Dengue is no longer a rare disease because dengue cases have been on the rise globally including in Malaysia. The disease poses a threat to health and the economy in tropical and subtropical countries [1]. The main vectors responsible for the dengue disease are Aedes aegypti and Aedes albopictus. Besides, these mosquitoes are also responsible for chikungunya and Zika viruses [2]. Several serotypes of dengue diseases are DENV 1, DENV 2, DENV 3, and DENV 4. There are many current approaches to combat dengue, such as fogging, indoor and outdoor residual spraying, the release of the male Wolbachia-infected Aedes mosquitoes, the development of genetically modified Aedes mosquitoes, and others. These approaches were the current technology in use, and some are currently in research to reduce all dengue virus serotypes in Malaysia. However, the dengue vaccine development is a promising approach to protect the community from dengue.
After decades of research by Sanofi Pasteur, the first dengue vaccine, Dengvaxia® (CYD-TDV), was first licensed in Mexico in December 2015 for individuals between 9–45 years old, living in endemic areas. The vaccine is now available in 20 countries [3] and has been used in large-scale vaccination programmes in the Philippines, engaging over 800,000 school children [4]. Dengvaxia® has the potential to reduce the dengue burden in endemic populations due to its cost-effectiveness, efficacy, and user-friendly feature [5]. According to Pasteur's research, the vaccine is more effective and is encouraged to be injected into people who have been infected with the disease [6].
Flasche et al. [7] showed that dengue vaccine implementation would reduce dengue symptoms and hospitalisation rate by 13% to 25% in the first 30 years after vaccination. Although Shim [8] indicated that age-targeted Dengvaxia® vaccination is cost-effective in Brazil, the results indicated that routine vaccination of 70% of nine-year-olds reduces the dengue infection by 79% and if the targeted age group widens, the cost-effectiveness is reduced. Espana et al. [9] also discovered that the vaccine could reduce severe dengue by preventing 5.5% of hospitalisations. Besides, their findings also revealed that this intervention could be cost-effective in Puerto Rico at the cost of 382 USD. Moreover, herd immunity from Dengvaxia® promises a sense of security and safety from dengue disease [9]. Dengvaxia® has 66% efficacy, which could benefit public health and economics because the protection level is considerable [10]. However, there is still a need for more research on a dengue vaccine that will be effective for all age groups.
Despite the vaccine’s potential, Malaysia has conditionally approved the vaccine for testing despite the vaccine's potential, but it has not been fully implemented. So, it is important to study the public acceptance of this new approach before its adoption. In Malaysia, Yeo and Shafie [1] researched the public’s acceptance of the dengue vaccine to determine their willingness to pay for the vaccine, the respondents from Pulau Pinang positively reacted to the dengue vaccine and indicated their willingness to pay for the vaccine for the sake of their health. In another research, Arifah et al. [11] showed that health workers in Klang Valley were willing to pay between RM1 to RM500 (0–120 USD) for the dengue vaccine. Thus, their willingness to pay for the vaccine shows their acceptance of the vaccine.
Therefore, this study supports the studies mentioned above and a follow-up from the study of Arham et al. [12, 13], who examined stakeholders' acceptance of Outdoor Residual Spraying and Wolbachia-infected Aedes mosquitoes' techniques, which indicated that they positively support the approaches. Hence, a study focusing on the stakeholders' acceptance of the dengue vaccine and its predictors is also needed. Therefore, the main objective of this study is to determine the Malaysian stakeholders' acceptance of the dengue vaccine and determine its predicting factors. The finding will contribute to the existing literature on consumer behaviour toward adopting dengue vaccines. While also provides valuable information to the government, policymakers, and public health officials about effective strategies for driving dengue vaccine acceptance in Malaysia and other countries with a history of severe dengue transmission.
Theory and research hypotheses
The model theory of this study was developed and adapted based on the study by Amin and Hashim [14] which was developed from Fishbein’s attitude model. Amin and Hashim’s model became the main reference in determining the predictor factors influencing attitudes towards genetically modified mosquitoes as one of the dengue control techniques [14]. Therefore, four components proposed in the research model of this study include general factors, specific factors, attitude, and intention. General factors are predictive factors consisting trust in key players, attitudes to technology and religiosity. Previous studies tested all these factors as general factors in determining stakeholders’ acceptance of dengue controlling techniques [12,13,14,15,16,17]. These general factors have been observed to play a crucial role in directly and indirectly determining a person’s attitude and intention. Nevertheless, these general factors have been initially pioneered through past studies for trust in key players [18,19,20,21,22,23,24,25], attitudes to technology [21, 26,27,28], and religiosity [26, 27].
Specific factors, namely perceived benefit and perceived risk are predictive factors. Both of these factors have made clear direct contributions to determine attitude and intention towards dengue controlling techniques in past studies [12,13,14,15,16,17]. These two factors play significant roles by being an essential basis directly related to the formation of attitude and intention in past studies. These factors are commonly known to have an inverse relationship in determining attitude and intention [28,29,30,31,32,33,34]. Attitude and intention are components that determine the views, acceptance, or approval to express support for something. Attitude represents beliefs that describe actions to behave based on positive or negative intention [35,36,37].
The hypotheses were developed based on the Pearson correlation method [38]. Therefore, 15 hypotheses were developed according to the study’s framework to determine the relationship of predictor factors with the attitude and intention of stakeholders’ acceptance of the dengue vaccine (Refer to Fig. 1).
H1: Attitudes has a significant influence on intention among stakeholder to adopt the dengue vaccine
H2: Perceived benefit has a significant influence on intention among stakeholders to adopt the dengue vaccine
H3: Perceived risk has a significant influence on intention among stakeholders to adopt the dengue vaccine
H4: Perceived benefit has a significant influence on attitude among stakeholders to adopt the dengue vaccine
H5: Perceived risk has a significant influence on attitude among stakeholders to adopt the dengue vaccine
H6: Trust in key players has a significant influence on attitude among stakeholders to adopt the dengue vaccine
H7: Attitude to technology has a significant influence on attitude among stakeholders to adopt the dengue vaccine
H8: Religiosity has a significant influence on attitude among stakeholders to adopt the dengue vaccine
H9: Trust in key players has a significant influence on perceived benefit among stakeholders to adopt the dengue vaccine
H10: Attitude to technology has a significant influence on perceived benefit among stakeholders to adopt the dengue vaccine
H11: Religiosity has a significant influence on perceived benefit among stakeholders to adopt the dengue vaccine
H12: Trust in key players has a significant influence on perceived risk among stakeholders to adopt the dengue vaccine
H13: Attitude to technology has a significant influence on perceived risk among stakeholders to adopt the dengue vaccine
H14: Religiosity has a significant influence on perceived risk among stakeholders to adopt the dengue vaccine
H15: Perceived benefit has a significant influence on perceived risk among stakeholders to adopt the dengue vaccine
Methodology
Study design, location, and duration
A close-ended multidimensional survey instrument was designed to identify factors influencing stakeholders’ acceptance of the dengue vaccine in Klang Valley, Malaysia. The instruments used in this study consist of seven variables: 1) trust in key players, 2) attitudes to technology, 3) religiosity, 4) perceived benefit, 5) perceived risk, 6) attitude and 7) intention to dengue vaccine. The items used were adapted and modified from previously published work by Amin and Hashim [14] and previous studies [18,19,20,21,22,23,24,25,26,27]. Klang Valley was chosen as the location of the study because this area is the hotspot of dengue cases in Malaysia (http://idengue.arsm.gov.my) and the center of socio-economic development.
The questionnaire was developed in Malay and translated into English to allow respondents to choose to respond in a language that they were more comfortable. Certified translators validated the two-way translation. Respondents were asked to evaluate their opinion on a 7-point Likert scale ranging from 1 (strongly disagree) to 7 (strongly agree) for each item in this instrument. According to Churchill and Dawn [39], Likert-scale questionnaires need to have many options so that the respondents can give the closest answer and represent themselves. Likewise, Wu and Leung [40] also reported that an increased number of Likert-type scale points will result in a closer approach to the underlying distribution, hence normality and interval scales.
Experts in environmental health, social science, and governance examined the content and face validity of the questionnaires. Prior to the actual study, 126 questionnaires were distributed for a pilot study to test the strength of the items used and determine the research instruments' validity and reliability. After the pilot study, an exploratory principal component factor analysis followed by varimax rotation was carried out to identify items best expressive of attitudinal dimensions. The items which cross-loaded on more than two factors and were difficult to interpret, with factor loadings lower than 0.50 or inconsistency, were deleted. The enumerators continue to distribute the questionnaire from September 2016 to September 2017.
Ethics statement
Before the study's procedures, participants consented verbally and voluntarily, and all was done following the Declaration of Helsinki and the Malaysian Ministry of Health's Medical Review & Ethics Committee (MREC). Therefore, ethical approval was not required for this study since under the Guidelines for Ethical Review of Clinical Research or Research involving human subjects, Medical Review and Ethics Committee [2006] (www.nccr.gov.my/index.cfm?menuid=26&parentid=17), research involving questionnaires with no collection of identifiable private information is exempted from review by the Medical Review and Ethics Committee.
Sample size, participation, and data collection
Faul et al. [41] suggested conducting statistical analysis for social and behavioural sciences using the G*Power 3.1.9.2 software. This software used a linear multiple regression test to determine the sample size using statistical power of 0.80 [42], medium-size effect (f = 0.15), and significance level (p = 0.05) with 15 paths of exogenous latent variables representing 15 hypotheses predicted to have an impact in the research conceptual framework model. The analysis indicated that this study only required 139 respondents. Therefore, this study also considers the total population located in the Klang Valley and the number of dengue cases in 2015, which recorded 23,355 dengue cases reported by OR Technologies, Malaysia (https://public.tableau.com/app/profile/ortechnologies/viz/KadarKesKematianAkibatDenggi2010-2015hackathon2/KadarKesKematianAkibatDenggi2010-2015).
Using stratified random sampling, this survey was undertaken face-to-face among 415 Malaysian adults (aged 18 years and above). However, only 399 respondents were analysed after validity and reliability screening due to complete responses and no biased. Krejcie and Morgan [43] proposed a total sample size of 384 respondents for over 1 million population. Hence, the total sample of respondents for scientists and the public in this study is considered sufficient. The respondents were initially divided into two groups: scientists (n = 202) and the general public (n = 197). The two groups were merged for analysis as they share a common interest in adopting the dengue vaccine. Academicians, postgraduate students, research officers working in environmental science, biological sciences, health, and genetic sciences research, and those participating in dengue control and prevention are categorised as scientists. The public consists of people living in outbreak regions in the Klang Valley, classified as areas with high Aedes mosquito numbers. The participation of the respondents was voluntary. Nevertheless, informed consent was obtained verbally, and the respondents’ details were kept confidential.
Data analysis
Partial Least Square Structural Equation Modelling (PLS-SEM) using the Smart Partial Least Square (Smart-PLS) software version 3.3.9 was employed to assess the hypothesised relationships [44]. This approach is particularly beneficial in justifying the interaction between multiple factors to explain complicated behaviour [45]. Firstly, the measurement model was investigated to determine the validity and reliability. Subsequently, the structural model was tested to test the hypotheses, including the model fit test [46, 47]. In addition, a bootstrapping approach with 5000 resamples was utilised to determine the relevance of the path coefficient and loading. A normality test for statistical analysis was also performed to confirm that the data did not cut off the normality criterion [45, 46, 48,49,50].