The monkeypox virus (MPXV) causes a zoonotic disease (mpox) endemic to several African countries.1 By July 2022, the World Health Organization (WHO) declared it a public health emergency of international concern.2 In Spain, a total of 7,521 new cases were reported in 2022 and 325 additional cases in 2023, making Spain one of the most affected countries in the European Union.3

Although MPXV clade IIb is self-limited, a small proportion of cases require hospitalization (7%), with a case fatality rate of 0.1%.4 The clade IIb MPXV outbreak primarily spread through close physical contact (which often takes place during sexual encounters but is not strictly limited to sexual transmission), with most cases involving men, particularly gay, bisexual, and other men who have sex with men (GBMSM), aged 30-50 years.4–6 In response to the rapid rise in cases, swift actions were taken, including surveillance, contact tracing, and vaccination of high-risk groups.2,7 In Spain, vaccination began in June 2022, although initial vaccine availability was limited.8 As a result, individuals engaging in high-risk sexual behaviours —such as having multiple partners or participating in group sex— were prioritized for pre-exposure prophylaxis, particularly GBMSM, along with those with occupational exposure risks and individuals living with HIV or on PrEP.8

Vaccination played a key role in controlling the outbreak, together with the reduction in the susceptible population following a high number of infections and behavioural changes among higher-risk groups, partly driven by risk communication efforts.9 Nevertheless, vaccine uptake varied globally due to differences in availability, accessibility, and national policies.10 A meta-analysis found that global vaccine uptake stood at only and 30.9%, with Europe having the highest rate at 33.5%.10 Within Europe, a study conducted in the United Kingdom observed a significantly higher uptake of 69%.11 In the case of Spain, although there are no specific studies quantifying the percentage of vaccinated individuals, available data indicate that, by December 2022, over 25,000 vaccine doses had been administered, including both partial and complete doses.12

To date, no data are available regarding mpox vaccine uptake, intention, and the associated factors during the 2022-2023 outbreak within the Spanish context. This underscores the importance of identifying the factors associated with mpox vaccine uptake and intention in a context of vaccine availability, to inform strategies aimed at increasing vaccination coverage. The Health Belief Model provides a theoretical framework to understand preventive health behaviours, including vaccination, by positing that individuals’ actions are influenced by a combination of background or modifying factors, health-related beliefs, and cues to action.13 First, modifying factors, including sociodemographic characteristics, health-related behaviours, and psychosocial factors, shape individuals’ beliefs about a health threat. Second, health-related beliefs, such as perceived susceptibility, perceived severity, and perceived benefits and barriers to action, determine motivation to engage in preventive behaviours. Third, cues to action represent external or situational triggers that can activate the decision to adopt a preventive behaviour. Together, these components offer a structured approach to examining how individual, social, and contextual factors interact to influence health-related decision-making. Complementarily, access-oriented frameworks such as Tanahashi's model emphasise that effective health services coverage (such as vaccination) depends not only on individual motivation and availability, but also on the acceptability of services, which may be shaped by broader psychosocial and social barriers.14

In the context of mpox, relevant modifying factors include sociodemographic characteristics, health-related factors such as HIV status or PrEP use, and psychosocial factors including perceived stigma, which can act as a barrier to access health services due to fear of social judgment.10 Health-related beliefs encompass worry about mpox, perceived susceptibility to infection, and perceived severity of the disease, which together shape individuals’ motivation to vaccinate. Finally, cues to action include sexual behaviours that may increase perceived exposure risk, as well as receiving mpox-related information from healthcare professionals, both of which can trigger preventive actions such as vaccination.15,16

Therefore, this study pursues two objectives: 1) to estimate the prevalence of mpox vaccine uptake and its associated factors among GBMSM in Spain; and 2) to examine, among those who were not vaccinated, their intention to receive the vaccine and the factors linked to that intention.

In this study, 38% of GBMSM of our sample reported having received the mpox vaccine, while 91.7% of unvaccinated individuals expressed high likelihood to do so. The results suggest a gap between intention and uptake, with vaccination uptake mainly associated with sociodemographic and behavioural factors (such as age, urbanicity, PrEP use, and sexual activity) whereas vaccination likelihood was primarily linked to psychosocial variables, including concern about infection and perceived severity.

Young people (those under 30 years old) and older people (those aged>50 years old) were less likely to be vaccinated than those aged 30-49 years old. These findings are consistent with other studies, where young individuals reported less mpox vaccination uptake.11,15,21 Studies suggest that they could have less perception of severity and could be less linked to health services, which can be associated with lower access to mpox information and prevention measures, such as vaccination.21,22 Moreover, they can also experience more stigma, which also acts as a barrier to seek medical attention and diagnosis disclosure.23. For the older age group (>50 years), lower vaccination prevalence may be partly explained by the fact that they were not a prioritized group, as many individuals in this cohort received smallpox vaccination during childhood.

Participants residing in large municipalities (≥500,000 inhabitants) reported higher levels of vaccination uptake. This finding aligns with previous research24 and may be related to territorial disparities in access to healthcare. Less urbanized areas often lack specialized health services,25 which can limit the availability and accessibility of vaccination. Additionally, GBMSM living in rural or less urban settings may experience heightened levels of stigma, which has been described as a barrier to seeking care.26,27 In addition, the intradermal administration of the mpox vaccine in the forearm can leave visible marks,28 which have been described as stigmatising and associated with fears of being identified or judged.24

Use of PrEP, living with HIV and having more than 2 sexual partners in the last 6 months were also associated with higher vaccination uptake, in line with findings from previous studies.10,11,15,29 This association is consistent with vaccination strategies that prioritized individuals at elevated risk, such as people with multiple sexual partners, those who were on PrEP and people living with HIV.12 Furthermore, having attended a gay nightclub one or more times in the last six months was also associated with higher vaccination uptake. This finding may also reflect public health strategies that prioritized vaccination for individuals engaging in higher-risk practices,12 such as attending SOPV. In addition, information campaigns conducted in nightclubs (for example, through posters or outreach activities led by community-based organisations) may have further contributed to this association. Also, based on previous literature, attending SOPV has been associated with increased risk perception, which has in turn been associated with higher motivation.29

However, in our study, beliefs related to mpox were not significantly associated with actual vaccination uptake. Interestingly, beliefs were significantly related to the intention to get vaccinated. One possible explanation could be that perceived severity and concern about mpox are associated with individuals’ motivation and intention, but not necessarily linked with preventive actions. This finding may reflect the well-established gap between intention and behaviour, as described in health behaviour theories such as the theory of planned behaviour.30 While intentions are largely shaped by individual beliefs and perceptions, actual behaviour is also conditioned by the subjective norms within the community —specifically, the perceived social acceptance and support for vaccination among GBMSM. Social normalization of the vaccine can be a decisive factor in increasing intention; however, this motivation often remains latent when faced with external and structural factors, including access to services, logistical obstacles, or fear of stigma.

Specifically, our findings regarding healthcare provider advice illustrate this complexity. Such advice may be insufficient to bridge the intention-behavior gap unless supported by public health campaigns that promote visibility, legitimize the process, and reinforce the vaccine's importance within the community. Moreover, the influence of professional recommendations is contingent on a consistent link with the health system. For marginalized individuals, the absence of this connection means that verbal advice alone cannot overcome logistical barriers or systemic mistrust. To be effective, clinical recommendations must be paired with direct, low-barrier access and communication strategies that strengthen the social normalization of vaccination among GBMSM. This phenomenon is not unique to mpox. Previous studies in the context of the vaccination against the COVID-19 have shown that even highly motivated individuals may not act on their intentions when faced with such barriers.31 In the case of mpox, sociodemographic factors, such as socioeconomic status and education level, significantly influence mpox vaccination access, with higher education and income associated with increased uptake.10,11 Moreover, contextual factors, including territorial inequalities and perceived stigma, further hinder access, widening the gap between vaccination intention and actual uptake.26,27

A subgroup of particular relevance in our study comprises unvaccinated individuals who reported a low likelihood of receiving the mpox vaccine. This group represents a critical challenge for public health strategies, as they remain unprotected while simultaneously exhibiting lower responsiveness to conventional vaccination messaging. In our sample, individuals with low vaccination likelihood reported significantly lower concern about contracting mpox, as well as lower perceived risk and severity of infection, and were more likely to view mpox as little or not at all problematic in terms of social consequences. In addition, this group demonstrated lower levels of mpox-related knowledge, and more frequently expressed disagreement or neutrality toward recommended prevention strategies. These findings are consistent with previous research showing that individuals who are vaccinated or willing to be vaccinated tend to be better informed about mpox than those who exhibit vaccine hesitancy or unwillingness.32,33

This is the first nationwide study in Spain to assess mpox vaccine uptake and likelihood to vaccinate among GBMSM, expanding beyond prior regional research focused mainly on sociodemographic and clinical aspects.34 In contrast, our study includes a broader national sample and integrates psychosocial, stigma-related, health, and behavioural variables, offering a more comprehensive description of vaccine-related dynamics in this population. This distinction is crucial for understanding the motivational versus structural factors associated with vaccination and the intention–behaviour gap in health behaviour theory.

Despite these strengths, several limitations should be acknowledged. First, the overall sample size, while adequate for primary analyses, limits the statistical power for subgroup analyses, particularly those related to the second objective of the study, which focused on individuals expressing lower likelihood to vaccinate. The small size of this reference group constrains the generalizability of findings and may limit the identification of significant associations. Another potential limitation is the non-probabilistic nature of the sample, which may lead to selection bias. Individuals with greater digital access, higher digital and health literacy, higher engagement with health services, higher educational and economical level, or stronger connections to community networks could be overrepresented, and therefore more likely to be vaccinated, potentially leading to an overestimation of mpox vaccination uptake in our sample. For these reasons, self-reported vaccination coverage in this study should not be interpreted as a population-level estimate. Instead, it must be contextualized within the specific target population for vaccination —namely, individuals eligible for the vaccine due to their high-risk sexual practices and lack of prior immunity (either from smallpox vaccination or previous mpox infection). Additionally, the use of a convenience sample with a limited sample size means that the study population is not representative of the broader Spanish GBMSM population. These limitations should be considered when interpreting the results.

Moreover, the cross-sectional design of the study precludes any inference of causality. Furthermore, as with many self-reported surveys, the possibility of information bias (such as social desirability or recall bias) must be considered, especially given the sensitive nature of the topic. Lastly, the data were collected during a specific moment of the outbreak, and vaccination dynamics may evolve over time depending on epidemiological trends, policy shifts, or changes in public perception, limiting the temporal generalizability of the findings.

Nonetheless, the insights derived from this study are timely and actionable, and they highlight areas that may inform tailored public health strategies that address both vaccination willingness and barriers related to translating intention into action. This suggests the relevance of considering both motivational components (through comprehensive and non-stigmatizing communication led by trusted healthcare professionals) and structural barriers, including stigma, socioeconomic disadvantage, and territorial disparities in healthcare access. Addressing these challenges is essential to ensure equitable vaccine access and to reduce the persistent gap between intention and behaviour in the context of mpox prevention.

Vaccination campaigns targeting GBMSM may play a role in addressing the intention-behaviour gap. Based on our findings and existing literature, several key recommendations can be made to enhance these efforts. Firstly, communication strategies should be led by trusted sources by the GBMSM community, particularly healthcare professionals, official public health institutions, community-based organisations and NGOs, as receiving information from these actors was positively associated with vaccine uptake in our study and others.10,22,29 Messaging from credible and reliable sources has been described as enhancing trust and counteract misinformation, especially in communities that may face systemic marginalization.

Secondly, addressing structural barriers requires a multidimensional approach, such as Tanahashi's framework,14 which defines access through geographic accessibility, acceptability, and appropriateness. In rural or less urbanized areas, lower uptake may reflect not only scarce specialized services (geographic accessibility) but also significant challenges in acceptability. In these settings, the fear of stigma is compounded by institutional stigma and unintentional discrimination within healthcare systems, where a lack of anonymity can deter individuals from disclosing high-risk behaviors or requesting vaccination.28,35

As emphasized in the Spanish Strategic Plan for the Prevention and Control of HIV and STI 2021–2030, addressing these systemic biases is essential to improve prevention efforts.36 Consequently, strategies must go beyond proximity; they must ensure confidentiality and staff training to create stigma-free environments. Implementing mobile clinics and community-led outreach in partnership with NGO could provide more discreet “low-threshold” access points, effectively bridging the gap between vaccination intention and actual behavior in marginalized or less urbanized contexts.22 However, the use of non-habitual vaccination settings also entails logistical challenges, including ensuring adequate cold-chain management, standardized clinical protocols, trained personnel, and integration with existing health information systems for dose registration and follow-up. Addressing these operational considerations is essential to maximize the effectiveness and sustainability of community-based vaccination strategies.

Nevertheless, our findings suggest that low vaccination likelihood among unvaccinated individuals may be driven by broader motivational factors and information regarding mpox rather than by structural barriers alone. In this context, expanding vaccine availability is unlikely to be sufficient to substantially increase uptake in this group. Consequently, interventions aimed at increasing vaccine uptake among individuals with low likelihood of vaccination should prioritize improving the availability, clarity, and relevance of mpox-related information.24 Moreover, further research is needed to better understand the information sources they rely on, their engagement with LGBTIQ+community organizations, and other potential informational barriers that may limit exposure to preventive messaging.

Finally, information campaigns must be comprehensive and clearly explain the risks of infection and the benefits of vaccination, while avoiding stigmatizing language or moralizing tones.24 It is critical that these campaigns do not reinforce negative stereotypes about GBMSM but instead promote a rights-based, inclusive approach that encourages preventive health behaviours without fear or shame.22

In this first national-level analysis of mpox vaccination among GBMSM in Spain, uptake was reported at 38.0%, while 91.7% of those unvaccinated indicated a high intention to receive the vaccine. There is a substantial gap between actual vaccination and expressed intention among the unvaccinated. While structural and behavioural factors (such as age, urbanicity, PrEP use, and sexual activity) were associated with vaccine uptake, likelihood to vaccinate was primarily associated with psychosocial perceptions, including concern about mpox and perceived severity of infection. These findings highlight the relevance of considering both motivational and structural barriers to vaccination. Enhancing communication through trusted health professionals, expanding access in less urbanised areas, and combating stigma may represent relevant strategies to address barriers related to translating intention into action. Furthermore, interventions should adopt a rights-based, community-informed approach that promotes equity and avoids reinforcing stereotypes. Such efforts are essential to ensure that high-risk populations are not left behind in future public health responses.

The datasets generated during the current study are not publicly available due to the legal and data protection restrictions established in the inter-institutional collaboration agreement of the LIBERO-POX project. However, they are available from the corresponding author upon reasonable request, subject to the presentation of a formal analysis proposal and approval by the project's Steering Committee.

Rocío Zurriaga-Carda.

The corresponding author, on behalf of the other authors guarantee the accuracy, transparency and honesty of the data and information contained in the study, that no relevant information has been omitted and that all discrepancies between authors have been adequately resolved and described.

The authors confirm that we meet the criteria for authorship. Conceptualization and study design: H. González-Casals and C. Folch. Data collection and analysis: H. González-Casals, H. Martínez-Riveros, N. Lorente, L. Villegas, J. Mena, O. Apffel-Font, J. Casabona, P. Meireles and C. Folch. Writing, original draft: H. González-Casals. Writing, review and editing: H. González-Casals, H. Martínez-Riveros, N. Lorente, L. Villegas, J. Mena, O. Apffel-Font, J. Casabona, P. Meireles and C. Folch. Final approval of the version to be submitted: H. González-Casals, H. Martínez-Riveros, N. Lorente, L. Villegas, J. Mena, O. Apffel-Font, J. Casabona, P. Meireles y C. Folch. Each author has contributed substantially to the work, has reviewed and approved the final version of the manuscript, and agrees to be accountable for all aspects of the work to ensure that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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