Introduction
Annual vaccinations have emerged as the most significant interventions to reduce the clinical and economic impact of COVID-19 and influenza, particularly among high-risk populations such as the elderly and individuals with comorbidities (de Fougerolles et al., 2024; Su et al., 2021; Utami et al., 2023). The European Center for Disease Control and Prevention has emphasised the importance of timely and adequate COVID-19 and influenza vaccination coverage, especially among risk groups, ahead of the winter season when infection rates reach their peak (ECDC, 2024; Liu et al., 2021; Nypaver et al., 2021). Notably, the co-administration of COVID-19 and influenza vaccines has emerged over the past few years as a critical strategy to enhance vaccination coverage (Achterbergh et al., 2024). Nevertheless, both COVID-19 and influenza vaccination rates are suboptimal across several European countries (Chen et al., 2022; Lazarus et al., 2023; Mathieu et al., 2020). For example, influenza vaccination rates among the general population range from 12% in Hungary to 52% in Greece (Chen et al., 2022). With regards to COVID-19 vaccines, 70% of the population in Europe has received at least one dose of the COVID-19 vaccine (Our World in Data, 2024a) and 67% have completed the initial vaccine protocol up to August 2024 (Our World in Data, 2024b). Despite vaccines availability, vaccination is sometimes compromised by vaccine hesitancy (Salmon et al., 2015), defined as the delay in acceptance or refusal of vaccines (MacDonald, 2015).
Healthcare professionals (HCPs) play a pivotal role in their patients’ decision to get vaccinated (Griffin et al., 2018; Karafillakis et al., 2016). During the COVID-19 pandemic, recommendations by HCPs were among the strongest predictors of vaccination uptake (Karlsson et al., 2021; Meissner, 2022). Being among the most trusted advisors in vaccination decision-making, HCPs should be at the forefront of efforts to enhance vaccine uptake (Paterson et al., 2016). However, encouraging HCPs to provide recommendations and actively promote vaccination remains a significant challenge. In the post-COVID-19 era, understanding HCPs readiness to promote annual vaccines, including COVID-19 and influenza vaccines, and, indeed, defining it in behaviour terms, is essential to inform targeted intervention and policy strategies.
Insights from behavioural theories are useful to better understand the barriers and facilitators of promoting vaccination by HCPs. The Capabilities, Opportunities, Motivation-Behaviour (COM-B) theoretical model was developed to understand the determinants of any health behaviour, based on 19 frameworks of behaviour change (Michie et al., 2011). It has been adapted by the World Health Organisation (WHO) for their Tailoring Immunization Programmes (TIP) approach (Habersaat & Jackson, 2020). The COM-B model asserts that for any health behaviour to occur, 'Capability', 'Opportunity', and 'Motivation' need to be present (Michie et al., 2011). It offers a comprehensive theoretical framework to identify both individual and contextual barriers and facilitators of vaccination promotion by HCPs. Capability taps on individual-level determinants (such as lack of information, distrust or misperceptions), opportunity is largely influenced by context or interaction of the person with others (including social, cultural, institutional, and political factors) and motivation contains elements of both individual level (beliefs and perceptions) and context determinants (rewards, recognition, professional roles and responsibilities). These determinants can then be mapped to evidence-based intervention functions and subsequent policy domains.
Current evidence related to the determinants of vaccination promotion or delivery by HCPs confirms that factors in all three domains of the COM-B model are relevant (Bolsewicz et al., 2022; Flood et al., 2023; Musa et al., 2020; Nnaji et al., 2023; Norman et al., 2022; Overmars et al., 2022; Randall et al., 2021; Thomas et al., 2018; Thomas et al., 2019; Tuckerman et al., 2020; Zaouk et al., 2020; Zhou et al., 2023). For example, previous studies on influenza vaccination have highlighted the role of inconsistent vaccine supply (Randall et al., 2021), time pressure (Randall et al., 2021), lack of educational resources (Randall et al., 2021), ineffective communication with patients (Tuckerman et al., 2020), knowledge of vaccine recommendations (Tuckerman et al., 2020), and perceived responsibility towards recommending or delivering the vaccine (Norman et al., 2022; Tuckerman et al., 2020). Previous evidence, however, derives solely from qualitative studies. None of previous quantitative measures have been designed to measure HCPs’ readiness to promote vaccination based on the COM-B model. The newly-developed questionnaire will be used in various clinical settings and in different countries to provide quick, measurable, and comparable outcomes as well as metrics of performance to support the development of targeted vaccination promotion strategies and policymaking decisions.
The proposed study is part of a larger, ongoing project entitled ‘Developing a Country-Observatory for Sharing Best Practices for Vaccination Promotion (co-OPERATOR), funded by the European Health and Digital Executive Agency (EU4Health scheme). The overarching aim of the co-OPERATOR project is to develop an innovative and citizen-centered digital solution with an evidence-based virtual observatory to increase vaccine literacy and uptake among participating countries (Cyprus, Greece, Italy, Portugal) and beyond. One of the primary objectives of the co-OPERATOR project is to assist decision-makers in understanding the barriers and facilitators influencing COVID-19 and influenza vaccination promotion by HCPs and to translate scientific evidence into effective intervention strategies at regional, national, and European level. These cross-country efforts are important as certain factors may exhibit specificity to particular countries, reflecting the different challenges faced within diverse socio-cultural and system-level local and regional contexts.
Study objectives
The objectives of the proposed study are a) to develop a questionnaire informed by the COM-B theoretical model taping on the readiness of HCPs to promote COVID-19 and influenza vaccination, b) to translate and culturally adapt the questionnaire to be administered in Cyprus, Greece, Italy, and Portugal, and c) to examine the validity (content, discriminant, factorial, predictive, cross-cultural), reliability (internal consistency, test-retest), and acceptability of the Greek, Italian, and Portuguese versions of the scale.
Protocol
Methods
Study design
The COM-B Readiness to Promote Vaccination Questionnaire will be developed in three phases (Boateng et al., 2018): Item development (which has been completed), questionnaire development (in progress), and questionnaire evaluation (pending). This study adheres to the ethical principles outlined in the Declaration of Helsinki (latest version, 2024), which governs research involving human participants. Ethical approval was obtained from Cyprus National Bioethics Committee (reference number: ΕΕΒΚ ΕΠ 2024 01 238, date of approval: 21/08/2024) for Cyprus (Cyprus University of Technology) and Greece (University of Crete), the University of Pisa Bioethics Committee (reference number: 56/2024, date of approval: 8/10/2024), and the Ethics Council of the Lisbon Nursing School (reference number: 5380/2024, date of approval: 23/10/2024). The item development phase initiated in February 2024, but research activities involving participants in each country take place after obtaining ethical approval.
Phase 1: Item development
Deductive methods have been applied by the lead author (LP) through literature review and assessment of existing scales and items tapping on the COM-B model domains. Only two questionnaires based on the COM-B model were identified, measuring factors associated with Human Papilloma Virus and dengue vaccination in the population, respectively (Cordoba-Sanchez et al., 2022; Shafie et al., 2023). A 6-item COM-B questionnaire has also been developed to assess perceived capabilities, opportunities, and motivation in HCPs (Keyworth et al., 2020). This brief, generic measure targets any health behaviour rather than vaccination or vaccination promotion specifically. Quantitative measures informed by the COM-B model have been developed, although these primarily target other HCPs’ behaviors. Examples include delivering physical activity advice to cancer patients (Webb et al., 2016), implementing falls prevention programs in acute hospitals (Ayton et al., 2017), applying health interventions after cardiac surgery (Jordens et al., 2024), and adopting hand hygiene practices (Zheng et al., 2022). A more relevant instrument, the Pro-VC-Be (Health Professionals Vaccine Confidence and Behaviors) questionnaire, has been developed to measure psychosocial determinants of HCPs' vaccination behaviors (own vaccine uptake and recommendations) but it is not structured around the COM-B model (Verger et al., 2022). Concluding, none of these scales have been specifically designed to measure HCPs’ readiness to promote vaccination based on the COM-B, hence do not adequately serve the purpose of this work.
In contrast, the TIP guide (WHO, 2019) has been identified as a useful and comprehensive tool for the purposes of this study. Specifically, the TIP approach, which is grounded on the COM-B model, has been developed by the WHO Regional Office for Europe to help countries achieve increased and equitable vaccination uptake through integrating research and behavioural insights into immunisation program planning and policy in each country (WHO, 2019). While the guide does not provide specific questionnaire items, it includes a long list of relevant topics for exploring HCPs’ experiences, mapped onto the COM-B model. Thus, it provided a useful basis to inform and guide the item development phase of the questionnaire. One hundred and two items were initially developed, including both close-ended (45 items with on a 5-point Likert-type response scale ranging from 1 = not at all/completely disagree to 5 = to a great extent/completely agree) as well as open-ended (6 items) questions. Several items were included twice in order to refer to COVID-19 and influenza vaccines separately. In the first instance, the items were developed in the English language to allow input from international experts.
Content validity was assessed through an Expert Consensus Study carried out in October 2024 to evaluate whether the items adequately measure the COM-B domains. The group of experts consisted of five members, selected accordingly to combine expertise on the COM-B model, questionnaire development, and/or vaccination policy. Experts were asked to review the questionnaire items and rate the degree to which they agree or disagree with the inclusion of each item using a scale from 1 = strongly disagree to 5 = strongly agree. The experts could suggest re-wording of the items and/or response options as well as propose additional items to include. They were also asked to provide free comments regarding the relevance of each item and the representation of the domain of interest. During an online meeting, experts elaborated on their written feedback and disagreements were resolved in order to come to a consensus on the items included, excluded, and modified based on majority opinion. Experts’ ratings will be analysed to provide inter-rater reliability, while qualitative feedback (written and verbal) will be summarised thematically and discussed internally within the research team in order to revise the questionnaire accordingly.
Phase 2: Questionnaire development
The previous phase will result in a revised version of the questionnaire, which will be translated and culturally adapted in Greek, Italian and Portuguese. A standard procedure will be adopted in all countries; forward and backward translations will be conducted by two independent translators at each stage, fluent in English and the local language, one who is familiar with the topic (i.e. member of each local research team) and one lay translator. Linguistic and semantic equivalence approach will be followed to allow for the closest direct counterparts in structure, grammar, and vocabulary between the target languages. Expert reviewing of translation will then follow; Local experts (N=4–7) who are fluent in both English and the local language and have an expertise on the topic, will be invited to provide written feedback on the suitability of the translated questionnaire including whether it is well-adapted to the local language, preserving the meaning and intention of the original item, and in keeping with the socio-cultural context and healthcare system. Experts’ written feedback will be addressed by each local team in order to revise each translated version of the questionnaire accordingly.
Cognitive interviews with end-users will follow (N=5–15 per country) to assess the readability, understandability, and usability of the questionnaire, as well as the appropriateness of the response options. More precisely, participants will be asked to complete the questionnaire and provide their ratings on whether the questions are a) clear, b) easy to understand, c) well-adapted to the local language, d) socio-cultural context, and e) healthcare system, as well as on f) the appropriateness of the response options. Respondents will be asked to verbalise the mental process entailed in completing the questionnaire and to provide written and verbal comments and suggestions, both for specific items as well as for the overall questionnaire. Cognitive interviews will take place either online or in-person. Respondents’ ratings will be analysed descriptively and qualitative feedback (written and verbal) will be summarised in a consistent way to facilitate comparisons and discussions between the research teams in the different countries to identify ways to address feedback. General comments (e.g., questionnaire’s length) will be resolved by the research team by amending the original English version of the questionnaire whereas specific comments which apply only to a certain country will be resolved locally (e.g., adapting and fine-tuning a question to the local language/cultural context/healthcare system).
Inclusion criteria for cognitive interviews
The same eligibility criteria as in the main survey will be applied for the cognitive interviews. These are described below.
Phase 3: Questionnaire evaluation
Once the questionnaire development phase is completed, a larger sample of HCPs will be recruited cross-sectionally in each country to complete an online survey. Before progressing to the main recruitment, a purpose sample of HCPs (10% of final sample), stratified by occupational group as per inclusion criteria, will be invited to complete the online survey twice, with a 2-week in-between. Codes will be issued to preserve anonymity, and both the two measurements will be carried out online.
Inclusion criteria for cross-sectional survey
HCPs in the primary and secondary healthcare setting, medical doctors under specialisation training, nursing professionals, health visitors, pharmacists, medical/nursing/pharmacy trainees who a) reside and b) practice in the country in which the questionnaire will be administered, and c) who have a duty to promote COVID-19 and influenza vaccinations to the people they see in practice as part of their job role will be eligible to take part to the study. Information on the occupational group, country, and vaccination promotion duty will be provided by self-report.
Sampling and sample size calculation
The sample size for this validation study was calculated using precision analysis for the estimates of interest (e.g., percentage of participants reporting agreement with a particular questionnaire item). With no prior knowledge, the prevalence was set to 50%, for which a larger sample size will be required. The margin of error was set at 5% for the 95% confidence interval. Based on these parameters, we determined the total sample size of respondents necessary to achieve the required statistical precision (N = 376 participants per country).
Convenience sampling will be used to recruit participants from all occupational groups through the professional networks of the research team in each country as well as by invitation via professional associations’ emailing lists. REDCap software (projectredcap.org/software/) will be used for data collection across all sites. Occupational group will be monitored and efforts will be made to promote the survey in under-represented groups in order to maximize the heterogeneity of participant profile in the overall sample.
Study variables
Apart from the newly developed COM-B Readiness to Promote Vaccination Questionnaire, HCPs will also provide information on sociodemographic characteristics and place of work, own vaccination behaviour and intention, and their behaviour towards COVID-19 and influenza vaccination promotion as described below.
Sociodemographic characteristics
We will collect information on age, gender (man, woman, non-binary, other), and number and age of children.
Place of work
Participants will be asked to provide their place(s) of work (private office/clinic, public hospital/health centre, nursing home, pharmacy, Ministry of Health/Public Health Authority, University/Education sector, other.
Own vaccination behaviour and intention
We will obtain information on latest influenza vaccination (during last season, some time in the past, never), latest COVID-19 vaccination (within the last 6 months, within the last 12 months, some time in the past, never), and intention for annual vaccination with separate reference for COVID-19 and influenza vaccines (with responses ranging from 1 = I definitely would not to 5 = I definitely would).
Vaccination promotion behaviour
Questions relating to vaccination promotion practices will also be included, with separate reference for COVID-19 and influenza vaccines. More precisely, HCPs will be asked whether they actively promote COVID-19/influenza vaccination to the people they see in practice (no, yes to high-risk adults, yes to all adults) and whether they intend to actively promote annual COVID-19/influenza vaccination in the future to the people they see in practice (no, yes to high-risk adults, yes to all adults).
Data analysis
A common statistical analysis plan will be employed across sites to a) describe the distribution of responses to the questionnaire items and explore differences and associations with socio-demographic and other participant characteristics and b) evaluate the questionnaire’s metric properties. Statistical analyses will be carried out for the overall sample and separately for each country and for each vaccine type. For continuous variables, descriptive statistics will be summarised as means and standard deviations for variables which follow the normal distribution and medians and interquartile range for variables which do not follow the normal distribution. For categorical variables, descriptive statistics will be summarised as absolute (n) and relative (%) frequencies. Appropriate statistical tests and models will be used to examine any associations between the study variables (set for significance at 0.05). Statistical analyses will be carried out in STATA 18.0 (Stata Corp, College Station, TX, USA) and R programming language. To deal with missing data, full information maximum likelihood (Enders & Bandalos, 2001) and multiple imputation (Gottschall et al., 2012; Kenward & Carpenter, 2007) have been proven useful for questionnaire development, and will be considered in analyses.
Content validity will be examined using floor and ceiling effects calculated for each of the items. Discriminant validity will be tested with inter-item Pearson’s correlations which will be carried out to examine the extent to which scores on one item are related to scores on all other items of the same domain and to test the correlations between item scores and the sum domain score of the rest of the items excluding itself. Given the established COM-B framework guiding the development of the scale, the domains of the questionnaire were determined a priori: capabilities, opportunities, and motivation. Thus, a theoretical 3-factor model tapping on domains measuring capabilities, opportunities, and motivation will be explored. To explore the dimensionality and structure across the items of the questionnaire, exploratory factor analysis will be used. Items which cross-load will be examined and items with inadequate factor loadings or slope coefficients will be eliminated at this stage. Reliability testing will be used to explore the internal consistency of each identified factor using Cronbach’s alpha coefficient. To explore the factor structure further and verify the fit of a 3-factor model, a confirmatory 3-factor model consisting of domains measuring capabilities, opportunities, and motivation will be applied.
Test-retest consistency between two independent measurements will also be investigated with a 2-week interval time. The intraclass correlation coefficient and measurement error will be calculated, and Bland-Altman plots will be used to examine any systematic differences between test and retest scores. Predictive validity will be carried out using multivariable binary regression analyses to examine the degree to which the questionnaire score(s) are associated with vaccination promotion behaviour. Cross-cultural validity testing is only applicable with the Greek version of the scale, where comparisons will be made between the Cypriot and Greek sample using a multi-group confirmatory factor analysis. Criterion (concurrent) validity testing will not be performed as there is currently no gold standard measurement available to facilitate comparisons.
Finally, users’ acceptability will be investigated using missing data analyses, close-ended questions to assess perceived ease of understanding, interest, balance and fairness of the questionnaire, and a content analysis of open-ended comment boxes.
Conclusions
Expected outcomes
The expected outcomes of the proposed study are a) to develop a COM-B Readiness to Promote Vaccination Questionnaire on the readiness of HCPs to promote COVID-19 and influenza vaccination informed by the COM-B theoretical model, b) to translate and culturally adapt the questionnaire to be administered to HCPs in Cyprus, Greece, Italy, and Portugal, and c) to evaluate the validity (content, discriminant, structural, predictive, cross-sectional), reliability (internal consistency, test-retest), and acceptability of the Greek, Italian, and Portuguese versions of the questionnaire.
Impact
A novel questionnaire measuring the readiness of HCPs to promote COVID-19 and influenza vaccination will be developed, translated, culturally adapted, and validated in four European countries. Should the questionnaire be confirmed as psychometrically sound, it will be used in various clinical settings and in different countries to support decision-makers understand the determinants of promoting COVID-19 and influenza vaccination by HCPs hence develop effective vaccination strategies and campaigns focusing on the specific concerns and needs in order to tackle barriers and facilitate vaccine recommendation.
Risks
We anticipate no risks to study participants derived from their participation to the proposed survey.
Dissemination
Results from this study will be disseminated to the scientific community and the general public through Open Science Framework (osf.io) and open-access peer-reviewed publications.
Open science framework
The co-OPERATOR project is registered to the Open Science Framework:
https://osf.io/9fcdu/
DOI10.17605/OSF.IO/9FCDU
Ethics and consent
This study adheres to the ethical principles outlined in the Declaration of Helsinki (latest version, 2024), which governs research involving human participants. Ethical approval was obtained from Cyprus National Bioethics Committee (reference number: ΕΕΒΚ ΕΠ 2024 01 238, date of approval: 21/08/2024) for Cyprus (Cyprus University of Technology) and Greece (University of Crete), the University of Pisa Bioethics Committee (reference number: 56/2024, date of approval: 8/10/2024), and the Ethics Council of the Lisbon Nursing School (reference number: 5380/2024, date of approval: 9/9/2024).
Informed consent and privacy notification
Every participant will be provided with an information sheet online and an explicit consent form that explains the purpose of data collection, storage, and processing in compliance with European General Data Protection Regulation. Before proceeding with the completion of the online survey, all participants will be requested to provide their informed written consent to take part.
