The search identified 1,201 studies after removing duplicates. As a result of the title and abstract screen, 1,045 studies were excluded due to not being an intervention study or not reporting outcomes. The full-text of the remaining 152 articles were reviewed, leading to the exclusion of an additional 72 articles that did not have descriptions of the intervention or outcome data. This resulted in 79 articles included in the review for data extraction (Fig. 1). Table 1 shows the main characteristics of the included studies published between 2015 and 2020.
Study setting and design. Of the 79 intervention articles, 57 (72.2%) were conducted in the U.S. Other studies were conducted in Europe (n = 10, 12.7%), Africa (n = 4, 5.1%), Asia (3, 3.80%), Australia (3, 3.80%), Central/South America (1, 1.27%), and Canada (1, 1.27%). Forty-five studies (57.0%) employed an experimental design, 18 (22.8%) used a quasi-experimental design, and 16 (20.3%) employed a non-experimental design.
Audiences. Intervention settings included clinics (32, 40.5%), schools (26, 32.9%), communities (10, 12.7%), an organization (1, 1.3%), a health insurance system, and online (10, 11.4%). Study samples ranged from 36 to 8,062.
Of the 79 studies, most interventions targeted adolescents only (39 studies, 49%),21–59 of which 15 (38%) included girls only, 17 (44%) included both boys and girls, 3 (8%) included boys only, and 4 (10%) did not report. Other interventions focused on young adults ages 18–34 years (20 studies, 25%),21,22,27,48,50,60−74 parents (27 studies, 34%),22,31,35–37,42,44,52,54–56,59,69,72,75−87 healthcare providers (13 studies, 17%),48,65,79,88−97 or did not report (1 study, 1%).98
Twenty-one interventions included multiple audiences for participants. Common combinations of participants included parents and adolescents (11 studies),31, 35–37,42,44,52, 54–56,59 adolescents and young adults (4 studies),21,27,50,62 clinicians and young adults (1 study),65 parents and young adults (3 studies),22,69,72 parents and clinicians (1 study),79 and clinicians, adolescents, and young adults (1 study).48 Only three studies included only male adolescents or young adult study populations (2 were adolescents only, and the last one was both adolescents and young adults).
Eight of the 79 studies (10.1%) included a large proportion of parents from diverse racial and ethnic identities (defined ≥ 50% other races than White),59,75,77,78,80−83 6 (7.6%) included adolescents from diverse groups,23,30,45,46,51,58 8 (10.1%) included both parents and children from diverse groups,36,37,42,44,52,54,55,64 6 (7.6%) included young adults from diverse groups,28,41,62,67,73, 94 and 1 included both young adults and children from diverse groups (1.3%).27
Socio-ecological Levels. Based on a review of the reported intervention components, the audiences they targeted, and the socio-ecological model, most studies were conducted at the individual level (44, 55.7%), followed by interpersonal level (10, 12.7%), community level (3, 3.8%), and clinic level (4, 5.0%).
Multi-level interventions. Although most interventions were directed at a single level (n = 61, 76.3%), and 23.7% (n = 18) were multi-level. Sixteen (88.9%) combined two levels,23,26,31,40,44,48,50,52,58,59,79,84,90,93,98, 99 and 2 (9.1%) combined three levels (Fig. 2).65,92 Common combinations of the levels included provider and clinical (5 studies),48,50,79,84,93 interpersonal and clinical (4 studies),23,31,90,98 individual and interpersonal (2 studies),26,59 individual and clinical (2 studies),58,99 and individual and community (2 studies).40,52 Meyer et. al aimed to use an electronic point-of-care prompt and 2-hour lecture for providers to increase HPV vaccine uptake in retail clinics (provider and clinical interventions).50 Staras et al. sought to increase HPV vaccine initiation among publicly insured Florida adolescents ages 11–17 using a quasi-experimental factorial design with four study arms: 1) postcard campaign, 2) in-clinic Health Information Technology (HIT) system, 3) postcard campaign and in-clinic HIT system, and 4) usual care (individual and clinical interventions).58 Paskett et al. developed a program focused on HPV vaccine uptake among parents who have adolescent girls ages 9–17 who have not received the HPV vaccine, which would include vaccinations (individual and provider interventions).84 The 3-level combinations included: 1 study with individual, interpersonal, and clinical interventions,92 and 1 study with individual, clinical, and community interventions.65 For example, Malo et al. created a 3-level intervention for parents to analyze which messages were most motivating to persuade them to administer the HPV vaccine to their child, for educating and training physicians, physician assistants, nurse practitioners and nurses who serve at primary clinics specialized in pediatrics or family medicine about the most persuasive messages in speaking to parents about the HPV vaccine for their children (individual, interpersonal, and clinical interventions).92
Intervention Components. The general intervention audiences were parents (12, 15.2%), clinicians (10, 12.7%), adolescents (22, 27.8%), young adults (10, 12.7%), multiple samples (22, 27.8%), and 1 (1.3%) did not report the study sample. The duration of interventions ranged from 10 minutes to 18 months among the studies reporting intervention time frame. Twenty-seven interventions (33.8%) reported the use of theory in intervention development.25, 28–30,34,35,38,39,42,44,49,51,52, 59–61,65,68,70,77,80,81,83,84,86,92,100 Theories or frameworks referenced included the Elaboration Likelihood Model, Culture-centric narrative theory, Health Belief Model, Theory of Reasoned Action/Planned Behavior, Moral Norm and Social Cognitive Theory.
Intervention components varied from education to offering vaccination (vaccine access). The most common intervention components were individual education of parents and/or adolescents (60, 76.0%); use of technology such as websites, PowerPoints, and text messages (21, 26.6%); and provider education (16, 20.3%). Other components included patient reminders (13, 16.5%),23,35,36,43,44,51,54,70,71,74,80,93,98 improving access to the HPV vaccine (6, 7.6%),24,40,45,52,53,71 health systems change (6, 7.6%),31,48,52,58,83,98 incentives (4, 5.1%),33,43,47,56 and community-wide campaigns or outreach (3, 3.8%).26,52,77 Some studies combined two components (29, 36.7%),23–28,30,32,35,40,46,49,53,54,58,61,63,65,70,73,75,77,79,83,86,90,93,95,96 three components (6, 7.6%)36,43,44,48,51,84 or four components (3, 3.8%).52,71,98 Common intervention combinations included education and technology (18 studies, 23%),25,27,28,30,32,36,44,46,49,51,61,63,71,73,75,84,86,96 education and reminders (9 studies, 11%),35,36,43,44,51,54,70,71,98 education and vaccine access (5 studies),24,40,52,53,71 and provider education and technology (4 studies, 5%).48,84,90,95
Community Guide Intervention Categorization.
We report on categorization of the interventions based on the Community Guide’s categorization of health-related evidence-based interventions.11 The most common type of HPV vaccination interventions were informational interventions (25, 31.7%). Of the behavioral interventions, 23 (29.1%)26–30,32−34,36,37,40,42,47,55,56,59,61,62,64,73,81−83 were patient-targeted decision support, 9 (11.4%)35,43,44,51,54,70,71,74,80 were patient-targeted reminders, 12 (15.2%)21,31,48,50,88–93,95,97 were provider-targeted, 8 (10.1%)23,52,53,58,65,79,84,98 were both patient and provider targeted interventions. Only 2 (2.5%)24,45 were related to environmental interventions related to small policies (Fig. 3).
Facilitators and barriers to intervention implementation. Several studies reported facilitators (13 studies, 16.5%)23,24,26,29,30,34,44,46,62,65,77,88,89 and barriers (22 studies, 27.58%)23,29–32,35,42,47,50,51,58,61,62,71,72,74,82,88,89,92,95,98 to intervention implementation. Facilitators included use of patient navigators and user-friendly resources,23,29,62 interactive information sessions,24,88,89 low cost interventions,30,65,88 and quality improvement initiatives.88,89 Barriers to implementation related to cost,23,61,72,74 time constraints related to the given intervention29,31,88,92,95 and integrating the intervention into clinical workflow.50,58,89,95 Other barriers included mobility of parents and technology challenges.
HPV Intervention Outcomes. Forty-two studies (53.2%)21,23,24,26,27,30,32,34–38,40,42–44,47,48,50–55,58,59,61,62,64,65,70,71,73,74,81–84,89,90,93,98 reported on HPV vaccination outcomes, with 38 (48.1%)21,23,24,26,27,30,32,35–38,40,42,43,47,48,50–53,55,58,59,61,62,64,65,70,73,74,81–84,89,90,93,98 reporting HPV vaccine initiation and 26 (32.9%)21,23,24,27,30,34,35,37,40,44,47,51,52,54,55,59,62,64,71,73,74,81,83,89,90,93,98 reporting vaccine series completion. Post-intervention vaccine initiation ranged from 5–99.2%, while series completion ranged from 6.8–93%. For the experimental studies (n = 47), 11 (23.4%) measured vaccine initiation,27,34,36,39,42,53,61,64,70,84, 86 and 3 (6.4%) measured completion.54,71,74 Eleven (23.4%) assessed initiation and completion as outcomes (Table 2).30,32,35,37,38,47,55,59,83,90,93 Of the interventions that only measured vaccine initiation, 3 out of 11 (27%) found a significant increase in vaccine initiation.34,53,84 For the interventions that measured both as an outcome, 3 out of the 11 (27%) found a significant increase in vaccine initiation.35,59,93 Therefore, a total of 6 (12.8%) interventions found significant findings for vaccine initiation.34,35,53,59,84,93 For the interventions that measured both vaccine initiation and completion, 1 (9.1%) found a significant increase for completion only83 and 2 (18.2%) found a significant increase for both vaccine initiation and completion.47,90 Of the interventions with quasi-experimental studies (n = 16), 5 (31.3%) were studies with comparison groups40,43,48,58, 88 and 11 (68.8%) were studies with pre and post intervention data collection (Table 3).21,22,44,50,65,72,73,81,82,91,97 Out of the quasi-experimental interventions with comparison groups (n = 5), 3 (60%) measured vaccine initiation,43,48, 58 and 1 (20%) assessed both initiation and completion.40 Of those, 2 (40%) found a significant increase for vaccine initiation,43,58 0 for completion, and 1 (20%) for both as an outcome.40 Out of the quasi-experimental interventions with pre and post-intervention designs (n = 11), 2 (18.2%) measured initiation,65,82 1 (9.1%) measured completion,44 and 4 (36.4%) assessed both as outcomes.21,50,73,81 One (9.1%) found a significant increase for vaccine initiation65 and 1 (9.1%) for completion;44 and 2 (18.2%) found a significant increase for both.50,81
Table 2
Significant HPV Vaccine Outcomes among Experimental Interventions
Study Design
|
Vaccine Outcomes
|
Significance
|
Multi Component
|
Multi Level
|
Experimental (n = 47)
|
11(23.4%) measured Vaccine Initiation (VI)26,33,35,38,41,52,60,63,69,83,85
|
3 (27.0%) found a significant increase in VI33,52,83
|
|
|
3 (6.4%) measured Vaccine Completion (VC)53,70,73
|
None found a significant increase in VC
|
11 (23.4%) measured Vaccine Initiation and Vaccine Completion (both)29,31,34,36,37,46,54,58,82,89,92
|
3 (27.0%) found significant increase in VI34,58,92
1 (9.1%) found significant increase in VC82
2 (18.2%) found significant increases for both46,89
|
|
Total Significance: 9 total articles had a significant increase in either VI, VC, or both 33,34,46,52,58,82,83,89,92
|
6 (66.7%) were multi component34,52,82,83,89,92
|
4 (44.4%) were multilevel58,83,89,92
|
Table 3
Significant HPV Vaccine Outcomes among Quasi-Experimental Interventions
Study Design
|
Quasi-experimental type
|
Vaccine Outcomes (VI, VC, Both)
|
Significance
|
Multi Component
|
Multi Level
|
Quasi-experimental
(n = 16)
|
Comparison groups39,42,47,57,87
(n = 5; 31.3%)
|
3 (60.0%) measured vaccine initiation (VI)42,47,57
|
2 (40.0%) found a significant increase for VI42,57
|
|
|
None for Vaccine Completion (VC)
|
*NA
|
1 (20.0%) measured Vaccine Initiation and Vaccine Completion (both)39
|
1 (20.0%) found both significantly increased39
|
|
Total Significance: 3 articles had a significant increase in either VI or both39,42,57
|
3 (100%) were multi component studies39,42,57
|
2 (66.7%) were multi-level39,57
|
Pre/Post Test20,21,43,49,64,71,72,80,81,90,96
(n = 11; 68.8%)
|
2 (18.2%) measured Vaccine Initiation (VI)64,81
|
1 (9.1%) found significant increase for VI64
|
|
|
1 (9.1%) measured vaccine completion (VC)43
|
1 (9.1%) found significant increase for VC43
|
4 (36.4%) measured both20,49,72,80
|
2 (18.2%) found a significant increase for both49,80
|
|
Total Significance: 4 total articles had significant increase in either VI, VC, or both43,49,64,80
|
2 (50.0%) studies were multi component43,64
|
3 (75.0%) were multi-level43,49,64
|
Note.. *NA = Not applicable. |
Other common program outcomes included measures of parental knowledge (18, 32.1%), self-efficacy (7, 12.5%), acceptability (7, 12.5%), attitudes and beliefs (6, 10.7%). For adolescents, other outcome measures were knowledge (8, 34.5%), awareness (3, 13.0%), and attitudes and beliefs (3, 13.0%). For young adults, these measures included were knowledge (14, 35.9%), attitudes and beliefs (7, 17.9%), and self-efficacy (4, 10.3%). Out of 79 studies, 15 (19%) measured vaccine intention.
Quality assessment. The study quality (SQ) assessment included 12 items assessed as 0 = no or 1 = yes. The first, SQ1 (the study had a clear objective) was found with the most studies with 79 (98.8%) followed by SQ3 (participants in the study are representative of those who would be eligible) with 68 (85%). Tied in third are SQ2 (eligibility criteria clearly described) and SQ6 (delivered consistently across the study population) with 67 (83.75%) studies. SQ8 (people assessing the outcomes blinded to participants’ exposures /interventions) was found with the least number of articles with a total of 9 (11.25%) studies followed by SQ12 (the study took into account the use of individual-level data to determine effects at the group level) with 15 (18.75%). SQ11 (outcome measured multiple times) with 19 (23.75%) and SQ9 (loss to follow-up after baseline 20% or less) with 30 (37.50%) studies. Generally, most studies were rated as Good (48, 60%), Fair (26, 32.5%) or Poor (6, 0.75%). Supplementary Table 2 presents the quality elements and overall quality scores.