Vaccine Hesitancy

Vaccine hesitancy is defined by the World Health Organization's Strategic Advisory Group of Experts (WHO SAGE) as a delay in acceptance or refusal of vaccination despite availability of vaccination services ^[1]D5[2]C4. Also referred to as vaccine uncertainty or immunization hesitancy, this construct encompasses a spectrum of behaviors ranging from full acceptance of all recommended vaccines, through selective acceptance or delay, to outright refusal of all vaccines. It is not a binary state but a continuum influenced by cognitive, emotional, social, and structural factors ^[1]D5[3]C4. This distinction is critical: vaccine hesitancy differs fundamentally from antivaccination movements, which represent active, organized opposition to vaccination based on ideological or pseudoscientific beliefs. Hesitancy involves uncertainty, doubt, or practical barriers, not necessarily rejection of the principle of vaccination ^[1]D5.

The Hesitancy Continuum

The WHO SAGE model places vaccine hesitancy on a gradient between full acceptance and complete refusal. Individuals may be fully accepting, hesitant (with delays or doubts about specific vaccines), or refusing altogether. This continuum is dynamic, a person may move along it depending on the vaccine, the context, and their evolving perceptions ^[1]D5[2]C4. For example, a caregiver may accept routine childhood vaccines but delay or decline a novel vaccine like the COVID-19 vaccine due to concerns about novelty or safety ^[1]D5[4]A1b. The continuum explains why interventions must be tailored: a one-size-fits-all message may not move a hesitant individual toward acceptance.

Distinction from Antivaccination Movements

Vaccine hesitancy should not be conflated with antivaccination movements , which are characterized by active, often vocal opposition to vaccination as a practice. Antivaccination activists reject the scientific consensus and may spread misinformation. In contrast, hesitant individuals are open to information and may be influenced by trusted sources, including healthcare providers ^[1]D5[2]C4. The clinical implication is that most hesitant patients can be counseled effectively, whereas those with entrenched antivaccination beliefs may require different strategies ^[1]D5.

The 3Cs Model and Extensions

The WHO SAGE working group operationalized the conceptual framework of vaccine hesitancy through the 3Cs model: Confidence, Complacency, and Convenience (or Constraints) ^[2]C4[3]C4. This model provides a structured way to assess the underlying drivers of hesitancy in clinical and public health settings.

Subsequent research has expanded the 3Cs to a 5Cs model (Confidence, Complacency, Constraints, Calculation, and Collective responsibility) to capture additional dimensions such as the individual's calculation of risks and benefits and the perceived duty to protect the community ^[3]C4. The 5Cs model has been particularly useful in understanding hesitancy in low- and middle-income countries, where contextual factors like miscommunication and knowledge gaps are prominent ^[3]C4.

These conceptual frameworks set the stage for understanding the scale of the problem. Global COVID-19 vaccine hesitancy rates between 2020 and 2022 illustrate the variation: using the definition that includes both behavior and willingness, hesitancy rose from 18.8% in 2020 to 29.1% in 2021 and 30.8% in 2022, with the highest rates in Africa (42.0%) and the lowest in Europe (16.5%) ^[6]B2a. The next section examines the epidemiology and prevalence of vaccine hesitancy across populations and settings.

Pearl: When a patient expresses doubt about a vaccine, do not assume they are oppositional, assess the specific component of the 3Cs (confidence, complacency, or convenience) causing the hesitation, as this directly guides the counseling approach ^[2]C4[3]C4.

The prevalence of vaccine hesitancy varies substantially by population, vaccine type, and geographic region, with estimates ranging from 15% to over 40% among adults in high-income settings. In a US caregiver survey, 40.9% reported childhood vaccine hesitancy ^[11]C4. Among Alaska adults, only 34% had received the first COVID-19 vaccine dose, and uptake declined sharply with each subsequent booster, reflecting widespread hesitancy ^[12]C4. In Sweden, vaccine acceptance scores differed significantly by region of birth: vaccinated individuals from Sweden and Western countries scored 9.5 and 8.9 points higher, respectively, than their unvaccinated counterparts, versus only 2.8 points higher among those from non-Western countries ^[10]C4.

Temporal Trends

During the initial COVID-19 vaccine rollout (December 2020-May 2021), positive sentiment on Twitter declined from 18.3% to 10.9%, while negative sentiment rose from 9.1% to 14.6% ^[13]C4. A critical inflection point occurred in February 2021. Notably, negative sentiment toward childhood vaccination surged from 6.7% to 43.3% by April 2021, suggesting spillover of COVID-19 vaccine distrust into routine immunizations ^[13]C4.

Demographic Distribution

Vaccine hesitancy varies by age, sex, sexual orientation, and geography. In Alaska, young adult males exhibited the highest hesitancy, while lesbian, gay, bisexual, and transgender individuals had the lowest ^[12]C4. In the UK, adolescents were influenced mainly by media and social norms, whereas older adults were driven by safety concerns and trust in health professionals ^[1]D5. Education shows an asymmetric gradient: schooling is strongly associated with higher COVID-19 vaccine uptake in Central and Eastern Europe but only weakly in Western Europe, a pattern attributed to institutional legacies of communist rule ^[16]C4.

Risk Factors for Vaccine Hesitancy

Multiple factors predict hesitancy, with trust in the healthcare system emerging as the strongest correlate across diverse populations ^[12]C4. Political affiliation is a robust predictor: conservative caregivers had higher odds of childhood vaccine hesitancy compared with moderate and liberal caregivers ^[11]C4. Among older adults in Korea, lower confidence in COVID-19 vaccination and higher complacency were associated with lower coadministration of COVID-19 and influenza vaccines ^[14]C4.

These risk factors interact across the lifespan and are compounded in vulnerable subgroups, including immigrants and those with lower health literacy ^[1]D5. Understanding these patterns is essential for targeting interventions, as discussed in the next section on determinants and causes.

Pearl: The single strongest predictor of vaccine hesitancy is low trust in the healthcare system ^[12]C4; clinicians should prioritize building trust before delivering vaccine-specific information.

The prevalence of vaccine hesitancy varies widely, but its drivers are consistently multifactorial and context-dependent. Understanding these determinants is essential for designing effective interventions. The evidence converges on a core set of interrelated factors that span individual beliefs, social dynamics, historical experiences, and system-level barriers.

The 3Cs Model as an Organizing Framework

The WHO Strategic Advisory Group of Experts (SAGE) proposed the 3C model, confidence, convenience, and complacency, which remains the most widely used framework for classifying determinants. A systematic review of parental vaccine hesitancy for childhood immunizations across Europe found that trust in healthcare professionals (HCPs) emerged as a key factor across studies, while fear of side effects, logistical barriers, and low perceived disease risk negatively influenced decisions ^[18]C4. In the UK, a systematic review of 50 studies (87.5% on COVID-19 vaccines) identified all SAGE themes at the system level, most notably vaccine novelty, the media environment, and health system experiences ^[1]D5. At the individual level, vaccine-specific beliefs and knowledge were the most frequently identified perceptual influences ^[1]D5. Together, these findings illustrate that the 3C model captures the major categories but that determinants interact and compound, particularly in vulnerable subgroups ^[1]D5.

Historical and Systemic Distrust

Distrust in healthcare systems, governments, and pharmaceutical companies is a recurring theme across centuries. A historical review tracing anti-vaccine sentiment from the smallpox era through the COVID-19 pandemic identified three persistent drivers: concerns about vaccine safety, distrust of institutions, and objections grounded in personal liberty ^[24]D5. The 1998 Wakefield publication linking MMR vaccine to autism caused a lasting decline in trust that persisted even after scientific refutation ^[24]D5. The COVID-19 pandemic marked a critical inflection point, with hesitancy becoming increasingly politicized ^[24]D5. In sub-Saharan Africa, mistrust of governments was identified as a key factor ^[20]C4. In Indonesia, stakeholder consultations for a new TB vaccine highlighted halal certification concerns and misinformation as major challenges, along with limited healthcare worker knowledge ^[25]D5. Region of birth also matters: in Sweden, individuals from non-Western countries showed weaker associations between vaccine acceptance scores and uptake, suggesting that conventional determinants may not fully explain hesitancy in this group ^[10]C4. In Germany, having a migration background was independently associated with lower vaccination willingness (OR 0.39) ^[26]C4.

Social and Demographic Determinants

Demographic factors are not generalizable across countries due to methodological and contextual differences ^[18]C4, but certain patterns recur. In sub-Saharan Africa, young age, rural location, and low educational attainment were consistently associated with hesitancy ^[20]C4. In Germany, older age (OR 1.02 per year), higher socioeconomic status (OR 1.26), chronic disease (OR 1.32), and high health literacy (OR 1.28) were associated with higher willingness, while moderate health literacy was linked to reluctance (OR 0.76) ^[26]C4. In South Asia, HPV vaccine hesitancy was driven by lack of awareness about cervical cancer and HPV, socio-cultural taboos, religious beliefs, and inadequate healthcare guidance ^[22]C4. In Uganda, among people living with HIV, those unvaccinated (17%) primarily cited fear of side effects (42%) and belief that vaccination increased infection risk (16%) ^[23]C4. Notably, children's vaccine intentions are highly concordant with parents': in a Canadian cohort study, 95% of children's intentions aligned with parents' uptake, and hesitancy among children was 48% in families with unvaccinated mothers versus 5% with vaccinated mothers ^[21]B2b.

Information Environment and Misinformation

Modern digital platforms have transformed the dissemination of vaccine-related misinformation. A social media analysis of 77,171 tweets from December 2020 to May 2021 found a decline in positive sentiment from 18.3% to 10.9% and an increase in negative sentiment from 9.1% to 14.6%, with a critical inflection point in February 2021 ^[13]C4. Negative sentiment toward childhood vaccination rose sharply from 6.7% to 43.3% by April 2021 ^[13]C4. Eight misinformation categories were identified, including claims about DNA alteration, government control, and 5G connectivity ^[13]C4. Users with larger follower counts contributed more negative content, amplifying skepticism ^[13]C4. The COVID-19 pandemic demonstrated that misinformation can be economically incentivized through monetized online content ^[24]D5. Algorithms that prioritize emotionally engaging content further accelerate spread ^[24]D5.

Vaccine-Specific Concerns

Across all populations, concerns about safety and side effects are the most consistently reported vaccine-specific drivers. Fear of side effects was the primary reason for hesitancy among unvaccinated PLHIV in Uganda (42%) ^[23]C4 and a key factor in European parental hesitancy ^[18]C4 and sub-Saharan Africa ^[20]C4. Doubts about vaccine efficacy and beliefs that vaccines increase infection risk also appear repeatedly ^[23]C4[20]C4. In South Asia, fear of ill effects was a major barrier ^[22]C4. The COVID-19 pandemic introduced novel concerns about speed of development and mRNA technology, which were amplified by the information environment.

Determinant Interactions and Context Dependence

No single determinant acts in isolation. The evidence consistently shows that factors interact, for example, low health literacy may compound misinformation exposure, and historical distrust may be activated by novel vaccine technologies. The 3C model provides a useful organizing framework, but effective strategies must be tailored to the specific determinants operating in a given population. As the systematic review on European parental hesitancy concluded, vaccine hesitancy remains "multidimensional and context-dependent" ^[18]C4.

Pearl: Addressing vaccine hesitancy requires targeting multiple determinants simultaneously; single-focus interventions (e.g., education alone) are less effective than multi-component strategies that include trust-building, community engagement, and practical access improvements.

The determinants of vaccine hesitancy, distrust, misinformation, and access barriers, translate directly into measurable harms at the population level. Even modest refusal rates can erode herd immunity and trigger outbreaks of vaccine-preventable diseases , while disparities in uptake perpetuate inequities in disease burden.

Outbreaks and Resurgence of Vaccine-Preventable Diseases

Vaccine hesitancy has been directly linked to the resurgence of diseases once under control. In Turkey, a retrospective study of 2,786 children found that 3.7% had at least one vaccine refusal, with early-onset refusals (median age 1 month post-pandemic vs. 12 months pre-pandemic) strongly associated with multiple refusals (p<0.01) ^[27]B2b. Such clustering of unvaccinated children creates pockets of susceptibility that can sustain transmission. During the COVID-19 pandemic, childhood vaccination rates declined sharply in low- and middle-income countries (LMICs), with most studies reporting a negative or neutral effect on vaccine acceptance for non-COVID-19 vaccines ^[29]B2a. These vaccination gaps increase the risk of measles , polio, and diphtheria outbreaks, particularly in settings with weak health systems.

Erosion of Herd Immunity

Herd immunity requires vaccination coverage of 90-95% for highly contagious diseases like measles. Even a small decline in uptake can have outsized effects. In the Turkish cohort, refusal rates remained stable at approximately 3.7% before and after the pandemic, but the shift toward earlier refusals suggests that infants are increasingly left unprotected during the most vulnerable period ^[27]B2b. In Saudi Arabia, only 6% of women had completed the HPV vaccine series, and 56.7% stated they did not intend to get vaccinated ^[31]C4. Such low coverage leaves a large proportion of the population susceptible to HPV-related cancers, undermining the potential for herd immunity against oncogenic strains.

Disparities in Vaccine-Preventable Disease Burden

The consequences of hesitancy are not evenly distributed. In Sweden, the association between vaccine acceptance and uptake was weaker among individuals born in non-Western countries, suggesting that even when attitudes are favorable, structural barriers or mistrust may prevent vaccination ^[10]C4. In Ecuador, HPV vaccine uptake has fluctuated since its introduction, and the country has one of the highest cervical cancer mortality rates in Latin America ^[15]D5. Parents cited lack of information and fear of side effects as key barriers, while healthcare providers perceived carelessness among parents, a disconnect that perpetuates low coverage. In sub-Saharan Africa, hesitancy driven by young age, rural location, low education, and mistrust of governments contributes to persistently high child morbidity and mortality from vaccine-preventable diseases ^[20]C4.

Economic and Health System Burden

Outbreaks of vaccine-preventable diseases impose substantial costs on health systems and economies. Although direct economic data from the reviewed studies are limited, the resources required for outbreak response, contact tracing, isolation, emergency vaccination campaigns, far exceed the cost of routine immunization. The COVID-19 pandemic highlighted how vaccine hesitancy can prolong public health emergencies and delay recovery of routine vaccination services ^{[29]B2a[30]D5}. In LMICs, the decline in childhood vaccination during the pandemic threatens to reverse decades of progress in reducing under-five mortality ^{[20]C4[29]B2a}.

Pearl: A 3-5% decline in MMR vaccine uptake can reduce herd immunity below the threshold for measles elimination, making early identification of hesitant parents and targeted catch-up campaigns essential to prevent outbreaks ^[27]B2b.

These consequences underscore the need for reliable measurement of vaccine hesitancy to identify at-risk populations and evaluate interventions. Several validated instruments have been systematically evaluated against established methodological standards, providing clinicians and researchers with evidence-based options for assessment.

Parent Attitudes about Childhood Vaccines (PACV) Scale

The Parent Attitudes about Childhood Vaccines (PACV) scale and its linguistically adapted versions are among the most extensively studied instruments. A systematic review of 40 studies evaluating 31 instruments using the COSMIN guidelines rated the Vietnamese version of the PACV (PACV-Viet) as Category A, recommended for use with sufficient content validity and at least moderate evidence for internal consistency ^[28]C4. The original PACV, developed in English, has been translated into multiple languages, though only the Vietnamese version achieved Category A in this analysis. The PACV typically assesses three domains: behavior, safety and efficacy concerns, and general attitudes, with items generating a 0-100 hesitancy score.

Vaccine Hesitancy Scale (VHS)

The Vaccine Hesitancy Scale (VHS), developed by the World Health Organization Strategic Advisory Group of Experts (SAGE), is a widely used generic measure. Strong discriminant validity has been demonstrated in a case-control study of childhood vaccine refusal in Konya, Türkiye: parents who refused vaccines had a mean VHS score of 22.2 ± 6.4 compared with 39.8 ± 6.5 among acceptors (p < 0.001) ^[37]B3b. The VHS comprises 5-10 items covering lack of confidence, risks, and concerns about vaccines. However, the COSMIN review placed the general VHS in Category B, meaning it is recommended but with caution due to some limitations in measurement properties ^[28]C4. Given its brevity and international use, the VHS remains a practical choice for large-scale surveys.

Other Validated Instruments

The COSMIN-based systematic review identified three instruments with Category A recommendation: the Malay version of the modified vaccine hesitancy scale (MVHS-M), the PACV-Viet, and the parental attitude scale towards vaccination (PASV) ^[28]C4. These tools demonstrated sufficient content validity and at least moderate evidence for internal consistency, making them the most robust options for assessing parental vaccine hesitancy. The general vaccine hesitancy scale (GVHS), vaccination attitudes examination (VAX), vaccine acceptance instrument (VAI), and vaccine barriers assessment tool (VBAT) received Category C recommendation (not recommended due to insufficient or inconsistent evidence) ^[28]C4. The remaining 24 instruments fell into Category B.

Selecting a Tool for Clinical or Research Use

Choice of instrument depends on the target population, setting, and purpose. For clinical screening in primary care, a brief tool such as the VHS (5-10 items) may be practical, while research contexts may favor the more comprehensive PACV or PASV. The COSMIN grading provides a benchmark: Category A instruments are preferred when available in the relevant language. The MVHS-M, PACV-Viet, and PASV currently represent the gold standard for parental assessment. However, no single instrument is universally validated across all populations; cultural adaptation and re-validation are essential before use in new settings. The systematic review also highlighted gaps in assessing measurement error and responsiveness, indicating that even recommended instruments require further evaluation ^[28]C4.

Pearl: When selecting a vaccine hesitancy instrument, prioritize tools with Category A COSMIN grading (MVHS-M, PACV-Viet, PASV) for parental assessment; for rapid screening in diverse populations, the VHS provides good discriminant validity but requires cautious interpretation.

Measurement tools identify who is hesitant; communication strategies determine whether that hesitancy resolves or hardens. The evidence base now spans direct patient counseling, provider training, digital outreach, and financial incentives, each with distinct effect sizes and caveats.

The Presumptive Approach and Provider Recommendation

A strong, unambiguous provider recommendation remains one of the most potent levers for vaccine uptake, yet many clinicians hesitate to deliver it. Professional socialization may paradoxically suppress personal hesitancy among healthcare workers while reducing empathy for hesitant patients, creating a communication gap ^[9]C4. Training programs must therefore address not only skills but also the emotional responses, frustration, hopelessness, that clinicians bring to these conversations ^[9]C4. Systematic reviews identify communication skills as a key determinant of vaccine hesitancy among healthcare professionals, alongside knowledge gaps and organizational barriers ^[44]B2a. The presumptive approach ("We need to get your flu shot today") frames vaccination as the default and has been widely endorsed, though its comparative effectiveness against participatory styles in controlled trials remains incompletely quantified.

Motivational Interviewing: Evidence and Application

Motivational interviewing (MI) has the strongest trial support for direct patient counseling. In a randomized controlled trial among 733 postpartum mothers in France, a single MI session delivered by trained midwives reduced vaccine hesitancy scores by 10.1/100 points and increased vaccination intention by 0.8/10 points at seven months, with consistent effects across financial situations ^[41]A1b. This sustained impact contrasts with a cluster-randomized trial of MI-informed provider training across 10 Veterans Health Administration facilities, which found no significant improvement in COVID-19 vaccine uptake (adjusted odds ratio 1.16, 95% CI 0.89-1.50, p = 0.28) or influenza vaccination ^[39]A1b. The discrepancy likely reflects the difference between direct MI counseling (effective) and training clinicians to use MI in routine visits (insufficient without ongoing facilitation). Digital adaptations of MI, such as tailored SMS programs for African American and Latino populations, are under investigation ^[5]D5.

Digital and Social Media Communication Strategies

Social media campaigns show limited and conditional effects. A meta-analysis of 28 randomized trials found that social media-based interventions improved vaccine-related attitudes, knowledge, and intention (standardized mean difference 0.21, 95% CI 0.09-0.34) and reduced hesitancy (risk ratio 0.27, 95% CI 0.19-0.38), but did not significantly increase actual vaccination uptake (risk ratio 1.04, 95% CI 0.96-1.14) ^[43]A1a. A three-arm Instagram trial among 301 adolescents in Italy revealed a critical nuance: an information-based page reduced vaccine hesitancy by 6.9% in students with low information avoidance but increased hesitancy by 8.9% (p = 0.002) in those with high information avoidance ^[38]A1b. This backfire effect underscores the need for personalized, bias-aware content rather than one-size-fits-all messaging.

Addressing Misinformation and Health Literacy

Exposure to health misinformation on social media is common, pooled prevalence 59% (95% CI 44-73%) across eight studies, though heterogeneity is extreme (I² = 99.8%) ^[42]B2a. Younger age, lower health or digital literacy, and minority ethnicity are recurrent risk factors for higher exposure ^[42]B2a. Health literacy itself is a modifiable target: in a Japanese cohort of 6601 vaccinated adults, higher communicative and critical health literacy was associated with lower COVID-19 booster hesitancy (adjusted odds ratio 0.85, 95%), and using more than three diverse information sources further reduced hesitancy (adjusted odds ratio 0.70, 95%) ^[45]B2b. Clinicians should therefore assess patients' information sources and literacy levels, and proactively direct them to reliable, diverse channels.

Financial Incentives as an Adjunct

While not a communication strategy per se, financial incentives can complement counseling. A three-arm trial of 69,972 adults overdue for influenza vaccination found that a $50 incentive plus reminder message nearly doubled the one-week vaccination rate (from 0.343% to 0.613%, p < 0.001), with persistence at 30 days (1.55% to 1.92%, p = 0.002); reminder messages alone had no effect ^[40]A1b. This suggests that incentives remain effective even in a skeptical post-pandemic environment, particularly for patients who have resisted prior outreach.

Tailoring to Readiness and Audience Segmentation

Effective communication requires matching the strategy to the patient's stage of change. Audience segmentation based on vaccine readiness, as employed in the Michigan SMS trial ^[5]D5, allows messages to address specific barriers (e.g., safety concerns, access, mistrust). For patients with high information avoidance, bias-aware content that acknowledges cognitive biases may prevent backfire ^[38]A1b. For those with low health literacy, simple, actionable language and diverse information sources are key ^[45]B2b.

Pearl: Motivational interviewing delivered directly by a trained counselor reduces vaccine hesitancy by approximately 10 points on a 100-point scale and sustains the effect for at least seven months ^[41]A1b; however, training clinicians to use MI in brief visits does not reliably improve uptake ^[39]A1b, the mode of delivery matters as much as the technique.

While effective communication at the point of care is essential, many interventions require broader structural and policy-level approaches to address vaccine hesitancy at scale. Systematic reviews consistently show that multicomponent strategies, combining education, reminders, and community outreach, are more effective than single-component efforts ^{[48]B2a[49]B2a}. The effectiveness of any intervention depends heavily on tailoring to the specific population, local context, and the dominant drivers of hesitancy ^[48]B2a.

Digital and Social Media Interventions

Social media platforms offer wide reach, but their effect on actual vaccination uptake is limited. A meta-analysis of 28 RCTs found that social media-based interventions did not significantly increase vaccination uptake (RR 1.04, 95% CI 0.96-1.14; I² = 66.2%; NNT not calculable from reported data) ^[43]A1a. However, they did produce small but significant improvements in attitudes, knowledge, intention, and confidence (SMD 0.21, 95% CI 0.09-0.34) and reduced hesitancy, resistance, and misinformation (RR 0.27, 95% CI 0.19-0.38; NNT not calculable) ^[43]A1a. These interventions can backfire: in a school-based RCT, an Instagram information page decreased HPV vaccine hesitancy by -6.9% in low-information-avoidance students but increased it by +8.9% in those with high information avoidance ^[38]A1b. Video-based educational interventions similarly improved threat perceptions and awareness (d = 0.17-0.21) but did not change actual vaccination willingness, even in high-risk groups ^[46]A1b. Digital interventions yield heterogeneous results and are best used as part of a broader strategy, not as standalone tools ^[48]B2a.

School-Based Interventions

Schools provide a structured setting to reach children and adolescents during formative years. A meta-analysis of 38 studies (9 RCTs) found that school-based health education significantly improved HPV vaccine knowledge and, in randomized trials, increased HPV vaccine uptake (RR 4.18), though heterogeneity was high and methodological quality varied ^[51]A1a. Effects on attitudes and intention were less consistent ^[51]A1a. Interventions that include interactive components and are sustained over time appear more effective than single-session programs ^[49]B2a.

Healthcare System and Policy Approaches

Institutional factors shape vaccine access at the system level. A Canadian scoping review identified six barriers, inconsistent supply, funding gaps, geographic constraints, regulatory prioritization, vaccine hesitancy, and information inequities, and four facilitators: expanded vaccinator scope of practice, technological advances, targeted initiatives, and inter-institutional collaboration ^[47]D5. Reminder and recall systems are among the most consistently effective interventions, particularly when combined with patient education ^[48]B2a. Legislative measures, such as school-entry vaccination mandates, have shown effectiveness in increasing coverage but require careful ethical and legal consideration (see Section 10) ^[48]B2a. Financial incentives have been used but are less well-studied in the context of hesitancy reduction; the evidence is insufficient to recommend them as a primary strategy ^[48]B2a.

Community Engagement and Culturally Targeted Interventions

Interventions that engage trusted community leaders and are culturally tailored consistently outperform generic approaches. A systematic review of interventions for ethnic minority populations found that multicomponent, tailored strategies delivered by healthcare workers, including staff training and prompts/cues, were associated with positive effects, though no single strategy emerged as superior ^[52]B2a. In South Asia, lack of awareness, cultural taboos, religious beliefs, and fear of side effects drive HPV vaccine hesitancy, necessitating community-level awareness campaigns and culturally relevant health education ^[22]C4. In sub-Saharan Africa, low educational attainment, rural location, safety doubts, and mistrust of government are key barriers, reinforcing the need for context-specific, trust-centered approaches ^[20]C4. Trust in the healthcare system is the strongest predictor of vaccine uptake, as demonstrated by machine learning analysis of survey data from Alaska ^[12]C4.

Limitations and Future Directions

Despite the evidence supporting multicomponent and tailored interventions, many studies are non-randomized, have high risk of bias, and lack long-term follow-up ^{[48]B2a[50]B2a}. The heterogeneity in outcome measures and intervention designs makes meta-analysis difficult for many strategies ^{[49]B2a[50]B2a}. Future research should standardize methods, assess long-term impact, and evaluate practical implementation, especially in low-income settings where the burden of vaccine-preventable disease is highest ^[50]B2a.

Pearl: When designing interventions, remember that trust is the strongest predictor of vaccine uptake ^[12]C4 and that social media campaigns can paradoxically increase hesitancy in high-information-avoidance groups ^[38]A1b; therefore, always pair digital outreach with community engagement and system-level support.

Policy interventions provide a framework, but vaccine hesitancy manifests differently across populations, requiring tailored strategies that address the specific drivers of each group.

Pediatrics

Parental hesitancy remains the dominant barrier to childhood immunization. A European systematic review identified trust in healthcare professionals as the key factor, with fear of side effects, logistical barriers, and low perceived disease risk contributing negatively ^[18]C4. Among 31 instruments evaluated using COSMIN guidelines, the Malay version of the modified vaccine hesitancy scale (MVHS-M), the Vietnamese version of the Parent Attitudes About Childhood Vaccines survey (PACV-Viet), and the Parental Attitude Scale Towards Vaccination (PASV) received Category A recommendations for assessing parental hesitancy ^[28]C4. Paternal attitudes are particularly influential: a Saudi Arabian review found higher hesitancy among fathers regarding safety, novelty, and long-term effects, associated with delayed schedules and reduced uptake of optional vaccines ^[55]C4. In the COVID-19 context, one in five parents expressed skepticism about pediatric vaccination, with safety and trust concerns universal across all 22 studies reviewed ^[53]C4. HPV vaccine hesitancy in South Asia is driven by lack of awareness, cultural taboos, and inadequate healthcare recommendations ^[22]C4. Interventions targeting parental hesitancy include narrative-based, web-based, and culturally-tailored approaches, but effectiveness varies considerably ^[49]B2a.

Pregnancy

Pregnant women face unique vaccine-related concerns, particularly regarding Tdap and influenza vaccines. Digital and social media campaigns have effectively reduced hesitancy and enhanced trust among hesitant pregnant women in the United States ^[32]B2a. Safety concerns during pregnancy, perceived lack of evidence, and fear of adverse effects are common. The general drivers of hesitancy, trust in healthcare providers, convenience, and complacency, apply, but pregnancy-specific risk perception is critical. Tailored communication that addresses fetal safety and provides clear evidence from pregnancy registries can improve uptake.

Elderly

Fewer studies have examined vaccine hesitancy specifically among older adults, but available data suggest that age modulates responsiveness to communication strategies. In one analysis, adults aged 25-34 years were more responsive to a social media campaign, but patterns in older age groups remain less characterized ^[32]B2a. Elderly populations often have higher perceived risk of disease, which may reduce complacency, but they also face barriers such as limited access, comorbidities, and concerns about vaccine interactions with medications. Given the high burden of influenza and pneumococcal disease in this group, tailored outreach emphasizing concrete benefits and safety in the context of polypharmacy is warranted.

Immunocompromised

Children and adults with chronic medical conditions represent a particularly vulnerable group. Among parents of children with previous medical conditions, 31.8% expressed concerns about COVID-19 vaccination, reflecting heightened risk perception and safety worries ^[53]C4. Immunocompromised individuals may also have lower confidence in vaccine efficacy due to reduced immune responses, and may fear that vaccination could trigger disease flares. Healthcare providers should proactively address these concerns with evidence on vaccine safety and efficacy in immunosuppressed populations, and consider shared decision-making.

Healthcare Workers and Ethnic Minority Communities

Healthcare workers (HCWs) themselves are a key population for vaccine uptake, yet global HBV vaccination coverage among nurses is only 44.8%, with coverage lower in low- and middle-income countries (39.3%) and Africa (27.5%) ^[54]C4. Barriers are primarily structural, vaccine unavailability (33.8%) and financial costs (24.4%), rather than attitudinal hesitancy ^[54]C4. Interventions targeting HCWs to promote vaccine uptake in ethnic minority populations have used persuasion, enablement, and education; effective strategies included multi-component, tailored approaches with staff training and prompts/cues, but no single strategy proved superior ^[52]B2a. Ethnic minority populations often face historical mistrust, exposure to misinformation, and cultural barriers. Misinformation exposure on social media is higher among younger age, lower health literacy, and minority ethnicity ^[42]B2a. Religiosity (b=0.17) and cultural congruence (OR 1.89) significantly influence message credibility and engagement ^[32]B2a. Tailored, culturally congruent communication delivered by trusted HCWs is essential.

Pearl: When addressing vaccine hesitancy in special populations, use validated instruments (e.g., PACV-Viet, MVHS-M) to identify specific concerns, then tailor interventions, such as narrative-based education for parents, digital campaigns for pregnant women, and culturally congruent messaging for ethnic minorities, to the unique drivers of each group ^{[28]C4[32]B2a[52]B2a}.

The preceding section on special populations highlighted groups with unique hesitancy patterns; the COVID-19 pandemic amplified these dynamics globally, introducing unprecedented challenges that reshaped vaccine acceptance. The pandemic compressed vaccine development timelines, accelerated novel platforms such as mRNA vaccine|mRNA and viral vectors, and exposed populations to an "infodemic" of misinformation, all of which created a distinct landscape for vaccine hesitancy ^[30]D5.

Prevalence and Patterns of COVID-19 Vaccine Hesitancy

COVID-19 vaccine hesitancy varied widely across populations and settings. Among people with epilepsy, a meta-analysis of 14 studies (n=4230) found overall vaccination willingness of 51.7%, with 44.2% of unvaccinated individuals expressing willingness ^[34]B2a. Well-controlled epilepsy was associated with higher vaccination rates (OR 1.91), while frequent seizures reduced likelihood (OR 0.52) ^[34]B2a. In pediatrics, a systematic review reported that one in five parents was skeptical about COVID-19 vaccination for their children, with safety and trust concerns present in 100% of included studies ^[53]C4. In low- and middle-income countries (LMICs), the pandemic had a predominantly negative or neutral effect on attitudes toward non-COVID-19 vaccines, with 91% of studies reporting changes in "Thinking and Feeling" constructs ^[29]B2a. Socio-demographic factors, young age, rural location, low educational attainment, were major determinants of COVID-19 vaccine refusal, while childhood vaccine refusal was more driven by information and cognitive factors ^[58]D5.

Drivers: Misinformation, Rapid Development, and Distrust

The rapid development and emergency use authorization of COVID-19 vaccines fueled concerns about safety and efficacy, which were amplified by social media and political polarization. A systematic review of media exposure found that digital and social media campaigns could reduce hesitancy, but negative reportage through social media platforms created mistrust in vaccine intentions ^{[32]B2a[56]D5}. In sub-Saharan Africa, doubts about safety and efficacy, fear of side effects, and mistrust of governments were key barriers ^[20]C4. The Health Belief Model meta-analysis (77 studies, n=83,995) identified perceived benefits (r=0.40) as the strongest positive predictor of acceptance, while perceived barriers (r=-0.25) were the strongest negative predictor ^[57]C4. Among individuals with epilepsy, fear of seizure worsening (23.8-88.5% across studies) and side effect concerns (13.0-53.0%) were primary reasons for hesitancy ^[34]B2a. Differences by region of birth emerged: in Sweden, trust in vaccines (OR 2.5 for Swedish-born; OR 1.6 for non-Western-born) and benefit-risk balance (OR 1.7 for non-Western-born) were significant, but descriptive norms were not associated with uptake in non-Western groups ^[10]C4.

Interventions and Lessons Learned

Interventions to address COVID-19 vaccine hesitancy had mixed success. A video-based educational intervention for individuals with mental disorders (n=639) improved awareness of vaccination importance (d=0.17, p=0.033) and perceived severity (d=0.21, p=0.010) but did not significantly increase vaccination willingness ^[46]A1b. A cluster-randomized trial of motivational interviewing (MI)-informed provider education across 10 VA facilities (n=338,718 veterans) found no significant difference in COVID-19 vaccine uptake (aOR 1.16, 95% CI 0.89-1.50) ^[39]A1b. However, tailored communication strategies delivered via radio, web platforms, and social media significantly improved acceptance in experimental studies: adaptive campaigns achieved up to an 8% weekly increase in uptake in Madagascar (RR 1.08) and a 7.8% higher vaccination rate among Nigerian adults ^[32]B2a. For parental hesitancy, recommended strategies include tailored education programs, streamlining distribution, engaging local community opinion leaders, and appropriate risk communication by public health institutions ^[53]C4. In Ghana, a community-based approach with multi-stakeholder engagement was proposed to address health system barriers such as untimely payment of vaccinators, logistics shortfalls, and long queues ^[56]D5. The post-COVID-19 era demands that future vaccine strategies be not only scientifically robust but also globally inclusive and implementation-ready, with continuous alignment between scientific progress and equitable access ^[30]D5.

Pearl: The strongest predictor of COVID-19 vaccine acceptance is perceived benefit (r=0.40), while perceived barriers (r=-0.25) are the strongest deterrent; interventions that address specific concerns (e.g., seizure worsening in epilepsy, safety in parents) and leverage trusted local communicators are more effective than generic educational campaigns ^{[57]C4[34]B2a[53]C4}.

The COVID-19 pandemic amplified long-standing ethical tensions between individual autonomy and collective public health protection, forcing a re-examination of the legal grounds for vaccine mandates, exemptions, and consent ^[59]C4[61]D5. The requirement of a "green pass" for international travel, for example, raised fundamental questions about the legitimacy of linking vaccination status to fundamental freedoms, particularly in sub-Saharan Africa where acceptance rates were only 54.73% (95% CI 50.54%-58.89%) ^[59]C4. These debates are not new: parental refusal of routine childhood vaccination has generated a rich normative literature spanning principlism, parental rights, children's best interests, and the public health duty to prevent harm to others ^[61]D5.

Ethical Frameworks: Autonomy, Beneficence, and Justice

Two central ethical questions dominate the literature: (1) whether vaccine refusal is justifiable, and (2) whether strategies for dealing with those who refuse are justifiable ^[61]D5. Arguments for refusal rely on principlism, religious frameworks, parental rights, and the medico-legal best interests of the child standard; arguments against refusal emphasize the potential to cause harm to others and the rights of children to be protected from preventable disease ^[61]D5. The principle of justice demands that vaccine mandates do not disproportionately burden already marginalized populations. Migrant populations in Europe, for instance, experience vaccine hesitancy shaped by institutional mistrust, limited health literacy, and informal information networks, factors that are amplified by structural vulnerabilities rather than by autonomous choice alone ^[60]C4.

Legal Frameworks: Mandates, Passports, and Exemptions

Legal responses to vaccine hesitancy vary widely. Non-medical exemptions (conscientious or religious) are permitted in many jurisdictions but remain ethically contested; the normative literature questions whether such exemptions are sustainable when herd immunity is threatened ^[61]D5. In the United States, pediatric vaccinations are deeply politicized, and autonomy-confirming messages, which affirm a parent's right to decide rather than an authoritarian tone, have been shown to increase vaccine confidence and intention to vaccinate among conservative parents, a group often resistant to mandates ^[63]A1b. When legal measures are considered, the main policy concern is whether enforcement is legal and to what extent it is justified ^[64]C4. Clinicians must be aware that the legal precedent for vaccinating children against a parent's will exists primarily in the American and UK settings, typically justified by the best-interests standard ^[61]D5.

Informed Consent and Autonomy-Affirming Communication

Respect for autonomy requires that vaccination decisions be made with adequate information, free from coercion, but it does not require passivity from clinicians. Autonomy-affirming communication, messaging that acknowledges the parent's authority and avoids shaming, has been shown to increase vaccine confidence, especially among parents with conservative political leanings ^[63]A1b. In contrast, authoritarian approaches risk exacerbating distrust and entrenching refusal. Among pregnant women in Iran, fear of vaccine side effects on the fetus was the most common reason for refusal (86.5%), and 86.5% still refused after advice from medical staff, underscoring the limits of information provision alone when deep-seated beliefs about fetal safety are not addressed ^[66]C4. The ethical obligation of clinicians is to provide transparent, empathetic counseling that respects the patient's values while presenting the evidence clearly.

Ethical Guidance for Clinicians

Physicians face a spectrum of ethical choices, from nudging toward vaccination to dismissing patients who refuse. The literature supports a graduated approach: start with autonomy-affirming dialogue, escalate to motivational interviewing, and only consider dismissal or legal action when the child is at imminent risk of serious harm ^[61]D5. The least restrictive alternative that achieves the public health goal should be favored. Mandatory vaccination programs must be transparent, evidence-based, and applied equitably, with exemptions granted only where genuinely justified by medical contraindications or deeply held religious beliefs ^[61]D5.

Pearl: The ethical obligation to respect patient autonomy does not preclude the use of evidence-based communication strategies that affirm parental decision-making authority while promoting vaccination, autonomy-confirming messages have been shown to increase vaccine confidence among hesitant parents, particularly those with conservative political beliefs, and should be the first-line approach before considering mandates or dismissal ^[63]A1b.

Despite a decade of intensified study, the evidence base for vaccine hesitancy interventions remains thin at critical points. The preceding ethical and legal frameworks highlight the need for fair, respectful approaches, but translating those principles into robust, scalable strategies requires filling several empirical gaps.

Gaps in Understanding Long-Term Hesitancy Trajectories

Most studies capture hesitancy at a single time point or shortly after an intervention. Little is known about the natural history of hesitancy, whether it remits, solidifies, or cycles over years, especially for vaccines that require multiple doses or boosters ^[68]D5. The COVID-19 pandemic demonstrated that willingness can shift rapidly with new variants, policy changes, or media events, yet longitudinal data on these dynamics remain scarce ^[1]D5. Systematic review evidence from Europe identifies health engagement and social media exposure as emerging determinants, but how these factors interact over time is poorly characterized ^[68]D5.

Effectiveness of Digital and Theory-Based Interventions

Digital tools, SMS reminders, mobile apps, chatbots, and web-based platforms, have shown promise, particularly for HPV vaccination, where SMS-based interventions consistently increased uptake ^[69]D5. However, a recent randomized controlled trial testing attitudinal inoculation and cognitive behavioral therapy (CBT) kernel messaging against standard public health messaging found that COVID-19 vaccination uptake at 4 weeks was only 1.2% overall (95% CI 0.6%-1.8%), with no significant difference between arms (CBT kernel vs standard: risk difference 0.3%, 95% CI -1.3% to 1.8%) ^[67]A1b. This underscores that even theory-informed messages may fail to overcome deeper barriers. Future research must identify which components of digital interventions, tailoring, motivational interviewing, cultural adaptation, actually drive action, and under what conditions ^[5]D5[69]D5.

Need for Standardized Measurement and Rigorous Study Designs

Current evidence is fragmented by heterogeneous definitions, outcome measures, and study populations. The overview of systematic reviews in Europe found that only 88 reviews met inclusion criteria, and many relied on low-quality designs ^[68]D5. A core outcome set for vaccine hesitancy research, analogous to those in other fields, would enable meta-analysis and comparison across settings. Rigorous designs, including pragmatic trials, stepped-wedge cluster designs, and nested qualitative studies, are needed to evaluate real-world effectiveness, not just efficacy in controlled conditions ^[68]D5[30]D5.

Emerging Challenges: New Vaccines, Post-COVID Context, and Equity

Novel TB vaccines for adolescents and adults are approaching licensure, but hesitancy determinants, particularly vaccine novelty, media environment, and safety concerns, will pose adoption barriers, as shown in UK qualitative evidence ^[1]D5. The post-COVID era has accelerated platform technologies (mRNA, viral vectors) but also amplified misinformation and eroded trust in some communities ^[30]D5. Future strategies must prioritize global equity, ensuring that digital and community-based interventions are culturally tailored and accessible to marginalized populations, including those with limited digital literacy or internet access ^[69]D5[30]D5.

Pearl: The failure of theory-enhanced messaging to meaningfully increase uptake in recent trials, with overall COVID-19 vaccine uptake of just 1.2% at 4 weeks, underscores that future interventions must move beyond information-deficit models and address structural, emotional, and contextual barriers ^[67]A1b.