1. Introduction

A delay or refusal to get vaccinated despite the availability of vaccines, also known as vaccine hesitancy, is considered one of the top ten threats to global health by the World Health Organization (WHO) [1]. Reasons for hesitancy are complex and are driven by both an individual’s perceptions and attitudes towards a particular vaccine or vaccines in general, their sociodemographic characteristics (e.g. gender, ethnicity) and contextual factors (e.g. trust in experts, perceived risk) [2]. The indecision and uncertainty about vaccination are amenable to change should emerging concerns be addressed adequately [3]. The importance of understanding the factors driving vaccine hesitancy has become increasingly apparent throughout the current global outbreak of coronavirus disease 2019 (COVID-19). As COVID-19 spread around the globe and the number of active infections and death tolls increased, the need for a vaccine to fight the pandemic became increasingly more critical. However, the rapidity of vaccine development and approval and concerns regarding the vaccine’s safety, effectiveness and side effects have contributed to a lack of vaccine confidence and lower vaccination uptake rates in the general population [4].

Research has identified that healthcare workers (HCWs) and healthcare students are one such sub-group which are displaying considerable hesitancy towards accepting a COVID-19 vaccine. For example, a review exploring the prevalence of hesitancy in more than 75,000 HCWs worldwide found that a fifth of professionals were reluctant to accept a COVID-19 vaccine [5]. For healthcare students, rates of hesitancy were found to mimic those of practising professionals, whereby nearly a fifth of healthcare students (~20,000 students across 39 countries) were also hesitant to accept a COVID-19 vaccination [6]. The high rates of hesitancy in this population are of significant concern for several reasons. Firstly, HCWs and healthcare students are at an increased risk of contracting the virus, which would result in greater staff absence at a time when healthcare is in greater demand [7]. Secondly, HCWs and healthcare students are more likely to be a vector of the virus, transmitting infections to clinically vulnerable patients, the elderly, family members and colleagues, increasing active infections [8]. Furthermore, vaccination recommendations from HCWs have been shown to increase vaccine acceptance in the general population [9, 10]. Therefore, understanding the factors contributing to vaccine hesitancy and implementing effective strategies to tackle this problem is pivotal in reducing the transmission of COVID-19, increasing vaccination uptake in the general population, and maintaining a safe healthcare provision. Over the last 18 months, there has been a rapid growth of primary studies exploring factors associated with COVID-19 vaccine hesitancy for this population in various countries worldwide. As a result, numerous systematic reviews and meta-analyses have also been conducted between the years 2020 and 2022. However, these reviews failed to provide conclusive and univocal evidence on the COVID-19 vaccine acceptance rate, by reporting a variation from 41.84% [29] to 80.41% [45] in HCWs and from 53.85% [29] to 82.37% [35] in healthcare students. Moreover, when systematic reviews and meta-analyses on the same topic are conducted and published in the same years, there is a greater risk of inconclusive results, which, therefore, may have consequences for the clinical decision-making process at both individual and organizational levels. As intervention strategies depend upon this evidence, despite the several reviews published on the topic, there is a need to compile evidence from previously published systematic reviews and meta-analyses to provide an overview of the topic. Therefore, an Umbrella Review will be undertaken to synthesize evidence on the factors associated with hesitancy and acceptance of the COVID-19 vaccine for HCWs and healthcare students. Additionally, suggestions to address the identified drivers will be discussed.

2. Methods

A systematic literature search was performed and reported in accordance with the Joanna Briggs Institutes (JBI) guidelines for Umbrella Reviews [11]. The Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines were utilised to report the results [12]. A protocol was registered with PROSPERO prior to the commencement of the review (registration no: CRD42022327354). The search strategy and syntax were peer-reviewed by an expert librarian using the Peer Review of Electronic Search Strategies (PRESS) checklist [13] and modifications were implemented prior to the commencement of searches.

2.1 Eligibility criteria

The inclusion and exclusion criteria are outlined in Table 1. Studies were eligible for inclusion if they: (i) conducted a systematic review (with or without meta-analysis); (ii) included primary sources utilising a quantitative methodology; (iii) investigated factors related to COVID-19 vaccine hesitancy or vaccine uptake; (iv) included a population or subpopulation of HCWs or healthcare students aged between 18–65 years; (v) were published after 2019 (due to the nature of the topic); (vi) and published in the English language. This review will include peer-reviewed and pre-printed material due to the fast nature of the research surrounding the COVID-19 pandemic. Other non-peer-reviewed material will be excluded (e.g. letters to editors, opinion pieces, commentaries).

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Table 1. Inclusion and exclusion criteria for eligibility in the review.

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2.2 Information sources and search strategy

A systematic search was conducted on the following databases: CINAHL, Cochrane Library, PubMed, ProQuest (COVID-19 Database and International Bibliography of Social Sciences (IBSS)), ScienceDirect, Web of Science, Google Scholar and Epistemonikos. Databases were searched from November 2019 up to 23^rd May 2022. The search syntax (Table 2) was entered into the databases as free text rather than MeSH terms. Boolean operators and truncation were utilised if supported by the database. The reference lists of included papers were hand-searched to identify citations not retrieved in the initial searches.

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Table 2. Search syntax used to search databases.

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3. Results

3.1 Selection of included studies

The search strategy generated 12,774 citations, of which 11,191 were unique. Following title and abstract screening, 11,125 citations were eliminated as they did not meet the initial inclusion criteria. Full-text screening was conducted on 66 papers and 39 were excluded. Main reasons for exclusion were that the review did not include populations of interest (e.g. HCWs or healthcare students), vaccination of interest (e.g. COVID-19), outcomes of interest (e.g. barriers of facilitators of vaccine hesitancy) or were of an unsuitable publication type (e.g. letters to editors, commentaries). Hand-searching the reference lists of the 27 eligible reviews identified 15 citations of interest; however, after full-text screening, only 1 citation was eligible for inclusion. Monitoring of database search alerts for 30 consecutive days identified an additional three eligible articles. A total of 31 reviews met the inclusion criteria and were included (Fig 1).

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Fig 1. PRISMA flowchart [12] detailing the identification and selection of research syntheses for inclusion in the Umbrella Review.

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3.2 Characteristics of included studies

Characteristics of the included reviews are outlined in Table 3. Of the 31 reviews included, 27 were published as peer-reviewed journal articles, three were published on pre-print servers [20–22] and one was a peer-reviewed pre-proof [23]. There were eight systematic reviews and meta-analyses [24–31], 16 systematic reviews [20, 21, 32–40] (five categorised as rapid [41–45]), six scoping reviews [5, 22, 46–49] and one integrative review [23]. All reviews included quantitative, cross-sectional primary studies, while three included longitudinal study designs [32, 35, 45] and one included mixed-method surveys [45]. Nineteen reviews were published in 2021 and 12 in 2022, which captured primary studies published from February 2020 to August 2021 [31]. Nine reviews were published in Asia (China [26, 28, 42], Jordan [32], Thailand [33], Malaysia [27], Bangladesh [29], Pakistan [40], Iran [41]), eight in the USA [5, 23, 30, 36, 43, 45, 47, 48], seven in Europe (Italy [35, 38], The Netherlands [22, 49], Greece [25], Czech Republic [37], Slovakia [31]), six in Africa (Ethiopia [21, 34, 39], Ghana [24], Nigeria [44], Burkina Faso [20]) and one in Canada [46]. Of the 31 reviews, 14 assessed the methodological quality of the primary studies included in their review. Commonly used appraisal tools were the JBI critical appraisal tool for cross-sectional studies [25, 27, 29, 30, 42] and the Newcastle-Ottawa scale (NOS) for cross-sectional studies [21, 24, 26, 39]. Where used, a large proportion of the primary studies were assessed as ‘high to moderate quality’ (JBI tool) or as ‘low to moderate risk of bias’ (NOS tool).

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Table 3. Main characteristics of studies included in the Umbrella Review.

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3.3 Characteristics of participants

The sociodemographic characteristics of the populations included in the reviews are outlined in Table 4. Nine reviews focused on HCWs [5, 22–25, 28, 34, 42, 48], three reviews focused on healthcare students [26, 27, 31] and 19 included a mixed population either containing a subset of HCWs [21, 30, 32, 33, 41, 43, 44, 47, 49] or subsets of both HCWs and healthcare students [20, 29, 35–40, 45, 46]. There was large variability in occupational roles reported for the HCWs, but Physicians, Nurses, Dentists, Pharmacists, Midwives, Physiotherapists and General Practitioners were the most commonly cited occupational roles across the reviews. The most frequently reported trainee courses for healthcare students were dentistry, nursing and medicine. The total sample size (where reported) for HCWs was 639,699 (Range = 1941–76,741) and for healthcare students the total number of participants was 70,711 (Range = 934–19,123). Of the 11 reviews reporting sex distributions, all 11 reported a female predominance (>50%) of participants in their primary studies [23–27, 33–35, 38, 40, 48].

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Table 4. Sociodemographic characteristics of populations included in the Umbrella Review.

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3.6 Findings of the review

3.6.1 Vaccine acceptance rates.

Vaccine acceptance rates (as a pooled average) were reported in 19 studies [5, 23–31, 35–37, 39, 41, 45, 46, 48, 49] (Table 4). For HCWs, acceptance rates ranged from 20.7% [48] to 81.1% [27]. When broken down by occupational role, Nurses (Pooled average range = 20.7%-40%) and Allied health professionals (Pooled average = 31.6%) had the lowest acceptance rates. In contrast, Dental practitioners (Pooled average = 81.1%), Direct medical providers (Pooled average = 80.4%) and Physicians (Pooled average = 80%) had the highest acceptance rates. For healthcare students, acceptance rates ranged from 34% [24] to 82.4% [35]. Nursing and Dental students both had an acceptance rate of 60% [26].

3.6.2 Determinants of vaccine hesitancy for HCWs.

The factors associated with vaccine hesitancy and vaccine acceptance for HCWs are displayed in Table 5.

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Table 5. Factors associated with vaccine hesitancy and vaccine acceptance for HCWs.

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Vaccine-related factors: HCWs who had concerns regarding the adverse long-term side effects of the vaccine [5, 20, 22, 24, 32–34, 36, 40, 42, 46–49], as well as concerns about the tolerability of vaccine side effects [20] and its impacts on fertility [48] were more hesitant to accept a COVID-19 vaccine. As were those who had concerns about the safety [5, 22–24, 30, 32–34, 36, 38, 42–48], quality [33, 47, 48] and effectiveness or efficacy [5, 20, 22, 24, 30, 32, 33, 36, 38, 42–48] of COVID-19 vaccines. Alternatively, HCWs who displayed less concern for serious vaccine side-effects [36] and perceived the vaccine to be safe [20, 34, 39, 48, 49] and effective [20, 21, 32–34, 36, 46, 48] were more accepting of a vaccine. Greater hesitancy was also shown by individuals who had concerns about the rapid development [5, 22, 33, 41, 42, 48, 49] and approval [42, 48] of COVID-19 vaccines, as well as the short duration of clinical trials [20, 24, 33, 34, 48]. Moreover, distrust of the expedited vaccine production, healthcare policies and regulatory policies [34, 42] and perceived politicisation of the vaccines [5, 23, 42] were associated with greater hesitancy in HCWs. Individuals who had confidence in the vaccine development process [48] and trusted the vaccine manufacturing country [33] were more likely to accept a COVID-19 inoculation. Hesitancy was also associated with concerns regarding the financial cost of the vaccine [33] and concerns regarding vaccine storage [36]. A lack of payment [34] and easy logistics to get vaccines [34] was associated with greater vaccine uptake. HCWs who perceived more vaccine benefits [5, 36, 39, 45, 48] were more accepting than those who perceived a lack of benefits [36, 48]. Individuals who perceived greater risks, such as contracting COVID-19 infection from the vaccine [24, 30, 33, 48], were more hesitant to accept an inoculation.

Information and sources: HCWs who perceived a lack of information about the vaccine [22, 24, 33, 36, 42, 48] and its side effects [24] exhibited more hesitancy towards a COVID-19 vaccine. As did those concerned about a lack of scientific information [48] or perceived a lack of adequate information available to support an informed decision [48, 45]. HCWs with a lack of knowledge about COVID-19 [48] and COVID-19 vaccines [33, 48] were more hesitant than HCWs who had sufficient knowledge about COVID-19 [5, 21, 48] and COVID-19 vaccines [25, 48]. HCWs who utilised social media [30] or non-authentic information sources [48] were more hesitant than HCWs who retrieved their COVID-19 related information from scientific literature [36], health authorities and associated websites [34, 36, 39, 49], national or local TV [45], national newspapers [45], Facebook [21, 34] or other reliable sources of information [48]. Exposure to misinformation about COVID-19 and the vaccines on social media was associated with vaccine hesitancy [5, 22, 24, 32, 33, 36, 44, 48]. Similarly, receiving conflicting or unclear information about COVID-19 [30] and its side effects [48], especially by public health authorities [20], was also found to contribute to vaccine hesitancy.

Health factors: HCWs who had not previously contracted a COVID-19 infection were more accepting of a COVID-19 vaccine [5, 48]. However, a history of COVID-19 infection was associated with both vaccine hesitancy [5, 34, 45, 47, 48] and acceptance [20, 22, 25, 39, 45, 48]. Having a chronic health condition was both a determinant of vaccine hesitancy [5, 23, 36, 42, 45, 48] and acceptance [5, 21, 22, 25, 32, 34, 38, 39, 42, 43, 46–48]. Individuals with no chronic health conditions [48] were more likely to accept a COVID-19 vaccination. HCWs who had previously accepted an influenza vaccination [5, 21, 25, 28, 30, 32–34, 36, 38, 39, 42, 43, 45–48] or other inoculations [5, 22, 25, 29, 30, 34, 39, 46, 48] were more likely to accept a COVID-19 vaccine than HCWs who had not accepted an inoculation [23, 43] such as the influenza vaccine [22, 29, 34, 36, 45] previously. Fear of injections was also associated with hesitancy [33, 48]. An individual’s smoking status [21, 45, 48], allergen history [21, 34, 48], BMI status [45] and depression history [26, 34] were all factors associated with vaccine acceptance. Individuals who were pregnant [33, 45] or trying to conceive [45] were hesitant to accept a COVID-19 inoculation.

Sociodemographic factors: This review found that gender [21, 45], specifically, male [5, 22, 23, 25, 28–34, 36, 38–40, 42, 43, 46, 47] and non-binary female [23] was associated with vaccination acceptance. Being female was found to be both a barrier [22, 23, 34, 36, 40, 43, 45] and facilitator [20, 23, 29, 34, 36, 48] of vaccine uptake. An individual’s ethnicity/race [20, 21, 45] contributed to vaccination intentions. In particular, White ethnicity/race [5, 23, 25, 45, 48] (including White/Asian race [5, 34, 39, 42] and Non-Hispanic White [40]) was associated with vaccine acceptance, while Black ethnicity/race [30, 34, 45] (including Black and Hispanic [23, 42], Non-Hispanic Black [45] and Black/African American [40] ethnicities) was associated with vaccine hesitancy. Asian ethnicity was found to be both a barrier [23, 45] (including Asian and Latino [45] and Non-Hispanic Asian [45] ethnicities) and a facilitator [23] of vaccine acceptance. Latinx ethnicity [34] (including Hispanic/Latinx [45] ethnicities) was also associated with vaccine hesitancy. Both younger (<40) and older age (>45) were associated with vaccine hesitancy [20, 22, 25, 36, 45] and acceptance [5, 20–23, 25, 28–30, 32–34, 36, 39, 42, 43, 45–48]. Higher educational attainment [5, 22, 25, 30, 34, 36, 39, 42, 45, 48] was associated with vaccine acceptance and lower educational attainment with vaccine hesitancy [23, 32, 36, 45, 48]. Increased or higher income [5, 25, 34, 39, 42] and lower income [20, 48] were associated with vaccine acceptance and hesitancy, respectively. HCWs residing in upper-middle and lower-middle countries [27], or the Democratic Republic of Congo [35], Southeast Asia [27], Europe [27] and South Africa [36] were more likely to be hesitant towards a COVID-19 vaccine than HCWs residing in high-income countries [27], Eastern Asian countries (China, India, Republic of Indonesia, Singapore, Vietnam and Bhutan) [35] and Middle East countries [27]. Residing in the USA was a barrier [35] and facilitator [42] of vaccine acceptance. HCWs who were married [20, 48] were more accepting of a COVID-19 vaccine than those who were single [20]. Having a child or children was a barrier [47] and a facilitator of vaccine acceptance [36, 48]. An individual’s religious or political beliefs could be both a barrier [22, 42, 48] and a facilitator [5, 22, 34, 42, 45, 48] of acceptance of a COVID-19 vaccination.

Occupational factors: Vaccine acceptance was associated with working in public/government institutes [29], a medical faculty [42], or in the healthcare profession [21, 22, 32–34, 36, 39, 43, 45, 46, 48]. In particular, Physicians [20, 22, 23, 25, 32, 34, 36, 41–43, 46], General practitioners [46], Pharmacists [45], prescribing Physicians [23, 42, 45], Emergency department/room workers [48], Clinical or frontline workers [5], Dentists [25, 29], Dental practitioners [27], Rehabilitation centre workers [34], non-MD health professionals [21, 34], Scientists [41] and Research scientists [42] displayed more vaccine acceptance. Whereas Nurses [20, 22, 23, 25, 29, 33, 36, 41, 45, 46], assistant nurses [46], Paramedical staff [25], Allied health professionals [20, 41, 45], Trainees [45] and those in non-clinical roles [45] were found to be more hesitant towards a COVID-19 inoculation. HCWs involved in COVID-19 duties (e.g. caring for COVID-19 patients [29, 32, 39, 41, 42, 48], working in a designated hospital [34]) and were exposed to COVID-19 through patient [5, 25, 34, 39, 42, 47] or colleague interactions [42] were more likely to accept a COVID-19 vaccine. Contrastingly, individuals who did not care for COVID-19 patients [32, 41] were more hesitant. HCWs who displayed unfavourable attitudes towards workplace infection control policies [30, 46] and a lack of personal protective equipment (PPE) [46] were more accepting of a vaccine than those HCWs who were satisfied with workplace PPE [48]. Attitudes toward compulsory vaccination for HCWs were both a barrier [33, 36] and facilitator [21, 22, 32, 36] of vaccine uptake, depending upon an individual’s level of agreement. Retired [32, 43] and hourly paid HCWs [45] were less accepting of a vaccine. HCWs unemployed due to COVID-19 were more accepting of a vaccine [36, 39, 41, 43].

Trust factors: HCWs that had a lack of trust in key social actors, such as the government [23, 24, 30, 36, 42, 48], vaccine manufacturers [23, 24, 33, 48], pharmaceutical companies [5, 20, 48], health authorities [5, 30, 42, 48], health experts [5, 30, 36, 42] and scientists [48] were more hesitant to accept a COVID-19 vaccine. Whereas HCWs that had higher levels of trust in these social actors, as well as non-health leaders [48], mass media [32], science [25, 48] and public health websites or providers [48], were more accepting of inoculation. Additionally, higher levels of trust in pandemic management [20, 21, 34] and health promotion strategies [36] were associated with vaccine acceptance. Individuals with a lack of trust or confidence in vaccines [48] and their safety [36] displayed more hesitancy than individuals that were more trusting of vaccines [5, 25, 46, 48].

Belief factors: Individuals that perceived themselves to be at higher risk of contracting a severe COVID-19 infection [5, 20, 25, 30, 32–34, 36, 39, 41–43, 45–48] were more accepting of a vaccination than those perceiving themselves to be less susceptible [20, 23, 43, 48] or less concerned with contracting COVID-19 [36, 42, 45]. HCWs that had negative perceptions regarding COVID-19, for example, that the disease does not exist [5], that symptoms are mild [20, 30, 33, 48] and a vaccine is not necessary [32, 38, 42, 43, 46–48], were also more hesitant to accept a COVID-19 inoculation. As were those who held anti-vaccination beliefs [22, 46, 48] and preferred natural immunity [29, 33, 42, 48] or other COVID-19 preventative measures [48]. Alternatively, individuals with positive perceptions of COVID-19 [32, 46] and the benefits [5, 20, 39, 45], safety [20, 29] and efficacy [20, 48] of a COVID-19 vaccine [5, 25, 36, 39, 42, 48] were more likely to accept an inoculation. HCWs that perceived COVID-19 to be a serious disease [5] and believed in the importance of pandemic management strategies, such as compulsory vaccination for the public [29, 34], isolation as an effective transmission reduction strategy [46] and had confidence in and expectations about PPE and other preventative behaviours [24, 45] were more accepting of a COVID-19 vaccine.

Emotional factors: Higher levels of negative emotional responses (e.g. anxiety, doubts, fear and worry) were found to be a driver of vaccine hesitancy for some individuals [24, 30, 44, 48] and vaccine acceptance for others [5, 22, 25, 26, 32, 34, 36, 39, 42, 46].

Social factors: Individuals who expressed high levels of altruism towards protecting others [32, 45, 48] or perceived vaccination as a collective responsibility [5, 22, 25, 39, 46, 48] were more likely to accept an inoculation. HCWs concerned about transmitting COVID-19 to family members, relatives or friends [5, 22, 26, 34, 48], or those who lived with elderly relatives [5, 25, 36, 48] or vulnerable individuals [5, 21, 25, 36, 48] were more accepting of a COVID-19 vaccine. As were those individuals who had a family member or friend who had been diagnosed with [20, 22, 48] or had died from COVID-19 [20, 45, 48]. Vaccination recommendations from healthcare professionals [29, 48] or encouragement from social networks [5, 33, 36, 48], experts [36], or news media [36] all contributed to vaccine acceptance. In contrast, individuals experiencing less social pressure were more likely to be hesitant to accept an inoculation [48]. Similarly, individuals were more likely to be hesitant if they had been exposed to anecdotes regarding negative reactions to a COVID-19 vaccination [20].

Behavioural factors: HCWs who exhibited proactive behaviours, such as engaging in preventative behaviours [34] and testing procedures [34, 39], were more accepting of vaccination, as were those who recommended the vaccine to parents [34], elderly individuals [34] and the general population [5, 29] and had dispensed the inoculation to their children [34]. Individuals more accepting of a COVID-19 vaccine were more likely to do so to inspire confidence in vaccine safety [45] and contribute to herd immunity [45].

Environmental factors: Vaccine acceptance was associated with the severity of the local epidemic situation and local COVID-19 mortality figures [48]. HCWs who were hesitant to accept the vaccine reported a lack of time to seek out vaccination [32, 42, 43, 47, 48] or make a decision [34] and preferred to wait until others had received the vaccine first [33, 34]. An initial delay in accepting a vaccine was also associated with vaccine acceptance at a subsequent timepoint [35].

3.6.3 Determinants of vaccine hesitancy for healthcare students.

The amalgamation of results from the ten reviews that included populations of healthcare students found various factors associated with hesitancy or acceptance of a COVID-19 vaccine (Table 6).

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Table 6. Factors associated with vaccine hesitancy and vaccine acceptance for healthcare students.

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Sociodemographic factors: This review found that female students [31] were more hesitant than male students [20, 21, 29, 45, 46]. Although, one review reported that being female was a factor associated with acceptance [39]. With regards to ethnicity, Black/African American students [40] displayed more hesitancy towards the vaccine than non-Hispanic White students [40] or those from underrepresented minorities [45]. Additional sociodemographic factors associated with vaccine acceptance in this population were older age [40, 45, 46], having a higher income [36], higher socioeconomic status [36] or whose marital status was single [20, 29, 39]. Vaccine acceptance was lower in students residing in Egypt [35] and higher in students residing in the USA [35].

Educational factors: Dental students [40] and non-medical students [35] exhibited more hesitancy, whereas pharmacy students [29], medical students [35, 40] and both healthcare and non-healthcare students [46] were more accepting of a vaccine. Other vaccine-accepting populations were academics, students, support staff [46] and individuals working in a medical faculty [46]. Additionally, students in their first or second year of study [31] were more hesitant than students in their third year (or above) of study [21, 29] or were graduate students [29, 45]. Healthcare students who disagreed with compulsory vaccination for healthcare professionals were more hesitant than those in support of a compulsory COVID-19 vaccine [26, 31].

Health factors: Perceptions of good health were found to determine vaccine hesitancy [46] and acceptance [29]. Alternatively, students with a history of previous illnesses [40] who were immunocompromised or had a family member with a compromised immune system [46] were more likely to accept a COVID-19 vaccine. Individuals previously infected with COVID-19 [26] were hesitant, as were those who engaged in homoeopathy or naturopathy practices [46]. Students who exhibited general opposition to vaccines [46] and previous hesitancy towards other vaccinations [26] were also more likely to exhibit hesitancy towards a COVID-19 vaccine. Alternatively, students who had received an inoculation in the past five years [29, 39] or were willing to accept an influenza shot [46] were more likely to accept a COVID-19 inoculation. Individuals who perceived themselves at higher risk of a severe COVID-19 infection now and in the future were more likely to accept a COVID-19 inoculation [20, 29, 39].

Vaccine-related factors: Healthcare students that expressed more worries and concerns about the efficacy of the vaccine [20, 40], the safety of the vaccine [36, 40] and the adverse side effects from the vaccine [20, 26, 40, 45, 46] were more hesitant to accept the COVID-19 vaccine. Alternatively, healthcare students less concerned about adverse side effects [45] and who perceived the vaccine to be effective [39, 46] and beneficial [36] were more accepting of an inoculation. Additionally, a fee-based vaccine was associated with more hesitancy than a freely available vaccine [35].

Information and sources: Students who perceived a lack of information about the vaccine [20, 36, 40] and data on its side effects [20, 36] exhibited more hesitancy towards a COVID-19 vaccine. Individuals who perceived sufficient knowledge regarding COVID-19 [26, 29, 45] and realised the importance of COVID-19 [26] and an associated vaccine [45] were more likely to accept an inoculation. Evidence suggests that using social media for COVID-19 vaccine-related information was found to be both a barrier [26] and a facilitator [39] of vaccine acceptance. Furthermore, the use of scientists [45] or pharmaceutical companies [45] as a source of information about COVID-19 vaccines was associated with vaccine uptake. Contrastingly, exposure to conspiracy theories was associated with greater hesitancy [46].

Trust factors: Higher levels of vaccine acceptance were associated with higher levels of trust or confidence in the government [36, 46], mass media [45, 46], social media [45], healthcare systems and agencies [45, 46], public health experts [45], health promotion strategies [36], scientists [45] or pharmaceutical companies [45].

Social factors: Social factors associated with vaccine acceptance were the presence of COVID-19 infection within a close social network [29], having family members that had received a COVID-19 vaccine [40] and suffering from distance to friends during pandemic containment [26]. Additionally, students expressing fear of death rates were more accepting of a vaccine [26].

3.6.4 Results from meta-analyses.

Four reviews conducted a meta-analysis exploring the role sociodemographic variables have on determining COVID-19 vaccine hesitancy or acceptance in HCWs or healthcare students. For HCWs, the only variables found to significantly predict vaccine acceptance was being male [28, 29], aged 30 years or older [28], having a history of prior influenza vaccination [28] and perceived risk of COVID-19 infection [29] (S2 Table). Unlike HCWS, age [26] and gender [26, 31] were not significant predictors of vaccine acceptance for healthcare students. Factors related to vaccine uptake for this population were being a student in a medical field [26], supporting compulsory vaccination [26, 31], perceived risk of COVID-19 infection [26], perceived sufficient knowledge of COVID-19 [26] and recognition of the importance of COVID-19 vaccination for individuals [26]. Alternatively, healthcare students previously infected with COVID-19, those worried about the vaccine’s adverse effects, or those with negative attitudes toward compulsory vaccination [26] were significantly more hesitant to accept a COVID-19 vaccination (S3 Table).

4. Discussion

This is the first comprehensive Umbrella Review that has compiled the evidence pertaining to vaccine hesitancy and acceptance of a COVID-19 vaccine for HCWs and healthcare students. This review found that vaccine hesitancy rates were variable across occupational roles, whereby some professions, such as physicians [49] and dental practitioners [27], were more accepting of a COVID-19 vaccine than other occupations, for instance, nurses [41, 46, 48]. In several reviews where acceptance rates were compared to the general public, HCWs displayed more hesitancy toward the COVID-19 vaccine [28, 37, 29]. Most reviews exploring hesitancy in healthcare students found that medical students were less hesitant toward a COVID-19 vaccine than non-medical students [22, 35, 46]. Dental students exhibited more hesitancy than dental practitioners [27], and nursing students displayed higher acceptance rates than nurses [26]. The variability in hesitancy rates across various occupational groups suggests a need for tailored intervention strategies that address the barriers contributing to vaccine hesitancy for each occupational group. Previous research has found that educational sessions delivered by less hesitant HCWs effectively increased vaccine acceptance rates in previously hesitant HCWs [50, 51]. Implementing COVID-19-related information sessions across hospitals or departments that enable HCWs, such as nursing staff, to discuss concerns and questions with other HCWs (e.g. physicians) may be efficacious in improving COVID-19 vaccine uptake in more hesitant groups of HCWs. Similarly, educational interventions with healthcare students throughout their training courses may be a way to help address hesitancy and promote and maintain vaccine acceptance throughout their medical careers and beyond.

Many factors associated with vaccine hesitancy were identified, one of the most commonly explored and reported drivers was related to sociodemographic factors. Although there is an abundance of evidence pertaining to gender and age, the evidence is inconsistent. Regarding gender, being a male HCW was associated with vaccine acceptance [5, 22, 23, 25, 28–34, 36, 38–40, 42, 43, 46, 47], and was a significant predictor of COVID-19 vaccine uptake in two meta-analyses [28, 29]. However, being a female HCW was associated with both vaccine hesitancy [22, 23, 34, 36, 40, 43, 45] and vaccine acceptance [20, 23, 29, 34, 36, 48]. This pattern was also identified in healthcare students, whereby males were more accepting of an inoculation [20, 21, 29, 45, 46] and being female was both a barrier [31] and facilitator [39] of vaccination uptake. However, the results from two meta-analyses found that gender was not a significant predictor of vaccine acceptance for healthcare students [26, 31]. Regarding age, younger age (<40) and older age (>45) were both a barrier [20, 22, 25, 36, 45] and a facilitator [5, 20–23, 25, 28–30, 32–34, 36, 39, 42, 43, 45–48] of vaccine uptake in HCWs. One meta-analysis found that being 30 years or older was a significant predictor of vaccine acceptance in this population [28]. For healthcare students, older age was associated with acceptance [40, 45, 46]. However, a meta-analysis did not find age to predict vaccine uptake for healthcare students [26] significantly. For ethnicity, this review suggests that HCWs from White ethnic backgrounds [5, 23, 34, 40] were more accepting of a COVID-19 inoculation than those from Black [23, 30, 40, 42, 45] or Latin ethnic backgrounds [34, 45]. Being from an Asian ethnic background was a barrier [23, 45] and facilitator [23] of vaccine uptake in HCWs. Similarly, healthcare students from a Non-Hispanic White background were more accepting of a COVID-19 vaccine than healthcare students from a Black/African American background [40]. Other individual factors found to be associated with vaccine hesitancy for both HCWs and healthcare students were lower educational attainment [23, 31, 32, 36, 45, 48], lower income [20, 36, 48], or residing in low-and middle-income countries [27, 35]. In fact, literature highlighted that in some low and middle-income countries, the vaccine coverage is less than 20% and, in the general population, evidence suggests that people hesitant to COVID-19 vaccine belong to low socioeconomic groups, or to Asian and black ethnic groups, Muslims, and Buddhists [52, 53] It is possible that disinformation, in association with some religious beliefs, could discourage people to take the COVID-19 vaccine [53]. Also, studies carried out in Islamic regions, have shown that the willingness to purchase the covid-19 vaccine could be one of the influencing factors regarding the acceptance of the vaccine. A recent study [54], carried out in Indonesia, showed that only a small percentage of the population was willing to purchase a COVID-19, even if, the overall acceptance rate of a COVID-19 vaccine varied based on its effectiveness and the related risk of adverse effects. Further studies should explore more deeply and specifically the association of these variables with the level of vaccine hesitancy and acceptance of a COVID-19 vaccine for HCWs and healthcare students. To reduce hesitancy, vaccination programs and public health campaigns should tailor messages to reflect the variation in sociodemographic characteristics and the social and cultural norms surrounding the target group. The information and message delivered to the target group should be presented in a format that the target group can relate to and access.

Another driver of hesitancy in HCWs and healthcare students was related to concerns about the safety, efficacy and potential side-effects of a COVID-19 vaccine [5, 20, 36, 40, 48]. Moreover, the rapid development of the vaccine, perceived lack of clinical trials and an expedited approval and production process led to greater hesitancy in HCWs [33, 42, 48]. For healthcare students, financial barriers to the vaccine also increased hesitancy [35]. Confidence or trust in the safety and efficacy of a vaccine and the systems that develop, manufacture and distribute vaccines is an integral part of the decision-making process surrounding vaccine behaviours not just for HCWs and healthcare students but for the general population as well [21, 55]. Restoring confidence and trust in the COVID-19 vaccine can be achieved by increasing transparency and awareness of scientific rigour throughout the development, approval and distribution processes [56]. Tailored communication strategies that disseminate information regarding the progress of COVID-19 vaccines, as well as scientific data about the safety and efficacy of the vaccines to HCWs, may increase trust, help to expedite the decision-making process and lead to faster uptake of a COVID-19 inoculation in this sub-population [57].

This review also found that an individual’s previous vaccination behaviours were associated with current vaccination intentions [5, 25, 26, 30, 39, 48]. A meta-analysis found that previous history of influenza vaccine uptake was a significant determinant of vaccine acceptance in HCWs [28]. These findings highlight the importance of continuously promoting favourable behaviours and attitudes toward vaccination programmes throughout an individual’s healthcare career. Vaccine promotion campaigns continuously rolled out within healthcare institutions could also play a critical role in shaping future vaccination intentions and facilitate HCWs’ willingness to vaccinate without delay in response to future infectious disease outbreaks [58]. Another driver of vaccine intentions was a history of a COVID-19 infection. HCWs and healthcare students who had already contracted COVID-19 were more hesitant to accept vaccination [26, 34, 45, 47, 48]. More than likely due to the belief that natural immunity offers a level of protection against further infections, reducing the perceived need for an inoculation [59]. However, research has found that around a third of individuals do not develop natural immunity after recovering from a COVID-19 infection [60], and in those that do, natural immunity may wane quicker than vaccine-induced immunity [61]. Similarly, the risk of re-infection is increased [62] and the chances of long-term damage (long-COVID) also increase in unvaccinated individuals [63]. Educating HCWs and healthcare students about the increased risk of re-infection due to occupational exposure and the negative health impacts of repeated exposure may be an effective strategy to encourage uptake in previously hesitant HCWs.

Several drivers related to workplace settings were also found to affect vaccination behaviours. For example, being involved in COVID-19-related duties [29, 41, 48], being in regular contact with COVID-19 infected patients [25, 34, 39, 47], perceiving a lack of PPE and inadequacies in workplace infection control policies [46] were all factors found to increase uptake behaviours in HCWs. Meta-analyses found that perceived risk of COVID-19 infection was a significant determinant of vaccine intentions for HCWs and healthcare students [26, 29]. Specifically, individuals perceiving themselves as at higher risk of contracting a COVID-19 infection were more willing to accept a vaccine [26, 29]. Negative perceptions of risk may be due to a perceived lack of likelihood, susceptibility and severity of infection within the workplace [64]. Strategies to improve uptake in HCWs have focused on implementing mandatory vaccinations; however, this strategy may be counterproductive for some individuals. For example, this review found that HCWs and healthcare students who disagreed with compulsory vaccination were more hesitant than those supporting mandatory policies [26, 31, 33, 36]. A meta-analysis found disagreement with compulsory vaccination to be a significant predictor of hesitancy in healthcare students [26]. Mandatory vaccination policies may not be the most effective approach to reduce hesitancy in this population and implementing such enforcements could have additional consequences on staffing levels and care provisions in some already-stretched medical institutions [65]. Alternative strategies focused on building trust and addressing the concerns of hesitant HCWs and healthcare students may yield greater results.

Moreover, an individual’s social network was instrumental in promoting vaccine acceptance, and this may be a potential avenue to model intervention strategies. For example, HCWs that received encouragement or recommendations to vaccinate from their close social networks, colleagues, or other healthcare professionals were more willing to accept an inoculation [29, 33, 36, 48]. Moreover, HCWs who displayed higher levels of altruism [32, 45, 48] and perceived vaccination as a collective responsibility [22, 39, 48] were more likely to accept a COVID-19 vaccine. Previous research has found that influence and pressure from social networks can be instrumental in changing behaviour [66]. For example, when close social networks engage in preventative measures (e.g. social distancing, face-mask wearing) [67] and adherence to rules is a norm endorsed by the social network [68, 69], then individuals are more likely to follow and engage in the behaviours exhibited by the social group. Therefore, strategies encouraging vaccinated HCWs and family members of HCWs to advocate for adherence to vaccination recommendations may apply social pressure and, as a result, coax hesitant HCWs into accepting a COVID-19 inoculation. Moreover, occupational communication and incentives could focus on lauding vaccinated individuals for their altruistic and collectivistic values, which may motivate hesitant HCWs to receive COVID-19 vaccination to be perceived as contributing to society’s collective behaviours.

Perceptions of the availability and adequacy of COVID-19 information and data and the sources used to seek out COVID-19-related information were found to be drivers of vaccination intentions for HCWs and healthcare students. For example, individuals who perceived a lack of adequate scientific information about the vaccine and its side effects were more hesitant to accept a COVID-19 inoculation [20, 24, 36, 48], as were those whose primary source of COVID-19 information came from social media platforms [26, 30]. Alternatively, HCWs and healthcare students who utilised reliable sources for COVID-19-related information [36, 39, 45] and perceived the information to be adequate [20, 24, 36, 48] were more accepting of a COVID-19 vaccine. This finding would suggest that levels of health literacy, defined as “the degree to which individuals have the capacity to obtain, process and understand basic health information needed to make appropriate health decisions” [70, pg. 6], may be lower in some HCWs and healthcare students. Interventions aimed at improving health literacy and digital health literacy may be efficacious in increasing vaccine acceptance in this population. For example, equipping an individual with skills to enhance their information-seeking behaviours will improve perceptions and adequacy of information and inform decision-making processes, potentially leading to voluntary uptake. Another driver of hesitancy for HCWs and healthcare students was exposure to misinformation or conspiracy theories on social media [5, 22, 32, 46]. Although efforts have been made to manage the spread of COVID-19 misinformation on social media platforms (e.g. fact-checking, misinformation awareness campaigns) [71], more could be done at an individual and occupational level to reduce the impact misinformation has on the vaccination behaviour of HCWs and healthcare students. One potential strategy would be to utilise pre-bunking; this is where the impacts (changes in beliefs and behaviours) of misinformation are neutralised by pre-exposure to accurate information [72]. As such, strategies to regularly expose HCWs and healthcare students to scientific, accurate information about COVID-19 and the vaccines from trusted medical bodies within the workplace may reduce the influence misinformation may have on the vaccination intentions of HCWs and healthcare students. Moreover, media literacy resources, such as “Go Viral”, an interactive game supported by the WHO that teaches individuals to identify and resist being influenced by COVID-19 misinformation [73], could be recommended to HCWs and healthcare students which could also reduce the likelihood of hesitancy towards COVID-19 vaccines as a result of exposure to misinformation on social media platforms.

Furthermore, the level of trust HCWs and healthcare students held towards key social actors, such as the government, public health authorities, health experts, vaccine manufacturers, pharmaceutical companies and scientists, was pivotal in shaping vaccination intentions. Specifically, a lack of trust in these social actors was associated with hesitancy toward accepting a COVID-19 vaccine [5, 36, 42, 45, 46, 48]. Moreover, a lack of trust in pandemic management [20, 21, 34] and health promotion strategies [36], as well as exposure to conflicting or unclear COVID-19 information by the government or public health figures [30, 48], lead to greater hesitancy for HCWs. Strategies that improve and build trust towards the government, health authorities and other influential social actors are imperative to ensure that vaccine uptake remains high in populations of HCWs and healthcare students. To enhance trust in COVID-19 vaccination, governments should strive to be transparent about vaccination strategies and maintain integrity and accountability throughout vaccine development, approval, distribution and administration. Information regarding these stages must be released in a timely, accurate and accessible manner to the general public and healthcare professionals. Moreover, health communication messages and campaigns delivered by the government or health officials must strive to be coherent, authoritative and free of ambiguity or conflicting information. These strategies would contribute to an individual’s decision-making process and foster trust and confidence in key social actors, ultimately leading to greater uptake of COVID-19 vaccinations in HCWs, healthcare students, and the general population [74].

In summary, this review has synthesised the most commonly reported factors associated with COVID-19 vaccine acceptance and hesitancy for HCWs and healthcare students. Frequent reasons associated with vaccination intentions were related to sociodemographic factors, COVID-19 exposure, perceived risk, attitudes towards mandatory vaccination, vaccination history, perceptions regarding the safety, efficacy and side-effects of the COVID-19 vaccine, perceptions about the rapid development, testing, approval and distribution of the vaccine, social pressure, altruism, collective responsibility, trust of key social actors, perceptions of pandemic management, perceived adequacy of information, usage of social media and exposure to misinformation. Although identifying these factors may provide potential areas for intervention, there are several points to consider. Firstly, most of the reviews included in this synthesis investigated prospective attitudes and behavioural intentions toward a COVID-19 vaccine, which does not always translate to actual behaviour [75, 76]. For example, research exploring the relationship between HCWs intentions and future acceptance of an influenza vaccine found that 42% of HCWs who intended to accept the vaccine failed to act on those intentions [77]. Future research exploring the factors that lead to changes in intentions is needed as these drivers may be pivotal to developing effective intervention strategies. Moreover, the evidence in this review only considers a single inoculation; however, some COVID-19 vaccines require multiple doses and booster shots. Hesitancy towards additional inoculations may hamper current vaccination progress and contribute to the circulation of the virus and the development and spread of new variants [78]. Therefore, future research should explore acceptance intentions towards multiple inoculations.

5. Conclusion

Individual decision-making regarding vaccination is a complex process, driven by a mix of scientific, social, behavioural, cultural, emotional, environmental and psychological factors. HCWs and healthcare students are key populations to consider when planning vaccination campaigns. The determinants of vaccination hesitancy among HCWs are mainly related to concerns about the vaccine’s side effects or lack of scientific information about the vaccine itself along with being affected by chronic conditions or not. Among healthcare students, non-medical students showed higher hesitancy, while students living with relatives in vulnerable conditions are less hesitant. In both populations, the lack of scientific information or the social media usage is related to vaccination hesitancy.

Strategies to reduce COVID-19 vaccine hesitancy in this population require a multifaceted approach targeting amenable drivers at the individual, occupational and societal level. At the individual level, educational interventions aimed at improving health literacy, knowledge of COVID-19 and associated vaccines, reducing susceptibility to misinformation and promoting pro-vaccination behaviours during medical training might increase COVID-19 vaccination uptake in both HCWs and healthcare students. At the occupational level, strategies to minimise vaccine hesitancy in this population may consist of distributing and ensuring access to accurate scientific information, promoting and rewarding pro-vaccination behaviours, implementing mandatory training sessions to improve health literacy, recommending engagement with media literacy resources, as well as facilitating regular interactive sessions lead by pro-vaccination HCWs to educate and address the vaccine-related concerns held by hesitant HCWs and healthcare students. At the societal level, hesitancy could be addressed through the delivery of sociodemographic-specific vaccination programs and public health campaigns, the dissemination of scientific information regarding COVID-19 vaccine progress reports to medical institutions and staff, through transparent and accurate communication messages from government and other trusted social actors, avoidance of unclear or conflicting messages to HCWs, as well as social pressure from other HCWs and broader social networks. There is evidence to suggest that these interventions may be effective at improving COVID-19 vaccine uptake; however, further research is needed to assess the efficacy of these strategies with HCWs and healthcare students.

Supporting information

Acknowledgments

Authors acknowledge Dr Giancarlo Cicolini (University of Bari) for his support and advice.