern for the health and livelihood of family members, and responsibility for the community in general²⁸ Protecting the public³⁹		Qualitative findings:Protecting loved ones²³	5
Trust	Distrust of vaccines (Trent et al)²⁷	Qualitative findingsLack of trust in governments³⁸	Qualitative findings:Mistrust in doctor’s advice^23,35	Trust in formal sources of information (eg, government sources and local news on television and on the radio³³	5
Perceived susceptibility	Low perceived susceptibility to disease²⁷	High perceived severity of disease²⁷; Perceived susceptibility to pneumonia²⁷ Qualitative findings:High perceived severity of disease²⁹	Qualitative findings:Perceived low risk of getting influenza²³	Qualitative findings:Perceived vulnerability was evidenced by frequent influenza episodes and the notion that a vaccine would reduce the severity of infection²³; belief that pneumonia is an illness that is more serious than influenza³⁶	4
Perceived effectiveness of vaccine		Positive perception of the effectiveness of vaccine^26,27,42			3
Personal health beliefs and practices	A preference to develop immunity ‘naturally’²⁷; Use of naturopath/herbalist or other alternative health practitioners⁴³; Practiced yoga often: influenza vaccination⁴³	Use of vitamins/minerals: at least sometimes or often⁴³	Qualitative findings:Dislike for taking any form of medication³⁵		3
Perceived severity			Qualitative findings:Belief that influenza is not a serious illness²³		1
Perceived importance of being vaccinated			Qualitative findings:There are other more pressing issues (eg, chronic health problems and work commitments²³		1
Religion			Qualitative findings:Religious objections³⁵		1
Fatalism			Qualitative findings:Perceived inevitability of illness in old age and belief in predestination²³		1
Interpersonal
Social influences	Qualitative findingsHealth practitioners acted as deterrents to vaccine uptake behaviors²⁸	Doctor’s recommendation²⁷ Qualitative findingsDoctor’s recommendation^28,34,39	Qualitative findings:Lack of advice and encouragement from health care workers^23,35; lack of encouragement from family members²³; vaccine was deemed unnecessary as surrounding vaccine uptake rates is low²³	Qualitative findings:Encouragement from friends and family^23,35,36; family and friends reminders²³; and encouragement from both doctors and nurses^23,36	8
Having a regular family doctor/GP				Having a regular family doctor/GP³⁷	2
Locality and access to vaccine
Locality	Living in low SES area^31,32	Living in higher socioeconomic status area²⁶			3
	General practices located in outer/remote/very remote areas^31,32	Vaccine coverage was highest in major cities³²			2
Access to vaccine		Easily available⁴²	Qualitative findings:Inconvenient to travel and long waiting hours at polyclinics³⁵		2
Vaccine-related
Vaccine procedure			Qualitative findings:Fear of injections^23,35		2
Cost			Qualitative findings:Expensive³⁶		1
Vaccine regulations				Qualitative findings:Complying with official recommendation to vaccinate before travel²³	1

Individual characteristics

The individual characteristics related to vaccination uptake among older adults included age, sex, knowledge and awareness of vaccine and immunization, past vaccination experience or infection, and perceived health status and comorbidities.

Age

Higher age was found to be a facilitator for vaccination uptake.²⁶ The prevalence of pneumococcal vaccination was greater among those aged 75 to 84 years compared with those aged 65 to 74 years,²⁷ whereas for influenza vaccination, those aged ≥65 years were significantly more likely to report influenza vaccination compared with those aged 50 to 64 years.³⁰ Older adults tend to be supportive of vaccines because they believe that they are more susceptible to diseases²⁸ and at risk for more severe diseases such as COVID-19.²⁹

Sex

Men were reported to be more likely to have a significantly higher SARSCoV-2 vaccine uptake intention compared with women.²⁶ Women were found to be less likely to have been vaccinated for SARSCoV-2 vaccine in Singapore.³³ For vaccines such as pneumococcal^27,31 or shingles³² vaccinations, women reported higher uptake compared with men in Australia.

Knowledge and awareness of vaccine and immunization

Knowledge was one of the most commonly reported factors related to vaccination uptake. The lack of knowledge about the influenza vaccine^35,36 and the lack of awareness about the pneumococcal vaccine²⁷ were barriers to the vaccine uptake among older adults. There were also various misconceptions about the influenza vaccine, such as it being only needed before travel, the interval for vaccination, vaccine as a cure or treatment for flu, the effect of aging on bodies making older adults not suitable for vaccine, that antibiotics could replace the need to have the influenza vaccine, and that proper lifestyle and diet are adequate to prevent getting flu.²³

Awareness of the types of vaccine available for their specific age group³⁴ and awareness of free vaccination²⁷ were facilitators for older adults to receive vaccination.

Past vaccination experience or infection

The lack of experience with influenza-influenced older adults to pay less attention to the need for influenza vaccination²³ was a barrier for the influenza vaccination uptake.

Having been vaccinated in the past was found to be a facilitator for vaccination uptake. Older adults who had received either an influenza vaccine in the previous 12 months²⁷ or a pneumococcal vaccine²⁸ were more receptive to vaccination. Previous experience of protective health effects of influenza vaccination for themselves and their families was also a predictor of influenza vaccination uptake.²³ Participants referred to their experience of disease, such as diphtheria, or having chronic diseases, or being immunocompromised, and having vaccination over their lifetime, when expressing their appreciation that the COVID-19 vaccine existed to reduce their vulnerability to the disease.²⁹

Perceived health status and comorbidities

Three Singapore-based studies reported that participants’ self-perceived health status was related to various vaccinations uptake, such as influenza, pneumococcal, and COVID-19. Perceived poor health was a barrier to the vaccinations, which resulted in lower uptake,^30,33,37 whereas perceived good health status was a facilitator related to higher vaccination uptake.³³

A significant factor positively related to vaccination uptake across both countries was existing comorbidities (such as lung disease).^27,30,31

Attitudes and beliefs

The attitudes and beliefs related to vaccination uptake were perceived benefits of vaccine, perceived vaccine safety and effectiveness, social responsibility, trust, perceived susceptibility, personal health beliefs and practice, and religion and fatalism.

Perceived benefits of vaccine

Another facilitator for older adults to go for vaccination was their perceived benefits of vaccines. Older adults reported the health benefits of vaccines in terms of protection of oneself²³ and the community from diseases,^29,34 and promoting longevity.^38,39 Older adults also reported a belief that vaccines contain vitamins³⁵ and can lead to a stronger body in terms of being able to eat without fear of falling sick.³⁶ Another perceived benefit of getting vaccinated was having the personal freedom to travel and socialize with others.^34,39

Perceived vaccine safety and effectiveness

A commonly reported barrier related to vaccination uptake was the belief that COVID-19 vaccines were not safe.^38,39 There are also studies that found that uptake is negatively related to fear of short- and long-term side effects of the vaccine,³⁴ and worry of pain associated with vaccination.^23,35,36

Older adults with perceptions that influenza vaccines are safe would go for vaccination.²³ Positive perception of the effectiveness of vaccine was reported as a strong facilitator for vaccination.^26,27,42

Social responsibility

In Australia, perceived social responsibility emerged as a barrier and facilitator to vaccination uptake. Older adults in close contact with children below five years of age reported highest recall rates of adult pertussis vaccination over time.⁴¹ Individuals also reported perceived social responsibility toward the community,²⁸ protecting the public and having a moral obligation to get vaccinated for the safety and protection of others, as a reason to opt for COVID-19 vaccination.³⁹

On the contrary, being an older adult without regular contact with young children was negatively related to pertussis vaccination uptake.⁴¹ In Singapore, older adults reported protecting their loved ones as a reason to receive influenza vaccination.²³

Trust

Studies reported levels of trust in vaccines, health care workers, and sources of information as related to vaccination uptake. In Australia, a general distrust of vaccines was a barrier to pneumococcal vaccine uptake,²⁷ with a lack of trust in vaccine development processes related to general distrust toward the government. There were misconceptions such as remote indigenous communities being used as test dummies for vaccines.³⁸ In Singapore, among the barriers to influenza uptake was mistrust in the doctor’s advice,²³ including their recommendations presumably being informed by profit considerations.³⁵

Trust in formal sources of information, such as government sources and local news on the television or radio, was a facilitator for older adults to get vaccinated.³³

Perceived susceptibility

A low perceived risk and severity of disease was a barrier to vaccination uptake.²⁷ In Singapore, a low perceived risk of contracting influenza, reinforced by previous experience of mild episodes of influenza, influenced older adults to not get influenza vaccinations.²³ Thus, older adults were less willing to get vaccinated if they did not see the disease as a threat.

Conversely, high perceived severity of disease and a belief that an existing health condition would increase the risk of pneumonia was a facilitator for pneumococcal vaccination uptake.^27,29,36

Personal health beliefs and practices

In Australia, older adults, who preferred to develop immunity “naturally,”²⁷ consulted alternative health practitioners, such as naturalists or herbalists, and practiced yoga, often were less likely to receive vaccination.⁴³

Taking vitamins and minerals, however, was positively related to uptake.⁴³ In Singapore, those who indicated a dislike of taking any form of medication reported low vaccination uptake.³⁵

Religion and fatalism

Among older adults in Singapore, having the belief that illness in old age is inevitable, belief in predestination,²³ and religious objections³⁵ were among the barriers to getting influenza vaccinations.

Interpersonal

The interpersonal factors related to vaccination uptake among older adults included social influence and having a regular family doctor/general practitioner.

Social influence

Studies found that recommendations by physicians and other health care personnel, as well as family members, were related to vaccination uptake. Social influences came in the forms of recommendations by doctors and nurses, or personal recommendations by friends and family. In both Australia and Singapore, a lack of advice and encouragement from health care workers was a barrier to vaccination uptake.^23,28,35 In Singapore, a lack of encouragement and reminders from immediate social networks, such as friends and family, was another barrier for not going for influenza vaccination.²³

Studies showed a positive relationship between family and friends’ recommendations and the decision to receive vaccination.^23,35,36 Recommendations from health care workers was a facilitator for vaccinations uptake across both countries.^27,28,34,39

Having a regular family doctor/general practitioner

In Singapore, the likelihood of being vaccinated was higher among older adults who reported having a regular general practitioner or doctor.^30,37

Locality and access to vaccine

The locality factors were related to locality and access to vaccine.

Locality

In Australia, pneumococcal vaccination uptake was lower among patients whose general practitioner’s clinic was located in outer and remote areas, compared with inner regional or major cities.³¹ Vaccination coverage among older adults varied by remoteness and was highest in major cities.³² Living in a higher socioeconomic status area was a facilitator for vaccination uptake,²⁶ whereas living in lower socioeconomic status areas^31,32 was found to be a barrier.

Access to vaccine

Access to vaccines was a predictor of uptake in both countries.^35,42 In Singapore, older adults reported that the need to travel to vaccination sites and the long waiting times at clinics as inconveniences that deterred them from influenza vaccination.³⁵

Vaccine-related

Cost

The high cost of vaccine was reported as a barrier for vaccine uptake in general.³⁶ A fear of injections prevented some older adults from receiving vaccination.^23,35

Vaccine regulations

Complying with pretravel vaccination regulation was a facilitator related to higher influenza vaccination uptake among Singapore older adults.²

Effectiveness of Interventions for Promoting Vaccination Uptake

Three interventions for promoting vaccination uptake were reported, namely, using financial strategies, supporting clinicians, and engaging consumers.

Engaging consumers

The intervention of engaging consumers through provision of informational flyers and posters was found to have mixed effectiveness.^40,44 Nurse reminders for patients to go for vaccination can also increase vaccination uptake.⁴⁴

Support clinicians

Interventions that focused on supporting doctors, such as creating awareness on the low baseline vaccination rates among older adults,⁴⁴ and facilitating doctors in providing structured health assessment,⁴⁵ led to vaccination uptake among patients.

Use financial strategies

Although financial strategies such as providing monetary incentives (SGD20 = US$14.70) could improve influenza vaccination uptake, increasing the amount (to SGD30 = US$22) was reported to be ineffective. However, this finding was reported to be different for older adults who were working and not working, with the former not sensitive to the increased amount offered, given the time barrier to go for vaccination.⁴⁶ Table 2 provides an overview of the interventions and their effectiveness.

Table 2.

Effectiveness of Interventions for Promoting Vaccination Uptake Among Older Adults.

Intervention category (intervention description)	Effective	Not effective	No of studies (out of 4)
Engage consumers (involving, preparing, and intervening with patients and the market to involve them and increase demand for the clinical innovation)	Patients who visited the clinic during the intervention (informational flyers and posters) period were more likely to receive influenza vaccination (aOR = 1.43; 95% CI [0.99, 2.07]; P = .06) than were those who visited during the control period. They were also more likely to receive pneumococcal vaccination (aOR = 1.78; 95% CI [1.28, 2.48]; P < .01).⁴⁰ An additional 34 patients (12.1%) received their vaccinations as a result of nurses’ reminders^44a	None of the patients attributed their updated vaccination status to the patient education posters.^44a	3
Support clinicians (supporting clinical staff performance)	When structured health assessments were provided, patients eligible for free vaccine were more likely to receive a zoster vaccine (adjusted OR = 3.0; 95% CI [2.8, 3.2]) than in encounters where this health assessment was not provided.⁴⁵ Although the vaccination card reminders on the computers and the newly minted electronic health record system influenced practices, the main impetus for change was the realization that current vaccination rates were low (intervention: department briefing to the physicians was conducted, highlighting the baseline influenza vaccination rates.⁴⁴		2
Use financial strategies (changing the patient billing systems, fee structures, reimbursement policies, research funding, and clinician incentives)	Increasing the total monetary incentive for vaccination and reporting from SGD10 to SGD20 increased participation in vaccination from 4.5% to 7.5% (P < .001)⁴⁶		1

The study by Li et al, 2019, is a multifaceted intervention study that comprised several discrete strategies, including education posters, vaccination card reminders, utilizing electronic health care record system, department briefing to the physicians, and nurse reminders. Overall, the entire intervention was effective at improving vaccination (baseline influenza vaccination rate among the preintervention group was 47.7% (166 out of 348 patients). In the post-intervention group, the influenza vaccination rate improved significantly to 80.7% (281 out of 348 patients) (P < .001).⁴⁴

Abbreviations: aOR = adjusted odds ratio; CI = confidence interval.

Discussion

This rapid review presents a thorough overview of barriers and facilitators influencing uptake of vaccinations among older adults, aged 50 years and older, in Australia and Singapore. The more prevalent factors influencing vaccine uptake among older adults found in this review were related to interpersonal (social influences), attitudes (perceived benefits of vaccine, perceived vaccine safety, social responsibility, and trust), and individual characteristics (age, sex, and knowledge and awareness of vaccine and immunization). Apart from this, interventions that were found to be effective in improving vaccine uptake were also reported and these were to engage consumers, support clinicians, and use financial strategies.

The majority of the findings of this review are similar to two reviews conducted among older adults in Western societies (Europe and North America), where income, education level, living in deprived areas,⁴⁷ attitudes and beliefs regarding vaccination, HCPs’ and family and friends’ influences, vaccine’s side effects and effectiveness, and perceived susceptibility²² were found to be key factors influencing vaccine uptake. This indicates that many of the factors influencing vaccine uptake among older adults are universal among high-income countries that have clear guidance on these vaccines in their national immunization schedules. Australia and Singapore provide vaccines at subsidized rates or at no cost to older adults. Australia’s National Immunization Program also provides clear guidance for adult vaccines. Under the program, free vaccines are provided for adults and seniors. These include pneumococcal, influenza, and shingles vaccines.⁴⁸ As a result, 58.0% of the population aged 65 years and older were vaccinated against seasonal influenza in 2019.⁴⁹ In 2017, Singapore’s National Adult Immunization Schedule (NAIS) was introduced to provide guidance on 11 important vaccinations for adults. MEDISAVE, the national medical savings scheme, can be used to pay for vaccinations recommended under the NAIS.⁵⁰ Since the introduction of this scheme, around 24% of adults aged between 65 and 79 years took up the vaccinations.⁵¹ Singapore is currently implementing a new strategy aimed at healthy aging in 2023, which will provide full subsidies for vaccines for older adults.⁵²

The finding of this review adds to the body of literature on effective interventions in increasing vaccination uptake rates among countries in the Asia-Pacific region,¹⁴ and found that informational flyers and posters, nurse reminders, highlighting the baseline influenza vaccination rates among HCPs, and having structured health assessments could increase vaccination uptake. The barriers and facilitators identified in this study, such as perceived benefits of vaccine, perceived vaccine safety, trust, and knowledge and awareness of vaccine and immunization, indicate that investing in educational interventions is the key to promote vaccination uptake among older adults in Australia and Singapore. Other educational interventions, such as pharmacist-led interventions, have been shown to be effective in increasing vaccination uptake.^53,54

In this review, social influences was the most commonly reported factor influencing vaccine uptake among older adults. The HCPs, family, friends, and the community can affect an older adults’ decision on whether to go for vaccination. In the Asian setting, this is not surprising as older adults tend to defer their health decision-making to their children or physicians, whom they see as more knowledgeable.⁵⁵ Interventions to promote vaccine uptake that leverage on social influences should be developed, especially getting HCPs to encourage older adults to go for vaccinations. This review highlighted that nurse reminders was effective in getting older adults to go for vaccination.⁴⁴ The HCPs’ recommendation has consistently shown to be the strongest motivator to encourage vaccination.^22,56,57 However, HCPs faced a myriad of challenges to offer vaccination.⁵⁸ Interventions, such as provider education with or without the support of a designated vaccination champion, implementation of a recall/reminder through clinical decision support system, or collaboration through public-private collaboration were reported to be effective solutions to address HCPs’ challenges to offer vaccination.⁵⁹ This review also highlighted that having structured health assessment for HCPs was effective in getting older adults to go for free vaccination.⁴⁵

One of the lesser reported factors influencing vaccination uptake in the literature is religion. In the review by Jain et al,⁴⁷ religion as a factor influencing vaccine uptake was only studied in two articles in which both showed inconsistent findings. In this review, religious objection was reported as a barrier to influenza vaccine uptake in a Singapore study. In the Asia-Pacific region, where Hindus, Muslims, and Buddhists formed the larger religious groups in the region, religion plays an important role in influencing one’s way of life, including health decision-making, such as vaccination uptake. The more prominent religious barriers to vaccinations were related to concern with the ingredient content of vaccines for Muslims, and religious taboos in Hinduism and Sikhism.⁶⁰ Religion tends to become more important as an individual gets older⁶¹ and, given the increasing aging population in various countries in Asia-Pacific region, such as Singapore, more studies are needed to determine whether religion is a determinant to vaccination uptake among older adults.

Strengths and Limitations

This review is the first that provides an overview of barriers and facilitators, and effective interventions that can promote vaccine uptake among older adults in the Asia-Pacific setting. Despite being a rapid review, the process of appraising the quality of the studies to be included in the review was conducted to ensure quality studies were included. The findings of this review need to be interpreted with caution. First, the studies within this review were only from Australia and Singapore. Only two databases were used, and only five years were applied when searching for relevant literature. This could have led to the lack of comprehensiveness in the search that might have resulted in missed studies. This might also be the reason why studies from Indonesia and Philippines were not found. Second, only studies in English were included, resulting in the exclusion of other data.

Conclusion

This review highlighted the major factors influencing older adults’ uptake of vaccination in Australia and Singapore, and they were social influences, perceived benefits of vaccine, perceived vaccine safety and effectiveness, social responsibility, trust, age, sex, and knowledge and awareness of vaccine, and immunization. Although interventions, such as engaging consumers, supporting clinicians, and financial incentives were found to be effective, interventions that target the major influencing factors identified should also be considered.

Supplemental Material

sj-docx-1-aph-10.1177_10105395241258530 – Supplemental material for Factors Related to, and Effective Interventions for, Vaccination Uptake Among Older Adults in Two Asia-Pacific Countries: A Rapid Review

Supplemental material, sj-docx-1-aph-10.1177_10105395241258530 for Factors Related to, and Effective Interventions for, Vaccination Uptake Among Older Adults in Two Asia-Pacific Countries: A Rapid Review by Wen Ting Tong, Ananta Seth, Mary Pei Ern Ng, Shao Chuen Tong, Amanda Lau, Tina Yen-Ting Chen, Suan Ee Ong and Joanne Su-Yin Yoong in Asia Pacific Journal of Public Health

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Wen Ting Tong

Supplemental Material

Supplemental material for this article is available online.

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