The HBM is a well-established theoretical framework grounded in cognitive psychology, employed to examine health-related decision-making and health behavior adoption. The model posits that individuals' health behaviors are shaped by their perceived susceptibility and severity of a health threat, as well as by their assessment of the benefits and barriers of preventive actions (20). Additionally, the HBM incorporates cues to action that prompt behavioral responses and self-efficacy, which indicates an individual's confidence in their ability to carry out the desired behavior. The HBM is recognized as a dominant framework for health behavior research (21). Empirical studies have extensively applied the HBM across various health domains, providing a solid foundation for health intervention design, including breast cancer screening (22, 23), weight management (24), self-care practices (25), cervical cancer screening (26), oral health behaviors (27), and vaccination adherence (28). However, evidence indicates that HBM's predictive power is relatively weak (29). It suggests that theoretical integration is needed to enhance its explanatory power.

TPB, articulated by Ajzen (10) has been instrumental in explaining a broad spectrum of behaviors, notably in the realm of health. At the core of this theoretical model lies behavioral intention, which represents the most immediate and powerful determinant of actual behavior, capturing an individual's motivation and commitment to perform a specific action. This theory posits that behavioral intentions are determined through an interplay of three core psychological factors. Attitude toward the behavior represents an individual's overall favorable or unfavorable assessment of performing the specific action. Subjective norms capture the perceived social expectations from important referents and the motivation to comply with these social pressures. Perceived behavioral control incorporates the perceived obstacles or facilitators to performing the behavior and the person's self-efficacy in overcoming potential barriers (10). These factors interact dynamically to influence an individual's likelihood of acting on their intentions, thus playing a critical role in predicting and understanding behavioral change. TPB is esteemed as a suitable theoretical framework due to its robustness and simplicity, demonstrating wide-ranging predictive power for human actions. It has been corroborated in over 1,000 empirical studies, including those examining sex behaviors (30), breast self-examination practices (31).

This study integrated HBM and TPB into a unified theoretical framework to improve and predict behavioral intentions toward HPV vaccination (see Figure 1). Existing research has applied these theories independently, but their combined potential to explain behavioral variance remains underexplored. Drawing on Baranowski's (32) assertion that integrating robust predictors enhances the explanatory power of health behavior models, this study addresses critical overlaps and gaps between HBM and TPB. Notably, constructs such as HBM's perceived barriers and self-efficacy exhibit conceptual alignment with TPB's perceived behavioral control (33). To mitigate multicollinearity risks, these overlapping constructs (i.e., barriers and self-efficacy) are excluded from the integrated model, preserving theoretical distinctiveness. Prior studies comparing the HBM and TPB have predominantly focused on their predictive utility rather than synthesizing their frameworks to elucidate causal pathways (34). This integration is critical, as TPB does not explicitly account for health-specific threat and benefit appraisals central to the HBM. Fishbein and Yzer (35) argue that threat-benefit analyses should inform attitude formation within TPB. These constructs reflect behavioral beliefs, which act as antecedents to attitudes and intentions (36–39). This study examines the interplay between health cognitions and TPB core determinants by unifying these constructs. This approach advances theoretical understanding by delineating how health beliefs catalyze attitude formation and subsequent intention development. This study thus provides a nuanced lens to explore HPV vaccination bridging health-specific cognitions and social-behavioral mechanisms.

Perceived susceptibility involves an individual's subjective evaluation of their likelihood of acquiring a specific disease or health-related condition (20). Rooted in the HBM (8), this construct posits that heightened perceptions of vulnerability to adverse health outcomes motivate individuals to adopt protective behaviors. Empirical studies indicate substantial variability in perceived susceptibility across populations, with elevated risk perceptions consistently linked to greater engagement in preventive actions (40). For instance, Liao et al. (41) demonstrated a significant positive association between perceived susceptibility and affective attitude in the context of influenza vaccination. Extending these findings to HPV vaccination behaviors, the following hypothesis is put forward:

Perceived severity involves an individual's subjective assessment of the potential harm or adverse consequences related to a health-related threat (20). This construct is commonly operationalized through evaluations of the clinical and psychosocial seriousness of a disease or health condition, encompassing both physical outcomes (e.g., pain, disability, mortality) and socio-functional ramifications (e.g., occupational disruption, familial strain) (40, 42). Empirical investigations, such as Bulgurcu et al. (43), demonstrate that heightened threat salience correlates with enhanced motivation to adopt protective behaviors through attitude formation. Recent studies further substantiate this relationship. Chu et al. (44) identified a direct positive association between perceived severity and favorable attitudes toward vaccination, while Lennox et al. (45) highlighted its predictive utility in shaping attitudes toward preventive health technologies. Consequently, the following hypothesis is put forward:

Perceived benefits refer to an individual's evaluation of the potential advantages or effectiveness of adopting health-protective behaviors to reduce disease risk (20). Within HBM, this construct posits that behavioral adoption is driven by the anticipation of tangible outcomes, such as lowered disease susceptibility or avoidance of health complications. In the context of HPV vaccination, perceived benefits may include direct health advantages (e.g., immunity against high-risk HPV strains) and indirect gains, such as reduced long-term healthcare expenditures or enhanced quality of life. The meta-analysis conducted by Janz and Becker (40) demonstrated that in 81% of the studies reviewed, perceived benefits were identified as the second most influential element among the core constructs of the HBM. The scope of perceived benefits extends beyond traditional health contexts. In consumer behavior research, Choi et al. (46) demonstrated that perceived benefits significantly enhance attitudes toward street food consumption. Similarly, Al-Debei et al. (47) revealed that perceived benefits serve as primary drivers of positive attitudes toward online shopping platforms. Recent investigations into health-related behaviors further corroborate this relationship. Yasa et al. (48) discovered that perceived benefits of medical mask usage exerted a positive effect on public attitudes toward mask adoption. According to previous studies, the following hypothesis is put forward:

Within the TPB, attitude is conceptualized as a central antecedent to behavioral intentions and actions, reflecting an individual's favorable or unfavorable evaluation of engaging in a specific behavior (10). Empirical evidence consistently demonstrates that positive attitudinal evaluations increase the likelihood of adopting health-protective behaviors (49–51). In the context of HPV vaccination, numerous studies underscore the predictive utility of attitude. Catalano et al. (49) identified attitude as the strongest predictor of vaccination intentions among male college students. Similarly, Jozkowski and Geshnizjani (50) reported a robust association between favorable attitudes and vaccination intentions in female college students. Askelson et al. (13) revealed that maternal attitudes significantly predicted intentions to vaccinate adolescent daughters. Collectively, these findings affirm attitude as a critical determinant of HPV vaccination. Hence, the following hypothesis is put forward:

Subjective norm, a core construct of the TPB, is shaped by normative beliefs that reflect an individual's perception of significant others' expectations regarding their engagement in or avoidance of a specific behavior (52). Recent studies, such as that by Prasetyo et al. (53), have demonstrated the significant impact of subjective norms on the intention to comply with preventive health measures. In the context of HPV vaccination, several investigations have underscored the influence of subjective norms on individuals' intention to receive the vaccination. Reiter et al. (54) noted that young males who valued peer approval experienced regret for not being vaccinated against HPV and perceived an increased likelihood of vaccination due to perceived risk. Askelson et al. (13) also confirmed that subjective norms influenced mothers' intentions to vaccinate their daughters against HPV. Drawing on prior research, the following hypothesis is put forward:

Perceived behavioral control reflects an individual's confidence in their capability to carry out a particular behavior, which is affected by perceived access to resources, opportunities, and self-efficacy (10). Empirical evidence underscores its predictive validity across health behaviors. A meta-analysis by Cooke and French (55) of 33 studies demonstrated that perceived behavioral control moderately to strongly predicts behavioral intentions, with higher perceived behavioral control correlating with a stronger intention to act. In the context of HPV vaccination, a stronger perceived behavioral control is anticipated to foster a stronger intention to get vaccinated. Numerous studies (13, 56–58) have found that perceived behavioral control has a significant and positive impact on the intention to receive the HPV vaccine. Consequently, the following hypothesis is put forward:

Attitude, a core component in Fishbein and Ajzen's (59) belief-attitude-intention framework, is defined by Casalo et al. (60) as a learned predisposition toward positive or negative evaluations of specific objects. In the present study, attitudes toward HPV vaccine are influenced by an individual's health beliefs and environmental factors. This study used the transmittal approach (61) to elucidate the mediating role of young adult's attitudes toward HPV vaccines. Specifically, it is hypothesized that attitude will intervene in relationship between perceived susceptibility, perceived severity, perceived benefits and the intention to receive HPV vaccination. Extensive research has consistently identified attitude as a primary determinant of behavioral intention across diverse contexts (62–64). Haddock and Maio (65) define attitude as an evaluative judgment directed toward a stimulus object, which aligns with the Stimulus-Organism-Response paradigm proposed by Mehrabian and Russell (66). This paradigm delineates how an individual's response to environmental stimuli. Within this study, the stimulus (dimensions of HBM beliefs) impacts attitude (the organism), which in turn influences the intention to receive the HPV vaccination (the response). Empirical evidence from various settings corroborates the mediating role of attitude, which is shaped by health beliefs such as perceived susceptibility, perceived severity, and perceived benefits (43, 67–70). Accordingly, the following hypothesis is put forward:

The convenience sampling method was employed due to the absence of a comprehensive sampling frame for young adults aged 18–26 in China. This target population was selected for two main reasons. First, catch-up vaccinations are recommended up to the age of 26 (71). Second, in China, individuals under 18 years of age are legally considered minors, with parents typically exercising decision-making authority regarding their children's vaccinations. In contrast, young adults generally have greater autonomy in deciding whether to receive vaccinations. Therefore, this study targets young adults aged 18 to 26 as survey participants.

The research employed a cross-sectional design utilizing a web-based survey platform hosted on www.wjx.cn, with dissemination channels comprising mainstream Chinese social media applications (WeChat and QQ). The privacy of the participants was strictly safeguarded. Data collection was conducted from March 2 to April 5, 2024, with 581 online questionnaires completed. After data cleaning, 516 valid responses were retained. Table 1 presents the demographic characteristics of the participants, which includes information on sex, age, occupation, educational background, scared of needles.

Perceived susceptibility were assessed with six items, adapted from Champion (20): “My chances of getting the HPV virus are great,” “It is likely that I will be infected with the HPV virus,” “I feel that my chances of getting HPV-related cancer in the future are high,” “There is a good possibility that I will get HPV-related cancer,” “I worry a lot about getting HPV-related cancer,” and “In the future, I may get HPV-related cancer.” These items utilized a 5-point Likert scale (1 = “strongly disagree” to 5 = “strongly agree”).

Perceived severity were assessed with six items, adapted from Krawczyk et al. (72): “I think HPV infection is serious,” “If I am infected with HPV, it would be serious,” “If I am infected with HPV, it would significantly affect my life,” “I think HPV-related cancer is a serious illness,” “If I got HPV-related cancer, it would be serious,” and “If I got HPV-related cancer, it would significantly affect my life.” These items utilized a 5-point Likert scale (1 = “strongly disagree” to 5 = “strongly agree”).

Perceived benefits were assessed with three items, adapted from Tatar et al. (73): “I think that the HPV vaccine is effective in helping to prevent diseases caused by HPV,” “I think that the HPV vaccine may be effective in helping to prevent the HPV virus,” and “I think that the HPV vaccine may be effective in helping to prevent HPV-related cancer.” These items utilized a 5-point Likert scale (1 = “strongly disagree” to 5 = “strongly agree”).

Subjective norm were assessed with four items, adapted from Britt and Englebert (74): “Most people who are important to me think I should get the HPV vaccination,” “My parents or family members think I should get the HPV vaccination,” “My friends think I should get the HPV vaccination,” and “People who are important to me influence my decision to have HPV vaccination.” These items utilized a 5-point Likert scale (1 = “strongly disagree” to 5 = “strongly agree”).

Perceived behavioral control were assessed with five items, adapted from De Perio et al. (75): “It is my decision whether to get the HPV vaccination,” “I am confident I could get the HPV vaccination if I wanted,” “I do have the time to get the HPV vaccination,” “I do have the money to get the HPV vaccination,” and “Getting the HPV vaccination does not require a lot of effort on my part.” These items utilized a 5-point Likert scale (1 = “strongly disagree” to 5 = “strongly agree”).

Attitude was measured by four items, adapted from Xiao (70): “For me, getting the HPV vaccine would be useful,” “For me, getting the HPV vaccine would be valuable,” “For me, getting the HPV vaccine would be important,” and “For me, getting the HPV vaccine would be effective.” These items utilized a 7-point Likert scale (1 = “strongly disagree” to 7 = “strongly agree”).

Behavioral intention were assessed with five items, adapted from Gerend and Shepherd (33): “I will try to get more information about HPV vaccination,” “I will consider getting vaccinated for HPV,” “I will try to get vaccinated against HPV,” “I will actually get the HPV vaccination,” and “If the doctor provides me with the HPV vaccine, I will get vaccinated.” These items utilized a 7-point Likert scale (1 = “strongly disagree” to 7 = “strongly agree”).

Partial Least Squares Structural Equation Modeling (PLS-SEM) has advantages in dealing with model complexity, which is more advantageous than covariance-based structural equation modeling. (76). Given the complexity and prediction-oriented nature of the conceptual model in this study, PLS-SEM was deemed the appropriate analytical technique (77, 78). The conceptual model in this study comprises seven latent variables, with six independent variables, one mediator, and one dependent variable, surpassing the mean in terms of complexity and the number of paths and variables, as noted by Hair et al. (76). Akter et al. (79) further supports the superiority of PLS-SEM for analyzing multiple regressions involving numerous independent and intervening variables within a single analytical framework.

Considering the intricate nature of this study's model, SmartPLS 4 (v 4.1.0.3) software was employed to assess the measurement and structural model. In line with Hair et al. (77, 80), evaluating of the reflective measurement model involves testing indicator loadings, internal consistency reliability, convergent validity, and discriminant validity. The subsequent phase involves the structural model assessment upon achieving satisfactory results in the measurement model evaluation. The standard criteria for structural model assessment encompass the Variance Inflated Factor, coefficient of determination (R²), effect sizes (f²), predictive relevance (Q²), and the significance of the path coefficients, ensuring a comprehensive analysis of the model's predictive and explanatory power.

In accordance with the recommendations of Hair et al. (77, 80), the measurement model was evaluated to establish reliability and convergent validity by examining Cronbach's α (>0.7), factor loadings (>0.5), composite reliability (>0.7), and average variance extracted (>0.5). As shown in Table 2, the results indicate that Cronbach's α values range from 0.830 to 0.961. The factor loadings are within the interval of 0.573 to 0.942. The composite reliability values are reasonable, falling between 0.881 and 0.970. Additionally, the average variance extracted values range from 0.556 to 0.864.

Discriminant validity was evaluated using the conservative heterotrait—monotrait (HTMT) ratio approach recommended by Henseler et al. (81), Table 3 confirms all HTMT values below the 0.85 threshold, indicating no discriminant validity issues among the constructs. The results demonstrated that the measurement model satisfies the reliability and validity in this study.

Table 4 presents the values of the determination coefficient (R²) and predictive relevance (Q²). Attitude variance is 29.5% explained by perceived susceptibility, severity, and benefits, while 53.2% of behavioral intention variance is attributable to attitude, subjective norms, and perceived behavioral control. R² values indicated that all external variables have a satisfactory effect on internal dependent variables (77, 78). Moreover, Q² values for a specific endogenous construct should be greater than zero to indicate good predictive relevance (81). As shown in Table 4, all Q² values are greater than 0 (attitude = 0.200, behavioral intention = 0.457), confirming that the PLS-SEM model exhibits good predictive power.

Following Hair et al. (77, 80), all hypotheses were assessed using 5000 bootstrap samples with one-tailed testing. The PLS-bootstrapping results shown in Figure 2 and Table 5 presents that perceived susceptibility (β = 0.109, t = 2.658, p < 0.05), perceived severity (β = 0.456, t = 13.323, p < 0.05), and perceived benefits (β = 0.175, t = 5.413, p < 0.05) have significant positive effects on attitude toward the HPV vaccine. These findings support hypotheses H1, H2, and H3. Besides, subjective norm (β = 0.070, t = 2.407, p < 0.05), attitude (β = 0.397, t = 11.378, p < 0.05), and perceived behavioral control (β = 0.454, t = 11.693, p < 0.05) have significant positive effects on the intention to receive HPV vaccination. Thus, hypotheses H4, H5, and H6 are supported. Besides, the VIF was employed to assess multicollinearity among items. The VIF values ranged from 1.019 to 1.215, indicating no multicollinearity issue.

In this study, the attitude was treated as a mediating effect. The mediation effect was assessed using the bootstrap method proposed by Preacher and Hayes (82), which is endorsed by Hair et al. (80) as a suitable approach for PLS-SEM. As shown in Table 6, Attitude serves as a positive mediator in the relationship between perceived susceptibility (β = 0.043, t-value = 2.598, p < 0.05), perceived severity (β = 0.181, t-value = 8.114, p < 0.05), perceived benefits (β = 0.070, t-value = 4.918, p < 0.05), and intention to receive HPV vaccination. Therefore, hypotheses H7, H8, and H9 are supported.