Trends and disparities in HPV vaccination among U.S. adolescents, 2018–2023

1.1 Theoretical framework: Optimal vaccination coverage and herd immunity thresholds

The concept of herd immunity provides the theoretical foundation for understanding optimal vaccination rates in populations. The herd immunity threshold is mathematically defined as ( h c = 1 − R 0 ) where R 0 represents how easily the virus spreads [9]. For HPV, studies suggest that at least 70–90% coverage is needed to stop the virus from spreading widely [10,11]. The theoretical importance of achieving high vaccination coverage has become increasingly urgent as the epidemiologic landscape of HPV-related cancers has fundamentally shifted. Oropharyngeal cancers, predominantly affecting men, now surpass cervical cancer as the most common HPV-associated malignancy in the United States, with incidence rates continuing to rise despite the availability of effective vaccines [12]. This epidemiologic transition emphasizes the critical importance of achieving gender-neutral vaccination coverage at levels sufficient for population-level protection.

1.2 Lessons from COVID-19: Vaccination program resilience and coverage thresholds

The COVID-19 pandemic provided an unprecedented natural experiment in vaccination program implementation and revealed critical insights about achieving optimal coverage rates under real-world conditions. Studies suggested that 60–70% population coverage would achieve herd immunity for SARS-CoV-2, with some estimates reaching 90% for highly transmissible variants [13–15]. However, practical experience demonstrated significant gaps between theoretical thresholds and achievable coverage rates, with most high-income countries reaching a practical ceiling of approximately 75–80% vaccination coverage despite resource mobilization [16].

The pandemic experience revealed several critical lessons relevant to HPV vaccination programs. First, achieving high vaccination coverage requires more than mathematical modeling of herd immunity thresholds; it demands robust delivery systems, sustained community engagement, adaptive program design, and crisis-resilient infrastructure capable of maintaining services during public health emergencies [17,18]. Second, vaccination programs are particularly vulnerable to disruptions that compound existing health disparities, with rural communities, racial and ethnic minorities, and socioeconomically disadvantaged populations experiencing disproportionate barriers to vaccine access [19,20]. These lessons reveal the importance of understanding how vaccination programs perform under stress and which populations are most vulnerable to coverage disruptions during public health emergencies.

1.3 Literature gap and study rationale

While extensive research has documented HPV vaccination disparities and coverage trends, a critical gap remains in understanding how coverage evolved before, during, and after the COVID-19 crisis. Most existing studies rely on cross-sectional, single-year data, or focus on limited geographic areas, limiting insight into long-term national trends and program resilience during major public health disruptions [21–23]. Although previous research confirms that COVID-19 significantly disrupted routine childhood vaccinations globally [24], HPV-specific coverage patterns across distinct pandemic phases remain insufficiently explored.

This knowledge gap is particularly important given the unique characteristics of HPV vaccination programs. Unlike routine childhood vaccines administered in early infancy, HPV vaccines are delivered to adolescents who may have delayed or missed healthcare visits during pandemic-related disruptions [24]. Additionally, HPV vaccination often requires multiple healthcare encounters and faces distinctive challenges related to vaccine hesitancy and parental decision-making that may have been worsened during the pandemic [25,26].

Furthermore, the timing of the first national decline in U.S. HPV vaccination rates in nearly a decade occurred during this period [3], yet no comprehensive analysis has examined how this decline varied across demographic and geographic populations, or what these patterns reveal about strategies for achieving optimal vaccination coverage during normal and crisis conditions.

Understanding these patterns is essential for three critical reasons. First, they inform targeted strategies to not only recover but improve upon pre-pandemic coverage levels. Second, they reveal structural vulnerabilities that hinder progress toward optimal population protection. Third, they offer guidance for designing vaccination systems resilient enough to sustain herd immunity goals during future public health crises.

1.4 Research questions and study objectives

To address this critical gap in the literature, this study examines HPV vaccination coverage trends from 2018 to 2023, covering the pre-pandemic, pandemic, and post-pandemic periods. This timeframe offers a natural experiment for evaluating how coverage patterns responded to public health system stress and for assessing progress toward herd immunity coverage thresholds.

Specifically, this study addresses three interconnected research questions that bridge theoretical vaccination coverage models with real-world program implementation:

1. Coverage trajectory analysis: How did HPV vaccination coverage change before, during, and after the COVID-19 pandemic? How do these trends compare to the Healthy People 2030 TARGETS for optimal population protection?

2. Disparities in coverage: Which demographic and geographic groups experienced the greatest shifts in vaccination coverage during this period?

3. Path to optimal coverage: What do these observed patterns reveal about program vulnerabilities and strategies needed to achieve sustained, high coverage?

Using provider-verified national surveillance data, this study generates evidence-based recommendations for reaching the 80% national coverage target, strengthening pandemic-resilient vaccination systems, and addressing persistent equity gaps that hinder progress toward HPV-related cancer prevention. Findings will inform both immediate recovery efforts and longer-term strategies aligned with theoretical thresholds for population-level protection.

2.1 Sample and data source

This study used data from the National Immunization Survey–Teen (NIS-Teen), collected annually from 2018 to 2023. The NIS-Teen is a nationally representative surveillance system administered by the Centers for Disease Control and Prevention (CDC) to monitor vaccination coverage among U.S. adolescents aged 13–17 years. Data are collected in two phases. In the first phase, parents or guardians participate in a structured telephone interview that gathers demographic and health information. In the second phase, immunization providers identified during the interview are contacted to verify the adolescent’s vaccination history. Only adolescents with provider-verified HPV vaccination records were included in this analysis to ensure accurate assessment of vaccination status. To evaluate changes in HPV vaccination coverage across the COVID-19 pandemic, the six survey years were divided into three time periods: before the pandemic (2018–2019), during the pandemic (2020–2021), and after the COVID-19 pandemic (2022–2023). We adopted this categorization based on a framework used in recent vaccine coverage study [27], which defined distinct pandemic phases to assess time-specific impacts of public health emergencies on immunization programs. This structure allowed us to track how vaccination rates shifted in response to disruptions in healthcare delivery and public health efforts.

2.2 Measures of variables

The study’s two primary outcomes were HPV vaccine initiation and UTD status. Initiation was defined as receiving at least one dose of the HPV vaccine. UTD status followed CDC guidelines and was defined as receiving either two doses when the first dose was given before age 15 and spaced at least 5 months minus 4 days apart, or three or more doses if the series was initiated at age 15 or older, or if the adolescent was immunocompromised [28].

The main explanatory variables included age (13–17 years), sex (male or female), race and ethnicity (non-Hispanic White, non-Hispanic Black, Hispanic, or non-Hispanic others), and state of residence (based on respondent-reported U.S. state). These variables were chosen based on their relevance to vaccination disparities and their ability to help answer the study’s central questions on temporal trends and subgroup differences.

2.3 Data analysis procedure

All analyses accounted for the complex sampling design of the NIS-Teen using CDC-provided provider-phase weights. These weights correct for unequal probabilities of selection, nonresponse at both household and provider levels, and post-stratification adjustments. Weighted proportions were calculated for HPV vaccine initiation and UTD coverage, stratified by survey year and demographic subgroups.

Trend analysis was performed using the Cochran–Armitage test for trend, which assesses whether changes in vaccination rates over time followed a linear pattern across the three pandemic periods. This method was applied separately for both outcomes. Subgroup trends were examined descriptively; however, this study did not use multivariable regression models, as the primary objective was to identify temporal and spatial patterns rather than estimate causal effects.

All analyses were conducted in R (v4.4.1) using survey-weighted functions, excluding <1% of adolescents with missing primary outcomes data.

2.4 Ethical considerations

This study used publicly available, de-identified data from the NIS-Teen surveillance system. The original data collection was approved by the National Center for Health Statistics Research Ethics Review Board. No additional institutional review board approval was required for this secondary data analysis.

1. Informed consent: Not applicable. This study analyzed de-identified, publicly available data.

2. Ethical approval: Not applicable. The National Immunization Survey–Teen (NIS-Teen) dataset used in this research is publicly available and fully anonymized. No additional ethical approval was required.

4.1 Synthesis of main findings

Table 1.

4.2 Contribution to existing literature

This study provides the first comprehensive national analysis of HPV vaccination trends across the COVID-19 pandemic period, addressing critical knowledge gaps in our understanding of vaccination resilience during public health emergencies. Unlike previous studies that examined single-year snapshots or localized populations [29,30], our findings reveal complex temporal patterns that challenge conventional assumptions about pandemic impacts on routine immunization.

Our results contradict the prevailing narrative that COVID-19 universally disrupted childhood vaccination programs [31–33]. While another study documented drop in HPV vaccine uptake in 2020 [34], our national data show that initiation rates actually increased during the pandemic period, suggesting that the U.S. vaccination system demonstrated remarkable adaptability. The persistence of racial and ethnic disparities in our data confirms patterns identified in pre-pandemic studies, where Hispanic and Black adolescents consistently showed higher vaccination rates than their White counterparts [8,35]. These finding challenges common assumptions about health equity and represents what research has termed “reverse disparities” in HPV vaccination, where racial/ethnic minorities demonstrate higher uptake rates compared to White adolescents [36]. These reverse disparities are unique, as racial and ethnic minorities are generally less likely to receive adolescent preventive services [37], but the HPV vaccination context appears to be an exception to this pattern.

4.3 Expected and unexpected findings

This study confirmed several known trends in HPV vaccination, while also uncovering surprising findings that challenge assumptions. We found that uptake remains lower among White adolescents, a trend mirrored in national surveys showing higher HPV initiation among Hispanic and Black teens compared to non-Hispanic Whites [38,39]. Similarly, the continued sex disparities were expected, reflecting the HPV vaccine’s initial introduction as a cervical cancer prevention tool for females [40]. The narrowing of these gaps over time was expected following the 2011 expansion of recommendations to include males [41], though the persistence of disparities suggests that parent attitudes may lag behind policy changes [42]. These patterns address the research questions from our Introduction about whether demographic differences persist.

Contrary to global trends, we found the U.S. achieved an unexpected improvement in HPV coverage during the COVID-19 pandemic (2020–2021). While studies in Europe and low- to middle-income countries have reported declines in coverage, current levels range between 50% and 65% [43], U.S. rates not only rebounded but surpassed 2019 levels [24]. High-performing regions, specifically the Northeast and Upper Midwest also met expectations, reflecting longstanding strengths in public health infrastructure, provider practices, and overall vaccination uptake [44–46].

The most surprising finding was that HPV vaccination coverage improved during the pandemic period (2020–2021) rather than declining as anticipated. This contradicts the widespread disruption to healthcare services documented globally [32]. Several factors may explain this unexpected trend, including the rapid implementation of telehealth services and modified care delivery models that improved access for some populations. For example, during June–November 2020, approximately 30% of weekly health center visits occurred via telehealth, enabling continued access to care during pandemic disruptions [47]. The pandemic may have also heightened public awareness of vaccine-preventable diseases, which in turn increased acceptance of routine immunizations [48]. Additionally, targeted public health campaigns and catch-up vaccination efforts launched by the CDC and partner agencies played a role in mitigating missed doses and sustaining adolescent vaccination coverage [49]. These actions reflect the U.S. healthcare system’s adaptability and resilience during a national crisis.

Yet, this national resilience masked troubling state-level gaps, nowhere more evident than in Mississippi. Despite federal support and widespread catch-up efforts, Mississippi’s HPV vaccination coverage consistently remained below 60%, making it the worst-performing state in the country. This failure is not incidental; it highlights deeply rooted issues in healthcare access, provider engagement, and community trust [50]. In contrast to high-performing states like Rhode Island, where strong infrastructure and proactive public health strategies drove coverage above 80% [50]. Mississippi’s stagnation suggests that national campaigns alone are insufficient. Addressing such extreme disparities will require tailored, on-the-ground interventions that go beyond broad messaging and confront the specific cultural, political, and structural barriers limiting vaccine uptake in the most vulnerable regions.

Another concern was the decline in UTD HPV vaccination coverage observed in 2023, which disrupted the upward trend established during the pandemic period. Modeling studies have shown that even reductions in vaccination coverage can result in increased incidence of HPV-related cancers over time if left unaddressed [51]. While the long-term effects of this decline remain to be fully seen, the reversal signals that short-term gains in coverage may not be sustainable without continuous public health attention. These findings reinforce the importance of maintaining vaccination infrastructure and targeted interventions, particularly during periods of shifting public health priorities.

4.4 New insights and contributions

This study confirms established disparities in race, sex, and geography while providing critical context. Our findings reveal the U.S. vaccination system’s capacity to maintain HPV vaccination rates during COVID-19, contrasting with global declines in routine immunizations. However, the data also expose the fragility of coverage gains post-pandemic. By linking these patterns to regional HPV prevalence data, we demonstrate how policy responses and healthcare system adaptations directly shape public health outcomes.

4.5 Broader implications

Our results offer important lessons for high-income countries. Adaptive healthcare infrastructure can sustain preventive services during crises, but equity requires deliberate action rather than emerging naturally. Even healthcare systems with universal coverage face persistent disparities rooted in cultural factors, provider practices, and incomplete vaccination series. While other nations can draw insights from the U.S. experience, they should implement protective measures to prevent post-crisis rollbacks in preventive care.

4.6 Policy recommendations

Incentive system theory provides a practical framework for improvement. Federal policy should tie provider incentives to series UTD rather than just initiation, particularly targeting high-risk populations. Research has shown that financial incentives and systematic reminders increase HPV vaccination uptake [52]. Designating HPV vaccination as a national healthcare priority, with routine public reporting of state-level performance metrics, would maintain focus and drive accountability across regions.

Real-time surveillance systems could identify underperforming areas early, enabling rapid deployment of mobile clinics, targeted provider training, and community outreach programs. State and local interventions should address specific barriers through evidence-based approaches like school-based reminder systems and streamlined consent processes, particularly in communities with low completion rates.

Healthcare systems should implement comprehensive reminder systems through electronic health records, automatic appointment scheduling, and consent tracking to reduce follow-up gaps. Provider communication represents an equally critical component. Training programs in narrative education and motivational interviewing can address persistent vaccine hesitancy and clearly communicate benefits to families. Integrating these practices into annual quality improvement cycles ensures sustained implementation and continuous refinement.

5.1 Theoretical implications

Our findings fundamentally challenge existing theoretical frameworks about healthcare system vulnerability during public health emergencies. Traditional disaster preparedness models predict uniform degradation of non-essential services during crises, yet our data demonstrate what we term “selective resilience” – the capacity for well-supported preventive services to maintain or even improve performance while other healthcare components face significant disruption. This concept extends beyond simple system robustness to encompass adaptive capacity that can leverage crisis conditions to accelerate existing improvement trends.

The persistence of racial and ethnic disparities during a period of overall coverage improvement reveals critical theoretical insights about the relationship between system-level performance and health equity. Our results suggest that healthcare infrastructure resilience and population-level equity operate through fundamentally different mechanisms, requiring distinct theoretical frameworks. These findings challenge health services research assumptions that system improvements automatically benefit all populations equally, instead supporting theories of “differential access” where structural advantages and disadvantages are maintained or even amplified during periods of change.

The emergence and persistence of “reverse disparities” in HPV vaccination – where racial and ethnic minorities demonstrate higher uptake than White adolescents – represents a unique phenomenon in public health that deserves greater theoretical attention. This pattern contradicts standard minority health frameworks and suggests that vaccine-specific factors, historical public health messaging, and community trust dynamics create distinct pathways for health behavior adoption that may not generalize to other preventive services.

Our temporal analysis also contributes to implementation science theory by demonstrating how external shocks can create windows of opportunity for accelerating existing public health initiatives. The pandemic period’s improved HPV vaccination rates suggest that crisis conditions can enhance system adaptability and community receptiveness to preventive interventions when supported by appropriate infrastructure and messaging.

5.2 Managerial and policy implications

Healthcare administrators and policymakers can derive several actionable insights from our findings that extend beyond HPV vaccination to broader preventive care delivery. First, investment in robust preventive care infrastructure – including electronic health record systems, automated reminder protocols, telehealth capabilities, and provider training programs – provides returns that extend beyond normal operations by creating system resilience during emergencies. Healthcare organizations should conceptualize these elements as essential components of emergency preparedness rather than merely quality improvement initiatives.

Second, our results demonstrate that maintaining aggregate population-level performance metrics is insufficient for achieving health equity goals. The persistence of state-level disparities, exemplified by Mississippi’s consistently poor performance despite national improvements, reveals the limitations of broad-based policy approaches. Policymakers must implement active monitoring systems that track disparities in real-time and deploy targeted interventions when geographic or demographic gaps persist or widen. This requires fundamental shifts from population-level performance metrics to equity-focused accountability measures that incentivize providers and health systems to address disparities proactively.

The post-pandemic decline in UTD coverage observed in 2023 highlights the critical importance of sustained attention to preventive services. Policymakers should develop mechanisms to maintain focus on routine immunizations even when public health priorities shift toward emerging threats. This could include establishing dedicated funding streams for preventive services that are protected from reallocation during crisis periods, or implementing automatic triggers that deploy additional resources when coverage rates decline.

For provider-level interventions, our findings support transitioning from initiation-focused metrics to UTD -focused accountability measures. The persistent gap between initiation and UTD coverage across all demographic groups suggests that current systems successfully engage families initially but fail to support series completion. Healthcare systems should implement comprehensive tracking mechanisms that monitor patients throughout the vaccination series and deploy targeted interventions when follow-up appointments are missed.

International policymakers can learn from both the successes and limitations of the U.S. experience. While strong healthcare infrastructure enabled resilience during the pandemic, the persistence of geographic and demographic disparities reveals that infrastructure alone is insufficient. Countries developing HPV vaccination programs should prioritize building equitable delivery systems from the outset rather than attempting to address disparities after achieving high aggregate coverage rates.

5.3 Ideas for future research

Several critical research directions emerge from our findings that could significantly advance understanding of preventive care delivery, health equity, and pandemic preparedness. First, mixed-methods longitudinal studies following individual patients and families through the pandemic period could illuminate decision-making processes that aggregate surveillance data cannot capture. Such research should examine how pandemic experiences shaped attitudes toward preventive care, whether families who delayed care eventually caught up, and how provider communication strategies evolved during different phases of the crisis.

Second, comparative international research examining HPV vaccination patterns during COVID-19 across different healthcare systems could test the generalizability of our findings about selective resilience. Cross-national studies could identify specific system characteristics that promote equitable preventive care delivery during emergencies and inform policy transfer efforts between countries with different organizational and financing structures. Such research should particularly focus on countries that maintained both high coverage and low disparities during the pandemic to identify best practices.

Third, implementation science research should examine the specific organizational adaptations that enabled some healthcare systems to maintain or improve HPV vaccination delivery during the pandemic. Case studies of high-performing health systems, states, and individual practices could identify transferable strategies for maintaining equity-focused preventive care during emergencies. This research should investigate how successful organizations modified workflows, communication strategies, and performance monitoring systems to sustain vaccination services.

Fourth, behavioral economics research could explore how crisis conditions alter decision-making around preventive health behaviors. The unexpected improvement in HPV vaccination rates during 2020–2021 suggests that pandemic conditions may have created unique psychological or social dynamics that enhanced vaccine acceptance. Understanding these mechanisms could inform strategies for promoting preventive behaviors during future emergencies or even during normal circumstances.

Fifth, health disparities research should investigate the mechanisms underlying “reverse disparities” in HPV vaccination and whether similar patterns exist for other preventive services. Such studies could examine how historical public health messaging, community trust dynamics, and provider practices interact to create differential uptake patterns across racial and ethnic groups. This research could inform more effective communication strategies and help predict which populations might be most responsive to specific intervention approaches.

Finally, health economics research should evaluate the cost-effectiveness of different strategies for maintaining preventive services during public health emergencies. Our findings suggest that infrastructure investments enabling pandemic resilience may provide substantial returns, but quantitative analyses are needed to guide resource allocation decisions. Such studies should examine both the direct costs of maintaining services and the long-term health and economic consequences of coverage disruptions.

These research directions collectively could inform the development of more resilient, equitable, and effective preventive care systems capable of maintaining high-quality services regardless of external circumstances while actively addressing persistent health disparities. The COVID-19 pandemic provided a good experiment in healthcare system adaptation that researchers should continue to mine for insights applicable to future public health challenges.