In our study, we found that respondents generally favored vaccination, with a refusal prevalence of 16.8%. This rate aligns with published data on the intention to refuse the COVID-19 vaccine in the Catalan population during the same year as the study. This indicates that the vaccine hesitancy observed in our sample is consistent with broader regional trends. Additionally, within this inquiry, we detected an increase in doubts about vaccines as a result of the pandemic [16], which mirrors global trends of heightened vaccine skepticism fueled by misinformation and rapidly evolving scientific guidelines during the COVID-19 crisis.
Although official data regarding vaccine rejection are not at our disposal, we do have authoritative records delineating vaccine acceptance trends. These records evince that vaccination coverage rates in Spain for the years 2021 and 2023 remained comparably stable. Notably, in 2024, a marginal augmentation in vaccination coverage for MMR and hexavalent vaccines was observed. This suggests a positive trend in the uptake of these essential vaccines, possibly due to public health campaigns and increasing public awareness of the benefits of vaccination. However, this positive trend was contrasted by a diminished coverage for influenza compared to the year 2021 [12]. Therefore, we believe the data on hesitancy and refusal of vaccination could be valuable in the current scenario of vaccination in Spain in 2024, as it highlights areas needing targeted interventions to improve vaccine uptake and address ongoing public concerns about vaccine safety and efficacy
The SAGE Vaccine Hesitancy Working Group categorize vaccine hesitancy using a matrix of contextual influences, individual/social influences, and vaccine and vaccination specific issues [4, 17].
Our study delved into several contextual influences, particularly focusing on the sociodemographic and sociocultural characteristics of the population. Analysis of respondent age revealed higher rates of vaccine refusal among those over 60 years old. This does not coincide with previous findings from other studies, where a greater likelihood of vaccination was detected in older people because of increased health concerns and susceptibility to illness [11, 18–21]. We believe that the reason for this finding may stem from the significant rejection in our older population of the influenza vaccination, which is primarily targeted at people over 65 years old or with underlying pathologies in Spain, and from the difficulties already described in previous publications to achieve satisfactory vaccination coverage against influenza [21–24]. We also detected greater hesitancy among people under 30 years old, particularly due to concerns about diseases associated with vaccines and the cost of vaccines. This finding is consistent with previously published studies [11, 18–21, 25] and underscores the need for vaccination campaigns tailored to specific age groups, addressing their unique concerns and barriers.
When considering sex, our study revealed that women and parents with children under 15 years old, showed greater hesitancy due to the components of vaccines or diseases that have been associated with vaccines. Greater doubts were detected in women without children under 15 years old than in men. Moreover, women were more likely to refuse vaccines for their children, aligning with previous studies, which show a greater predisposition to vaccination in men than in women, and less acceptance and greater hesitancy in parents [11, 18, 26, 27]. Concretely, women with young children are more concerned about vaccinating their children, necessitating targeted strategies to bolster the trust and confidence, as previously proposed [11, 18, 27, 28].
Regarding education level, individuals without a university education exhibited greater hesitancy due to associated diseases or vaccine payment. This aligns with published studies that show that the higher the level of education, the greater the acceptance of vaccines [11, 18, 20, 23, 29].
Cultural, religious, and family beliefs emerged as influential factors associated with hesitancy and decision about vaccination, with a greater predisposition to get vaccinated if the sociocultural environment is provaccine. These results echo findings from prior studies [3, 10, 18].
In terms of political and policy-related contextual influences, most respondents favoured free and compulsory vaccination, except those who refused vaccines or expressed hesitation because of components, associated diseases, or payment for vaccines. Although in recent years there has been growing traction for anti-vaccine movements, most of the population seems to be in favour of compulsory vaccination policies, as evidenced in a 2019 review. Moreover, it seems that support towards mandatory policies increases after their implementation [30]. Nonetheless, efforts to improve vaccine acceptance, such as enhancing education and providing proof of the efficacy, benefits and safety of vaccines, remain crucial [31].
We observed greater vaccine refusal and hesitancy among individuals who deemed health professionals or websites unreliable sources of vaccine information, while considering friends, family, or social networks as reliable sources. These results reinforce previous publications which stated that the crisis in the vaccination system and the resurgence of anti-vaccine movements are due to the increased accessibility of information and the reduced credibility of HCPs [5, 32]. Exposure to anti-vaccine content on social media was associated with refusal and hesitancy to vaccinate [33–37], highlighting the critical need to combat misinformation to mitigate its effects [35, 36].
Our study also suggests that a lack of trust in HCPs is associated with greater vaccine refusal and hesitancy. This aligns with existing reviews and published studies that conclude that vaccine safety and trust in health authorities are the main factors in promoting vaccine acceptance [11, 38]. According to the WHO's "3Cs" model (confidence, compliance, convenience), confidence in vaccines and in the healthcare system constitute one of the three main determinants of vaccine hesitancy [4, 7, 17].
We detected a greater refusal of the vaccines for influenza, tetanus, papilloma, and varicella (chicken pox). Mostly individuals refused vaccines for themselves and, to a lesser extent, their children. These findings mirror other international studies which highlight the difficulties in achieving satisfactory vaccination coverage for influenza and papillomavirus [31, 36, 39]. Data published by the Spanish Ministry of Health also corroborate these difficulties in vaccination coverage for influenza, papilloma, and varicella in 2021–2022. In Spain, the recommendation to maintain vaccination coverage ≥ 95% for MMR vaccination in 2021–2022 was not achieved [12] and the goal of maintaining measles and rubella elimination status was not met [40]. Again, although there are high coverage rates for tetanus in primary vaccination with the hexavalent vaccine, vaccination coverage with Td decreases in adolescents [12]. In our study, we found a greater refusal of tetanus vaccine than the diphtheria vaccine, although tetanus and diphtheria vaccines are usually administered together. We attribute this difference and other similar ones to a possible lack of knowledge of the vaccination schedule in our reference population or to a greater popular knowledge of tetanus vaccine because of its indication for administration in certain wounds.
Our study revealed a relationship between having hesitancy due to vaccine components and refusing a vaccine. It also showed that having hesitancy due to vaccine components or associated diseases were associated with hesitancy due to vaccine payment. Earlier research has found that accessibility and cost, along with safety and efficacy were reasons for hesitancy [11, 17, 41]. In most Spanish autonomous communities, the Meningococcal ACWY and Meningococcal B vaccines are now part of the public vaccination schedule and thus should no longer be a reason for hesitancy because of costs in these cases [42].
Collective responsibility was assessed and greater refusal and hesitancy was detected in respondents who were unaware that individual vaccination protects the community. The concept of collective responsibility was one of five factors that affect people’s perception of vaccines, along with confidence (trust in vaccine efficacy and safety), complacency (perception about the risk of the disease), calculation (weighing the risks and benefits of vaccines) and constraint (accessibility of information about the vaccine). These are part of the 5Cs model [38], which extends from the 3C model introduced by the WHO SAGE Working group [4].
We intended to study the profile of the local population with vaccine hesitancy and we observed heightened hesitancy among people who disagreed with cow's milk consumption or the use of infant milk formulas, and those who adhered to a non-Mediterranean diet or favoured alternative or complementary treatments for healthcare. This profile of a population with a preference for natural therapies, skepticism towards established scientific positions, and greater reticence towards healthcare systems and HCPs, seems to be the profile of vaccine hesitancy detected in primary care. In another study published in the UK in the same year, rejection and hesitancy towards vaccination were also associated with low confidence in the health service [25]. To address vaccine hesitancy, we urge institutions and governmental bodies to seek strategies to enhance trust in HCPs, public health systems, authorities, and health policies. Encouraging shared participation in the formulation of vaccine recommendations is paramount [38]. Additionally, as previously suggested by some authors, novel approaches such as analysing population opinions on vaccination through social networks using artificial intelligence to complement traditional survey methods, can provide a more comprehensive understanding of vaccine refusal and hesitancy dynamics and allow targeted interventions. Such initiatives can facilitate effective engagement with diverse communities and foster informed decision-making regarding vaccination [34, 43–46].
One of the limitations of this study is the inherent recruitment bias associated with the online survey method, which restricted participation to individuals with internet access. This can produce selection bias problems because there are different probabilities of being involved in the study depending on where people live, their level of education, and their age. Therefore, this may hinder the generalization of the results. However, given that 96.1% of Spanish households have internet access and 85% of Spaniards are users of social networks [47, 48], the reach of our survey remains substantial. Another possible limitation is potential respondent repetition, although, we anticipate minimal impact on the final results because of expected low rate of repetition. Additionally, our sample skewed towards women and people with a university education, this could limit the interpretation and generalization of our study to the broader population. Finally, reaching the anti-vaccine population posed challenges, as interactions with these groups is difficult. To mitigate eventual bias deriving from this, in our sample size calculation, we considered that the proportion of antivaccine responses would be much lower than the proportion of pro-vaccine responses. Despite these limitations, our study provides valuable insights into vaccine refusal and hesitancy, but caution is warranted in extrapolating findings to the entire population.