A systematic literature review of human papillomavirus vaccination strategies in delivery systems within national and regional immunization programs

ABSTRACT

The uptake of human papillomavirus (HPV) vaccine remains suboptimal despite being a part of routine vaccination within national immunization program(s). This indicates probable challenges with the implementation of HPV immunization program(s) in various countries. The objective of this systematic literature review (SLR) was to identify implementation strategies for HPV vaccination within national and regional immunization programs worldwide with an aim to provide guidance for countries targeting to increase their HPV vaccine coverage rate (VCR). A comprehensive literature search was conducted across Medline and Embase and included articles published between January 2012 and January 2022. Of the 2,549 articles retrieved, 168 met inclusion criteria and were included in the review. Strategies shown to improve HPV vaccination uptake in the reviewed literature include campaigns to increase community awareness and knowledge of HPV, health care provider trainings, integrating HPV vaccination within school settings, coordinated efforts via multi-sectoral partnerships, and vaccination reminder and recall systems. Findings may help national authorities understand key considerations for HPV vaccination when designing and implementing programs aiming to increase HPV VCR in adolescents.

KEYWORDS:

• Human papillomavirus
• HPV, NIP, HPV vaccine
• HPV strategies
• national immunization program
• regional vaccination program
• vaccine strategies

Introduction

Human papillomavirus (HPV) is highly prevalent globally with 1 in 3 men and 1 in 10 women infected in their lifetime.^1,2 HPV infection can cause anogenital warts, recurrent respiratory papillomatosis, anogenital cancers (cervical, anal, vulvar, vaginal, penile) and head and neck cancers.^2,3 The World Health Organization (WHO) recommends including HPV vaccination within routine vaccination⁴ as part of a coordinated and comprehensive strategy to prevent cancers and other diseases caused by HPV. As of 2022, 117 countries have introduced HPV vaccination into their national immunization program (NIP).⁵

In 2020, the World Health Assembly adopted the global strategy for the elimination of cervical cancer with a strategic target to fully vaccinate 90% of girls by the age of 15 by 2030.⁶ The WHO expanded recommended ages among females and added males within a secondary target group for HPV vaccination.⁷ Despite the strategies in place, implementation of HPV vaccination remains challenged, as evidenced by low HPV vaccine coverage rate (VCR) within the countries that include HPV vaccination in their NIP (21% for girls and 6% for boys in 2022).⁸ Countries seeking to improve HPV program implementation and ultimately vaccine coverage rates may benefit from understanding strategies for HPV vaccination delivery globally.

HPV vaccination strategies refers to operational aspects of incorporating HPV vaccine into a National Immunization Program. Previously published systematic literature reviews (SLRs) provide insights into strategies of HPV vaccination: countries with high VCR tend to utilize school-based vaccination programs,^9–12 systematic vaccination invitations and reminders,^11,12 and dispense the HPV vaccine where they are administered.¹² Countries with low VCRs often vaccinate in public or private health practices and are not using vaccination reminders nor invitations.¹² However, previously published literature is limited by focusing on specific regions, as opposed to taking a global perspective, and focusing on demonstration and pilot studies that have limited generalizability. Additionally, few studies describe the process through which HPV vaccination strategies are implemented, which has been called for in recent literature.¹³

The objective of this SLR is to fill this gap by describing characteristics of HPV vaccination within national and regional immunization programs worldwide. Study findings are intended to help countries understand key considerations for HPV vaccination when designing and implementing programs aiming to increase HPV VCR in adolescents.

Methods

A systematic literature search was conducted to retrieve literature published between January 2012 and January 2022 in the medical bibliographic databases Embase and Medline (via Ovid Platform) using the following keywords: HPV AND (immunization OR vaccination OR NIP OR regional delivery system) AND (delivery location OR parental consent OR community awareness OR human resources OR sustainability OR multisectoral collaboration OR digital information system OR (recall OR reminders) OR equity) AND (vaccination coverage OR vaccine uptake) [Search strategy in Appendices]. The scope of the SLR was determined based on the PICO(+) scheme (Population, Intervention, Comparator, Outcome) framework (Table 1). The search string was informed by results of a preliminary landscape analysis of global vaccine delivery system components within peer-reviewed and gray literature, including the WHO Guide to Introducing HPV Vaccine Into National Immunization Programmes.³

Table 1. PICO(+) framework for scope of systematic literature review.

Category	Details
Population	Countries with NIPs offering HPV vaccine to adolescents
Intervention	HPV vaccination within NIP or other regional programs
Comparator	Not applicable
Outcomes	Primary Outcomes: HPV immunization strategies (information campaigns/community awareness, HPV education, HPV training, systematic vaccination invitations and reminders, HPV VCR monitoring system/digital information system, funding methods) HPV in NIPs or other regional programs HPV delivery system (school-based, community-based, health center-based, in pharmacy, mixed) If and how parental consent is obtained Strategies to increase equity in terms of HPV vaccine access, such as outreach campaigns for underserved population Multisectoral collaboration, such as description of how the ministry of health and ministry of education may collaborate in a school-based program HPV VCR and series completion
Time	January 2012 to January 2022
Study design	Observational studies including: Prospective or retrospective design Registry/database analysis Surveillance Case-control
	Surveys/interviews
	Systematic literature reviews and other reviews
	Programs
	Reports
Language	No restrictions

HPV, human papillomavirus; NIP, National Immunization Program; PICO, Population, Intervention, Comparator, Outcome; VCR, vaccine coverage rates.

Study selection

Each of the records identified during the search was assessed for relevance against predefined eligibility criteria. During an initial screening of titles/abstracts, records clearly not relevant were excluded. Copies of potentially relevant full papers were obtained, and further selection was undertaken based on a full-text review. Double independent record selection was performed during the screening of titles/abstracts as well as full texts. Discrepancies concerning inclusion or exclusion were resolved after discussion between reviewers or through reconciliation by a third reviewer. The selection process was documented at all stages, detailing the reason for exclusion in each case. The selection process was presented in the form of a flow chart based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement (Figure 1). The search strategy, including Medline and Embase summaries are listed in Supplementary Tables A1–A4 [Appendices].

Figure 1. PRISMA flow diagram of the screening and selection process.

*8 records were obtained from gray literature search.

Gray literature

The search in the medical bibliographic databases was supplemented by a search for gray literature related to strategies that address disparities in HPV vaccine access. While the main search included the term “equity,” few publications were identified. Therefore, a gray literature search was conducted to supplement the initial findings. Databases searched are listed in Supplementary Table A4. Keywords used were HPV AND (immunization OR vaccination) AND disparities OR equality.

Data collection

Data from selected papers and gray literature sources were extracted into an Evidence Matrix (Excel spreadsheets) by one investigator. A second reviewer independently reappraised 50% of extracted data. Disagreements were resolved by discussion and consensus finding in which a third reviewer was involved as needed.

Quality assessment

Critical appraisal was carried out using assessment criteria based on the Joanna Briggs Institute (JBI) critical appraisal tools, which assist in assessing the trustworthiness, relevance, and results of published papers. The tool was chosen for its ability to evaluate a variety of study designs. Quality assessment was limited to ~70% of the publications included in SLR and evaluation was based on their study design. The remaining 30% of the publications were not eligible for evaluation because they were abstracts and descriptive reviews.

Results

Of the 168 articles published between 2012 and 2022, ~60% (n = 100) were published within the last 5 y (2018–2022). Articles were predominately focused on North America (n = 78), followed by Europe and Central Asia (n = 31), East Asia & Pacific (n = 15), Africa (n = 8), Latin America & Caribbean (n = 15) and South Asia (n = 2); 29 publications covered data from multiple countries (Supplementary Table A5). Related to income level, most publications (n = 121) focused on high-income countries, followed by lower middle income (n = 8), upper middle income (n = 3), and low income (n = 3); 33 publications covered multiple income levels (Supplementary Table A6).

Characteristics of HPV vaccination strategies

Table 2 lists the HPV vaccination strategies described in the identified articles. In total, 74 articles (65%) described multiple HPV immunization strategies (i.e., a single publication describing delivery location and multi-sectoral collaboration); 40 articles (35%) described a single strategy.

Table 2. Type of strategies in identified papers.

Type of strategy	Number of papers*
The educational strategies	71
Information campaign/Community Awareness	54
HPV training	37
Delivery location	52
Stakeholders’ collaboration	48
Funding	40
HPV VCR monitoring system via information systems	27
Systematic vaccination invitations and reminders	37
Parental consent	17

*There were 74 articles (65%) connected to multiple interventions and 40 articles (35%) to single strategy from research articles.

Educational strategies

A total of 71 publications described the use of educational strategies within HPV vaccine delivery programs across the globe. The literature describes two main strategies – educating the community including parents and children (n = 54) and training of vaccine delivery personnel, such as HCPs and teachers (n = 37).

Community awareness and information strategies: Fifty-four publications specified community awareness and information strategies. The objective of these strategies was to increase awareness about HPV and HPV vaccination, such as the connection between HPV and cancer,¹⁴ benefits of vaccination, effectiveness, safety, and side effects of HPV vaccine^14–17; communicate about new HPV vaccination programs,¹⁷ including catch-up vaccine campaigns¹⁸; and to counter misinformation or vaccine hesitancy crises.^19,20 A variety of channels were described in the publications for increasing awareness and information, including the use of mass media like radio, TV and social media,^{14–17–21–23} distribution of leaflets/brochures,^24–27 public launching ceremonies,^28,29 and government call centers/websites.^30,31 Some publications described hosting community awareness and information sessions within schools, including distributing educational materials to parents and children, hosting informational presentations, and offering the opportunity for adolescents and parents to talk to school nurses or other HCPs about HPV or HPV vaccination.^{16,25,30,32,33} Numerous publications described that the information and awareness campaigns were organized by multi-sectoral groups, including governmental leaders, health authorities, and community and religious leaders.^{25,29,30,34,35} Several publications described community awareness strategies that aimed to decrease disparities. To reach diverse population, including indigenous parents and students, information materials can be written in different languages,³¹ as well as educational sessions hosted held by bilingual people.¹⁵ Also, intersectoral collaboration with participation of civil society and community engagement were key in promoting immunization equity.³⁴ Many studies described that information/awareness strategies led to increased knowledge and support of HPV vaccination programs^36,37 as well as increased vaccine uptake.^{15–17-20–21-31–33-35–37-39–42}

Training of vaccine delivery personnel

The training of vaccine delivery personnel was described in 37 articles. Training strategies were often described in reference to healthcare providers, including physicians and nurses,^{29,43,44,109 110,} school personnel, including teachers and school principals,^{29–30-45–47} and city officials.⁴⁷ The main objective(s) of training(s) included promoting awareness about HPV-related diseases, HPV vaccination effectiveness and safety, support for microplanning of the program’s operation, improve provider skills to deliver effective HPV vaccination recommendations, educate how to effectively remind and recall patients for HPV vaccination.^{18–29–43–48–53} Trainings have been delivered in various formats, including in-person trainings,^44,48,49 online trainings⁴⁹ and, grand rounds lectures.⁴⁴ Numerous publications describe provider trainings to be associated with increased vaccine uptake.^{48–50–52–58}

Delivery location

School-based programs are consistently reported to achieve higher VCR than facility-only-based programs.^{9–15–23–30–59–65} School-based vaccination programs are also associated with reduced socio-economic disparities in HPV vaccine uptake.^60,66 Of note, school-based programs must include strategies for reaching out-of-school-adolescents in order to reduce disparities in vaccine access.¹²

School-based HPV programs are most successful when there is high enrollment and attendance in schools,³⁰ existing vaccination programs within school infrastructure,³⁰ strong collaboration between health and education governmental sectors,⁶⁷ and engagement of school staff, such as principals, teachers, and school nurses.⁶⁸ In particular, school nurses are described as serving a vital role not only in administering the vaccinations^{22–26–68–71} but also educating parents, children, and teachers about HPV and HPV vaccination.¹⁷ The important role of teachers are also commonly described and include assisting with coordinating the immunization sessions and attendance of students,¹⁸ collecting parental consent,⁶⁸ and educating parents and students about HPV and HPV vaccination.^18,38

Health-center-based programs include the delivery of HPV vaccines through public and private clinics, routine care providers (general practitioners, pediatricians, gynecologists, nurses), or via mobile health clinics.^72,73 Health-center-based delivery system was described in 6 articles.^{42–45–60–72–74}

VCR within health-facility-based programs are described in the literature as highly heterogenous.^45,60,72,73 Studies attribute lower VCR within health-center-based programs to challenges in traveling to the health-center within business hours⁴⁵ and having partial reimbursement.^72,74 However, a few articles described situations wherein health-center-based programs achieved higher VCR, and this included full funding and having strong cooperation between education representatives, health service personnel, and municipal authorities from the beginning of the program.⁴⁷ Strategies shown to increase VCR in HCP-based programs include HPV education for parents and adolescents within schools,⁷³ increased availability of HPV-related resources in waiting rooms and exam rooms,⁴² and HCPs providing strong recommendation for HPV vaccination to their patients.⁷³

Eleven articles describe mixed delivery locations^{10–28,29–43–61–75–80} where in the HPV vaccination is offered in more than one location, commonly with schools as the primary vaccination site. Health facilities or special community sites serve as secondary locations for students who missed a dose at school.^28,61,77 A key advantage of mixed delivery locations is that they enable adolescents absent during school vaccination days or who are unavailable in school to be vaccinated in an alternate location.^10,29,77 Mixed-locations are often utilized as a strategy to increase equity by reaching out-of-school girls^28,29,43,75 or other vulnerable populations.²⁹

Stakeholder collaboration

Stakeholders’ collaboration was described in 48 publications. Twelve studies attributed the success of HPV vaccination programs to strong multi-sectoral partnership and coordination.^{12,15,23,24,30,35,45,50,54,56,81,82} Coordinated efforts of health and education authorities, civil societies, and media were identified as factors that could influence vaccination coverage.^{20,23,35,75,83} In contrast, ineffective planning and coordination between stakeholders was described as a factor that could lead to low vaccine coverage.⁶³

There were a variety of key activities organized by multisectoral collaborations, such as the design and execution of HPV awareness and education campaigns and trainings,^{21–22-29–31-42–44-46} and are particularly important for ensuring culturally sensitive and competent messaging.^24,30,84 Of note, 7 articles describe the importance of stakeholder’ collaborations for responding to vaccine hesitancy^16,85 including misinformation,^{20,29,35,36,86} such as by rapidly implementing community re-sensitization plan, which requires constant monitoring and multi-sector collaboration by schools, health workers, and community leaders.²⁹

In particular, collaboration between health and education sectors has been described as integral for school-based HPV vaccination programs.^15,30,81 These collaborations are critical for providing education to parents and children, multi-step coordination, vaccine procurement and distribution, including the planning of vaccine schedules suitable to the school year, and support for teachers and nurses with educational materials.^{15,22,31,34,36,45,47,50,73}

Other critical activities include support with vaccine procurement³⁶; monitoring the adverse events and VCR³⁶; sending reminders and invitations to vaccinations.^28,48,85,87

Funding

Reimbursement of HPV immunization can be grouped as fully funded, partially funded, or not funded by health authorities. An SLR published by Bonanni et al. 2020 reported that HPV VCR tends to be highest when vaccination is fully funded,^88,89 hypothesized to be due to removing barriers to out-of-pocket costs.⁷² Ludwikowska et al.⁷³ and Owsianka et al.⁷⁴ compared funding mechanisms in Poland and reported that HPV vaccination rates were more than 75% with full funding from health authorities, compared to 7.5% with no funding.⁷³ Lefevere et al. reported that in Flanders (Belgium), shift from a strategy consisting of partially funded and non-school-based location to a fully funded and school-based program, not only increased HPV immunization proportions by 0.15 and 0.21 for vaccination initiation and completion, respectively, but also decreased socioeconomic disparity.⁶⁶ However, in countries like Germany and Romania with full reimbursement for HPV vaccination, there still exists low VCR, which may speak to other challenges beyond funding.^76,90

HPV VCR monitoring system via information systems

Twenty-seven papers described HPV VCR monitoring and the information systems in place to facilitate monitoring processes. Vaccine monitoring provides the opportunity to track and respond to trends in vaccine coverage, evaluate the impact of HPV vaccine on HPV-related health outcomes^21,45,50 and identify disparities in vaccine uptake.^28,35,91 HPV VCR monitoring is a routine vaccination tracking process through administrative systems. This monitoring system is crucial for achieving high VCR,²⁴ and incorporates records of individuals already vaccinated and those eligible for vaccination.^{22–24–28–30–35,36-50–74–98} Having a dedicated taskforce comprised of multiple stakeholders to oversee HPV vaccination monitoring has been described as a key component of vaccine monitoring.^{22,24,28,35,44,96}

Various HPV VCR monitoring systems described in the identified articles use registries, District Education Department information or using data of patient population seen for any type of facility visit in the past 2 years.^15,24,53 Immunization rate data can originate from school or clinical registries¹⁵ or dedicated registries for HPV vaccination.⁶⁴ Registries can be either digital, such as state electronic health records,⁵³ state immunization systems,⁵³ schools’ student record database,³³ Ministry of Health (MoH) official recording platform,⁴⁵ or paper-based.¹⁵ Data frequently recorded in HPV vaccine registries include the number and date of HPV vaccine administered, patient age and gender, and any safety reports.^15,45,53 Vaccine monitoring has also been performed in the form of monthly stakeholder meetings⁹⁶ or via The National Immunization Survey – Teen which comprises medical record – verified immunization information including HPV vaccination data.^97,98 Registries have been successfully leveradged for managing follow-up visits for adolescents who were either due or overdue for their HPV vaccine.

Brotherton et al.⁶⁴ highlighted that the majority of countries do not have dedicated registries for tracking HPV VCR, which is a deterrent to accurately measure HPV vaccine eligibility and uptake.^15,64,74 Centralized electronic database are seen as ideal registries^74,99 as it not only enables the recording of doses of vaccine administered but also captures patients’ contact information. This additional information could reduce missed opportunities for vaccination and aid in the communication about follow-up visits required.^63,74,95,100 Additionally, having the ability to disaggregate data at the district-level can be used to monitor socioeconomic inequalities in vaccination coverage.¹⁰¹

Systematic vaccination reminders and recalls

A key strength of having monitoring systems in place is the ability to leverage the information for vaccination reminders and recalls. Vaccination reminders and recalls were described in 37 articles. This strategy can be divided into two segments: parent/adolescent reminders and recall (n = 36) and provider reminders (n = 8). Vaccination reminders and recalls for parents/adolescents are delivered in many formats, including letters or postcards,¹⁰² e-mail,⁴⁸ voicemail,⁴⁷ phone calls,⁴³ Short Message Service (SMS),⁷⁵ or through home visits.⁴³ Content in reminders and recalls have been described as including information that HPV vaccinations were due or late,^43,59,75,109 proposed dates for vaccination,²⁷ location for accessing vaccination,¹⁰² parental consent form,³² vouchers to cover the cost of vaccination,²⁸ contact information,^16,27,28 information on the HPV vaccine,¹⁰² and reminders for subsequent doses.^33,59 Key stakeholders for implementation of reminders and recalls included local governments,^44,50,89 State Medical Officers, healthcare providers and HPV program coordinators,²⁸ and school staff.^24,103 Provider prompts can be in the form of electronic alert systems^25,75,85 or manual checking of vaccination history and sharing information with HCPs through printed notes or daily huddles.^53,75 Reminder and recall strategies are described to positively impact HPV vaccine uptake,^{12,13,19,25,27,41,53,55,57,89,104,105} and in the US both client reminder and recall systems and clinician prompts are recommended by The Advisory Committee on Immunization Practices to improve adolescents’ vaccination rate.¹⁰⁴

Parental consent

The process through which informed consent is obtained is particularly important in non-facility-based settings, like school-based vaccination, where the parents are often not present at time of vaccination.¹⁰ Most publications (n=9) included in this SLR described opt-in parental consent, in which vaccination is rejected by default.^{10,17,24,28,31,43,59,68,91} In addition, two publications compared the success rate with two different forms of delivery of consent forms i.e., opt-in and out-out.^18,106 Consent is often obtained by having adolescents deliver consent forms to parents, obtain signature, and return to students who return the forms to teachers, school nurses, or program staff.^31,68,91 Two articles described consent forms being emailed directly to parents.^28,68

Clave et al. described obtaining opt-in consent from parents to be the biggest barrier to HPV vaccination uptake due to logistical issues such as losing consent papers and low percentage of children returning consent documents.⁹¹ Opt-in consent has also been described as being a barrier within societies where opt-in consent is not the norm, which leads to suspicion and low uptake,^18,106 as occurred in Bhutan.¹⁸ Lengthy consent forms have been associated with decreased vaccination uptake.¹⁰⁶ Strategies to improve the process of obtaining opt-in parental consent include facilitating communication between parents and school nurses to address any questions and concerns,^17,68 bundling consent forms with information about the HPV vaccine,^17,28 simplifying and shortening consent forms,¹⁰⁶ having school staff call parents who refused to provide consent and educate them about HPV vaccination,²⁴ and having reminder systems in place for parents to return consent forms.⁵⁹

Opt-out consent, wherein parental consent for vaccination is accepted by default, was described in 3 articles^29,45,46 and in 2 other articles discussing the positive impact of changing from opt-in to opt-out procedure.^18,106 In a review of HPV consent and social mobilization practices in low- and middle-income countries (LMIC), Kabakama et al.. (2016) reported that opt-in parental consent, though frequently used, resulted in lower reported HPV vaccine coverage than opt-out parental consent.¹⁰⁶ Additionally, when there are challenges with opt-in consent, switching to opt-out consent improves HPV vaccine uptake.^18,106

Furthermore, one article described the possible positive benefits of allowing adolescents to provide consent for HPV vaccination, whereby they described that countries with higher HPV VCR also have laws granting more children their right to autonomy, including allowing children to consent to vaccination.¹⁰⁷

Discussion

This SLR identified 168 articles spanning all geographic regions and income levels that described strategies utilized in HPV immunization programs. As the prevention of cancers caused by HPV is a public health priority, WHO recommends the inclusion of HPV vaccines in NIPs.⁴ Given the challenges of introducing HPV vaccine into NIPs, reviewing real-world data to better understand the components of vaccination programs can help identify various factors and possible solution(s) that may increase the uptake HPV vaccination. Therefore, this SLR identifies and characterizes current practices related to HPV vaccination in national and regional immunization programs. Our findings may help national authorities in understanding key considerations for HPV vaccination programs. There is evidence that the choice of individual components of strategies can influence the success of a program, so it is important to learn from the existing experience. The literature highlights that there is no one-size-fits all approach to HPV vaccine delivery as the success of different strategies vary according to the country-specific context. The ideal delivery strategies for HPV vaccine should be compatible with existing vaccine-delivery infrastructure, affordable and sustainable, and able to achieve highest possible coverage.⁴ Across the literature, an emerging theme was the critical role of schools in increasing access to HPV vaccination. It is widely discussed that school-based vaccination programs have a higher average VCR versus non-school-based programs.^9,79 Our findings also suggest a pivotal role of schools and its staff in other aspects of vaccine delivery beyond administration setting, including HPV education to parents and children,²⁶ collecting parental consent,²⁴ sending vaccine reminder messages, and monitoring vaccination.^24,103 The 2016 WHO Guide to Introducing HPV Vaccine into NIP also states that schools can have an active role in a facility-based delivery strategy. For example, in some countries, schools are notified on a specific day to bring adolescents to the health facility (or nearest scheduled outreach session) for vaccination.⁴ Therefore, countries could consider several ways in which the school and staff would increase access to vaccination in their local context. Additionally, the school staff should be appropriately trained to be involved in planning and implementation of HPV immunization delivery.

The Immunization Agenda 2023 highlights the importance of stakeholder engagement by laying out partnership as one of the four core principles in achieving successful HPV immunization implementation. The agenda calls on immunization stakeholders to align and coordinate activities for improved access to vaccination.¹⁰⁸ The key stakeholders identified in this SLR include partnerships between Ministries of Health and Ministries of Education for school-based delivery, community members such as religious leaders to ensure awareness campaigns are culturally competent, political, media, nonprofit, private organizations and independent individuals (teachers, medical providers).^{21,23,24,29,30,44,54} Saidatul Buang et al. described the success of the Malaysian HPV immunization program by highlighting their multisectoral and characteristics of collaboration among the stakeholders involved.¹⁰⁹ Key stakeholders included academics in universities and institutions, pharmaceutical companies, ministry of health, the public civil society, mass media and politicians, and collaboration was most useful for planning and monitoring program implementation and communication.¹⁰⁹

Findings from the present SLR must be interpreted considering limitations. Most publications included in this SLR focused on high-income countries and North America and Europe, leading to under representation of strategies from LMIC. Results were pooled regardless of geographical location. Therefore, this analysis does not show how strategies are implemented differently depending on a country’s geographic location or income level; this will be explored in future analyses. Despite the limitations, the findings of this SLR makes key contribution to the literature by describing various strategies used in HPV vaccine delivery across all geographic regions and income levels, which can be used by countries seeking to improve their own program implementation.

In summary, this SLR highlights that strategy components that are successful in some countries may not work in others due to differences in society, culture, and politics. For example, opt-in consent works in some settings, but the Bhutanese population’s lack of familiarity with written consent raised suspicions among parents/guardians and threatened to derail the immunization program, leading to a switch to an opt-out approach.¹⁸ Therefore, while the strategies identified in this review are globally recognized, it is imperative for countries to adapt the components of the strategies to their own local context, as suggested by Acampora et al.²⁵ and Crocker-Buque et al.¹⁰⁵ Implementation research is needed to inform the acceptability, adoption, appropriateness, feasibility, fidelity, implementation costs, dissemination, and sustainability of using these different strategies in each setting.

Authors’ contribution

MF, YC, IP, MM, and KN conceptualized the study and designed the study methodology; MM, KN, GS contributed to data collection. MM, KN, and GS led data collection; MAF, YC, MS, CV, IP, MM, KN, GS contributed to data analysis and IP, MM, KN, GS contributed to data validation. MF and IP contributed to study supervision. MF and IP contributed to project administration. All coauthors contributed to manuscript drafting, reviewing it critically for intellectual content, and editing. All authors approved the final version of the report and all authors agree to be accountable for all aspects of the work

Acknowledgments

Editorial support was provided by Preetinder Kaur of Synchrogenix, a Certara Company, under the direction of the authors following Good Publication Practice guidelines (Ann Intern Med 2022;175:1298–1304) and was funded by Merck & Co Inc.

Disclosure statement

Meheret Shumet, Marisa Felsher, Ya-Ting Chen, and Cristinela Velicu reports financial support was provided by Merck & Co Inc. Meheret Shumet reports a relationship with Merck & Co Inc that includes employment. Marisa Felsher, Ya-Ting Chen, and Cristinela Velicu reports a relationship with Merck & Co Inc that includes employment and equity or stocks. Izabela Pieniążek, Magdalena Marzec, Kinga Nowicka, Gabriela Skowronek reports financial support was provided by Arcana Institute, a Certara Company, Cracow office Poland. Izabela Pieniążek, Magdalena Marzec, Gabriela Skowronek reports a relationship with Arcana Institute, a Certara Company, Cracow office Poland that includes employment and equity or stocks. Kinga Nowicka reports a relationship with Arcana Institute, a Certara Company, Cracow office Poland that includes employment.

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website at https://doi.org/10.1080/21645515.2024.2319426.

Additional information

Funding

Employees of Merck Sharp & Dohme, a subsidiary of Merck & Co (Rahway, NJ, USA), the sponsor and funder of the study, were involved in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.