Review team reflexivity

This systematic review engaged a multidisciplinary team of researchers who represented diverse social identities and research experiences pertinent to the topic. Academic disciplines represented include health promotion sciences, epidemiology, and medical anthropology. Full details of the review team are documented in the protocol paper for this manuscript [26].

Study eligibility criteria

This review evaluated primary studies that reported on the perspectives, factors and/or decision-making processes of young adults aged 18–26 years. The inclusion and exclusion criteria for this review as aligned with the protocol follow below.

Information sources and search strategy

We searched the following seven (7) electronic databases to identify studies for inclusion: PubMed, SCOPUS (Elsevier), Embase (Elsevier), the Cochrane Library (Wiley), PsycINFO (EBSCOhost), CINAHL (EBSCOhost) and CABI Global Health (EBSCOhost). No search restrictions were posed on geographic region/country where studies were conducted, nor on language of the manuscript. A comprehensive search strategy was developed and adapted for each database. Key words and Medical Subject Headings (MeSH) terms were combined related to “HPV”, “vaccination”, “young adults” and qualitative methodological filters (e.g., “focus group”, “interview”). Full details of the search terms for each database are details in S1 Appendix.

All databases were searched by NMM with support from DJM beginning in 2006 (the year HPV vaccines were publicly available) up to the date of the search. The initial search was conducted on May 11, 2023. Updates were made to the search terms following peer review feedback on the protocol manuscript and the search was rerun on October 12, 2023. As screening procedures had commenced following the initial search, we followed the procedures outlined by Bramer & Bain [27] to identify the new records retrieved from the updated search (S2 Appendix). Lastly, the reference lists of all eligible studies were also manually searched to identify additional studies for inclusion.

Selection of studies

The citation manager software EndNote (Clarivate, London, UK) was used to manage and deduplicate all the studies identified through the electronic database search. The deduplicated citation file was then imported into the literature review software DistillerSR (Evidence Partners, Ontario, Canada) for screening in accordance with the review protocol. DistillerSR further identified additional duplicate records which were removed using the software’s functionality.

Studies were screened through a title/abstract review stage and a full text review stage to ascertain inclusion as guided by the eligibility criteria. Each study was independently assessed by two review authors at each screening stage. Any disagreements in evaluation were resolved by discussion and consensus between reviewers. While there were no language restrictions implemented during the database search, there were two non-English full text articles obtained (one Korean and one Spanish). To facilitate the review for inclusion, Google Translate was initially used to aid with reviewing the methods section of the articles. It was determined that both articles did not meet inclusion criteria at full text and were subsequently excluded. After the two stages of screening, 71 articles met the review eligibility criteria for consideration to be included in the review.

Sampling of studies

In QES, managing the volume of data examined is crucial to uphold analysis quality [28]. Maximizing the heterogeneity of identified themes and concepts to foster a more profound understanding of the research subject is prioritized over exhaustively assessing every study [29]. Consequently, purposively sampling methods were used to aid the management and analysis of the qualitative data to be extracted. In alignment with the approaches taken by other qualitative review authors [30], we purposively sampled a subset of the studies for analysis, using an approach called criterion sampling [31,32], in which studies are sampled based on meeting predetermined criteria. Given the aim of the review was to understand HPV catchup vaccination in individuals aged 18–26, the age criterion employed for sampling inclusion was that studies exclusively recruited participants 18–26 years old. We believed that this sampling criterion would best facilitate obtaining focused and rich information essential to the research question. Forty-five (45) articles were included in the review following purposive sampling.

Data Extraction

The data extraction process was performed in 2 steps, an adjustment from the original protocol. Step 1 was the extraction of the study characteristics, and step 2 was the extraction of qualitative data. Aligned with the protocol, step 1 of data extraction was performed in DistillerSR, using a data extraction form specifically created for this review. Two reviewers independently extracted data from each study and discrepancies were resolved by a third reviewer. The study characteristics data extracted from eligible studies at step 1 were:

• publication year
• data collection year
• context (study country; rural vs urban)
• participants (number of participants; demographic characteristics, e.g., age, gender, race/ethnicity, sexual orientation)
• study design (objective/research question, sample recruitment, data collection methods, theory frameworks or conceptual models used, analysis methods, funding)

All articles that met review eligibility (n=71) had their data extracted at step 1. This was done to be transparent about the existing literature that was applicable to research question, even though we may not report on all of it for this review.

Step 2 of the data extraction process was conducted in REDCap (Research Electronic Data Capture) [33] as the review team found it was better suited to handle qualitative data. This step was performed only on the included articles that met the criterion sampling (n=45). The information extracted in step 2 were 1) the themes or constructs developed by the primary study authors, including any contextual explanation for how the themes/concepts were defined by the primary authors; and 2) verbatim participant quotes provided. For consistency in how the qualitative data were extracted across all the articles, step 2 data extraction was performed by one review author (NMM).

Assessment of the methodological limitations of included studies

The methodological limitations of each included study was independently assessed by two review authors using the Critical Appraisal Skills Programme (CASP) quality assessment tool for qualitative studies [34]. An adapted version of the tool was used as guided by other reviews [28,35,36] and was piloted on a subset of studies to assess feasibility and integrity of the assessment. Disagreements were resolved by a third review author.

Data synthesis

We used Braun and Clark’s methodological process of thematic analysis to analyze and synthesize the qualitative data [37]. Data was analyzed using qualitative analysis software Dedoose version 9.2.005. The following stages of thematic analysis were undertaken:

• Familiarization: Three review authors (NMM, JS, FNM) reviewed all the extracted data. Notes were taken on the impression of the data.
• Generating initial codes: The aforementioned review authors initially coded data from three different studies that had the largest amount of data extracted, to inductively identify and generate initial codes; codes were also formed from the notes taken during the familiarization stage. After this initial coding, the review authors met to discuss the codes identified, consolidate any duplicate codes, and finalize the codebook. Another round of coding was performed on three additional studies to verify the codebook; no new codes emerged. Each study was then independently coded by two review authors. During the coding process, authors were able to take additional notes in Dedoose pertaining to trends and observations they noticed as they coded. After coding, the two review authors assigned to each study met to discuss any discrepancies in coding and decide the finalized version of the coded data.
• Generating, reviewing, and finalizing themes: Once all the data were coded, review author NMM generated the initial themes and subthemes from the codes, and any notes take from the coding process. The initial themes generated formed the basis of the review findings which were subsequently reviewed and revised by the other authors involved in the coding process (JS, FNM).

Assessment of confidence in synthesized findings

As recommended by the Cochrane handbook on QES, we used the GRADE- CERQual (Grading of Recommendations Assessment, Development and Evaluation - Confidence in the Evidence from Reviews of Qualitative research) [38] to evaluate the confidence in synthesized findings. The CERQual confidence assessment is based on the following four key components:

• Methodological limitations of included studies: the extent to which there were concerns about the design or conduct of the primary studies that contributed evidence to an individual review finding [39].
• Coherence of the review finding: an assessment of how clear and cogent (i.e., well-supported or compelling) the fit was between the data from the primary studies and a review finding that synthesized those data [40]
• Adequacy of the data contributing to a review finding: an overall determination of the degree of richness and quantity of data supporting a review finding [41].
• Relevance of the included studies to the review question: the extent to which the body of evidence from the primary studies supporting a review finding was applicable to the context (perspective or population, phenomenon of interest, setting) specified in the review question [42].

To facilitate this process, we used the GRADE-CERQual Interactive Summary of Qualitative Findings [43]. It is noteworthy that the evaluation of methodological limitations of the included studies was not used to exclude studies from the review, but we did consider them in the assessment of confidence for the review findings. After evaluating each of the four components, we made a judgement on the overall confidence in each review finding; all findings started at ‘high confidence’ and then were graded down to ‘medium,’, ‘low’ or ‘very low’ confidence based on any concerns arising from the CERQual components [44].

Results of the search and screening

We identified 1163 titles from the search of seven databases and considered 208 articles for full text review. We identified 71 articles representing 68 studies that met the review eligibility criteria. After applying purposive sampling, 45 articles representing 42 studies were included and synthesized in the review. There were 3 pairs of eligible articles that reported results from the same primary study; all three pairs were purposively sampled. The results of the search, screening, and sampling process are detailed in the PRISMA flow diagram (Fig 1).

Description of eligible studies

This section details the study characteristics for all 68 eligible studies that met review eligibility criteria to help characterize the state of the existing qualitative literature related to HPV vaccination among young adults. Table 1 details the study characteristics of each eligible study.

Methodological quality of included studies

Across the 42 studies that were purposively sampled and included in the review, the majority (35 studies represented by 37 articles) had an overall assessment of minor to moderate quality (Table 3) The most common issue across the studies was poor or no reporting of researcher reflexivity (36 studies). It is worth noting that the requirement for reflexivity in reporting guidelines for qualitive research may have been implemented after some of the studies were published. Additionally, three studies did not provide details on data analysis procedures and failed to take ethical issues into consideration (no mention of informed consent or IRB approval) [46,55,76]. Of the 42 included studies, only two studies had severe concerns on methodological quality [46,55].

Confidence in review findings

Our QES yielded 29 review findings. We graded 11 findings as high confidence, 17 findings as moderate confidence and 1 finding as low confidence (Table 4). The GRADE CERQual evidence profile detailing our evaluation of each component for each finding and associated explanations are in S3 Appendix.

Synthesis of findings

This section details the review findings from the QES. The review findings are categorized into 10 thematic categories that emerged from the thematic data analysis process to reflect the barriers and facilitators to HPV vaccine uptake and decision-making processes among young adults. While the individual findings are presented as distinct elements with a specific theme, we acknowledge that findings may also fit or overlap with other thematic categories. The thematic categories include:

• Individual factors: influence of personal attitudes or beliefs on decision-making
• Alternatives to vaccination: behaviors/practices believed to be alternatives to the HPV vaccine
• Knowledge and information: knowledge and information about HPV/HPV vaccine
• Sex and romantic relationships: influence of sexual status and relations on decision-making
• Parents and peers: role of parents/peers in decision-making
• Physicians: role of physicians in decision-making
• Logistics: factors associated with the process of getting vaccinated
• The vaccine: components about the HPV vaccine influential in decision-making
• Gendered perceptions and bias: influence of gendered views on promotion and uptake
• Government and policy: role of government in decision-making

Theme 1: Individual factors

Finding 1. Missed opportunity: Some young adults believed they missed the window for vaccination because they were too old to benefit from it. Studies reported that some young adults believed they were too old to receive the HPV vaccine. This was due to lack of clarity about the vaccine’s efficacy past certain ages [65,72,108,110]: “I heard that the HPV vaccination works on girls prior to age 15. It is too late for me to benefit from the vaccination because I am too old and have been sexually active” [108]. Some participants also believed the vaccine could cause adverse reactions when administered after certain ages [69] or associated the vaccine as one typically administered in childhood and subsequently no longer applicable when older:

“When I came to college, people were saying, “Oh, I got the HPV vaccine recently,” or whatever. I, like, “You’re 20-something years old. What do you mean you just got it?” I just thought it was one of those things that you just get when you’re young, like measles and like smallpox and all those vaccines.” [72]

Finding 2. Low risk perception: Some young adults believed they were not at risk for HPV-related illnesses or that they still had time to decide on vaccination. Personal risk perception played an influential role in vaccine decision-making, with some participants feeling they were low risk for HPV-related diseases to justify vaccination [45,66,75,81,110]: “I think more the reason I just didn’t get [vaccinated] was just because - yeah, I guess you’re kind of right, since I was thinking, oh, it’s not that big of a deal for me. Maybe this isn’t a vaccine I 100 percent need to get right now” [81]. Some young adults did not perceive the urgency to need to get vaccinated or believed it would never be too late for them to get vaccinated[67,101]: “Since you can get vaccinated up to age 26, I have 5 more years to think about it” [67].

Finding 3. Proactive measure: Many young adults viewed vaccination as a proactive measure to safeguard their health in the present and prevent future regret if they didn’t get vaccinated. Many young adults expressed a desire to protect themselves from cervical cancer [64,67,71,89,100,103] other diseases associated with HPV [52,71,89,106,110]: “When I heard what the shot can help prevent- cervical cancer - I wanted to get it” [67]. Some individuals recalled learning about HPV and the vaccine during specific life events, such as pregnancy/health diagnoses which served as the cue to action to get vaccinated [47,113]: “I kind of panicked a little bit when I was diagnosed with HIV, but then I’m like, OK, I’m getting everything. So it’s like -- I got it [HPV vaccine]” [47]. Participants who had experienced HPV-related symptoms expressed an increased interest in vaccination [60,78]: “I started developing symptoms (warts), I kind of had a suspicion that’s what it was. I thought I wouldn’t be really suited for the vaccine, but then my doctor said that it might actually help” [60].

Concerns about long-term health and future relationships drove some individuals to prioritize HPV prevention and avoid future regret [64,106]:

“…I didn’t want to eventually be married and have that, you know, worry in my mind about HPV.” [106]

‘‘I think it would be a good thing to do. Instead of sitting there and be like ‘‘ok, I’m not gonna do it, then then all of a sudden you go to the doctor and they say you have cancer, you gonna think back like, ‘‘Oh I should’ve continued the shots instead of doing all that.“ [64]

Finding 4. Low-stakes preventive measure: Several individuals mention the simplicity of the decision to get vaccinated, seeing it as a low-risk preventive measure with potentially significant benefits [54,64,72,75,78,89]

“Well, it doesn’t take much to vaccinate people, so I guess it is helpful. Just go and get a shot and you are all set.” [89]

“There is no harm in getting the vaccine. It’s a preventive measure. It’s like one of those there’s nothing to lose type of thing.” [72]

Theme 2: Alternatives to vaccination

Finding 5. Reliance on pap smears: Young adult women believed that regular Pap testing negated the need for HPV vaccination. Some young adult women believe regular cervical cancer screenings were sufficient to monitor their sexual health, with many questioning the necessity for vaccination if they still had to continue getting screened [65,76,88,108]: “Cervical cancer is treat-able if caught early, so there would be no need to get a vaccine if you are doing an annual Pap smear” (US) [65]. In one study of participants from multiple countries, female participants also express costed savings from not getting vaccinated and just getting screened:

“Screening is something that might be...even more effective, then if you keep track you’re going to avoid it and all that. Had I known it earlier, we would have saved a lot of money from vaccines [laughter]. If I’m going to have my check, what’s the use of it?” [88]

Finding 6. Condom use and other precautions: Young adults expressed precautions such as condom use, abstinence, and decisions on sexual partners were sufficient to protect against HPV, rendering the vaccine unnecessary. Some participants believed that making selective decisions about who to have sexual relations with and using barrier methods are effective in preventing HPV infection, leading to a perception that vaccination is unnecessary [67,108]:

“My mother said to just not be stupid about sex … I’m not an idiot about who I sleep with. I really feel like HPV only affects people who don’t make smart decisions. If there are condoms out there today, use a condom. … I feel like there are other ways to prevent HPV… less serious ways than getting the vaccine.” [67]

Condom use was highlighted as a primary method of protection against HPV [67,81,89,108] as exemplified by statements such as “I feel like condoms will protect me” [67] and “I typically wear condoms so I’m not particularly worried about it” [89]. Some individuals also expressed confidence in abstinence as a means of HPV prevention, questioning the need for vaccination [80,106]: “I am abstinent, why should I get it?” [80]

Theme 3: Knowledge and Information

Finding 7. Many young adults expressed having insufficient information on HPV or the vaccine before deciding to get vaccinated. There was an expressed desire more information about HPV and the HPV vaccine. Young adults expressed concerns about not knowing enough about HPV or the vaccine [58,59,65,71,72,81,96]. Some participants demonstrated a lack of information on HPV transmission [54,62,63], how the vaccine works [54,60,78], and the association between HPV and cervical cancer [64].

If I have more information about the vaccine...I would probably get it …. As the old adage says, it is better to look before you leap. If I have more information about the vaccine, I’m willing to get it, but I don’t know what it is very well.” [72]

Some young adults admitted that they had never heard of HPV before vaccination or receiving the HPV vaccine without understanding what HPV is or how it is transmitted and others [54,58]: “I have no idea what it is honestly, I got the Gardasil shot...... my mom wanted me to... but I don’t know anything about it” [54].

Participants expressed a desire for more information and awareness of HPV and the vaccine [65,72], which ranged from general knowledge about the benefits of the vaccine [58,59] to more scientific/research- related information on the vaccine [66,89]: “It’d be very unlikely (to accept the vaccine) because I’d have to-like I said earlier-I’d have to go on the Internet and just see what has other researchers come up with and other studies and other experiments on it-what would all that calculate to” [89].

Theme 4: Sex and romantic relationships

Finding 8. Sexual activity and behavior: Some individuals believe that vaccination against HPV is only necessary if one plans to engage in sexual activity or has many sexual partners. Some young adults expressed a lack of perceived need for vaccination because they were not currently sexually active and therefore did not need the vaccine [54,59,63,64,71,75,101,103,106]: “I have no sexual experience, so I do not think I am at risk of getting cervical cancer. Cervical cancer is caused by sexual intercourse. I think those who plan to have sex may find the vaccine more useful. There is no need for me to get vaccinated if I do not have sex or get married in the near future.” [101]

Additionally, young adults also believed that people who had a lot of sex partners should get vaccinated [67,81,88,106,110]: “So, it will make sense to do it if you are going to be out here just engaging in a lot of sex with a lot of people, it makes sense to protect your-self” [81].

Finding 9. Relationship status influenced risk perception and subsequent vaccination behavior among young adults. Many young adults in committed or monogamous relationships often perceived themselves to be safer and perceived being at lower risk for HPV infection, thereby negating the need for HPV vaccination[67,78,80,81,89,106]: “I feel like if I were in - I don’t know like single or perhaps in like a non-exclusive relationship, it’s something that I would think about a little bit more. But as - yeah, I’m just like - it - it hasn’t really felt as relevant for me, but I definitely think that there’s like a lot of benefits to it” [106]. Conversely, a few young adults expressed interest in vaccination or that they did get vaccinated because of the additional safety and protection it offered even if they were in a relationship [106,107]: “Yes, only because like we were sexually active, and I was like any kind of like extra protection I was game for. He -he had been with other people before, and I’m like you can’t really tell when somebody has HPV; he might not even know” (P19, single and dating, vaccinated) [106]. Changes in relationship status also appeared influential. Some participants indicated they would consider getting vaccinated if they became single [81] while others expressed that they got vaccinated after their relationship status changed: “I wasn’t going to get it, but I broke up with my boyfriend. That’s when I had my first shot” [67].

Finding 10. Parental beliefs about sex and the HPV vaccine influenced young adults’ vaccine attitudes and decisions. Participants reported feeling influenced by their parents’ beliefs regarding vaccination and sexual behavior. Parental beliefs included perceptions that getting the HPV vaccine advocates having sex [58,65,67,79,100,101]; monogamous relationships negate the need for vaccination [67]; or attitudes about morality and protecting one’s virginity till marriage [101]. In these cases, young adults were deterred from getting seeking vaccination.

“My mother was very anxious after learning that I wanted to have the cervical cancer vaccine. She said only girls who want to do something bad [have sex] want to have such vaccination, and there is no need for me to do so. My mother said it is important for good girls to protect their virginity until they get married. The reaction of my mother was so strong that it made me dare not mention it again.” [101]

Theme 5: Parents and peers

Finding 11. Mothers more than fathers played an active role in HPV vaccination process among young adults. Many participants cited their mothers as significant sources of influence in getting the vaccine, through providing information and advice, conducting research before vaccination, and advocating for their children to receive it [48,54,59,60,64,67,72,75,102]. Mothers also facilitated important cues to action such as scheduling vaccination appointments, demonstrating their active involvement in the vaccination process [67,81,96]: “Just every time I go in for a vaccine, my mom set the appointments. I just go and get the shot; get a nice little bandage and leave” [81]. Some participants expressed that their mothers played a crucial role in advocating for HPV vaccination in situations where other family members such as fathers were more reluctant and hesitant about the necessity of vaccination for their child [54,78]: “And my dad was just kind of furious [about the cost and need if she wasn’t sexually active] and then... My mom was like, yeah... we need to get these and it was all okay” [54].

Finding 12. Decision-making power: There was a mix of deferred or shared the decision to get vaccinated between young adults and parents. Some participants deferred vaccination decisions to their parents, particularly their mothers, trusting their understanding of healthcare information and recommendations [54,64,81]: “Anything else again any new vaccines or any diseases going around I actually leave that with my mom. Cause she will better understand what people are saying than what I would.“ (Male 18, non-initiator) [64]. In other instances, some young adults engaged in discussion and shared decision-making with their parents when considering vaccination [82,103]: “I’ve discussed it with my parents but we all agreed we wanted to wait a couple more years to see what the side effects were” [103].

Finding 13. Peer influence: Friends and acquaintances played a significant role in shaping vaccination decisions. Young adults who believed their peers were vaccinated or had friend groups of people who were vaccinated expressed favorable vaccine attitudes and willingness to get vaccinated [54,63,67,96,107]: “My mom didn’t want me to get it done but I thought everyone else is getting it done so I might as well” [96]. Friends were also seen as a trust source of vaccine information which influenced uptake, and, in some instances, friends would decide to get vaccinated together [48,54]: “One day I was just talking in the group chat, and I [asked] my friend “Oh, who hasn’t gotten cervical cancer jab? I’m thinking of getting it.” One of my friends said that she hasn’t gotten the jab as well, and then she also expressed her interest of getting it. So I said, “Why not we just go together?” She did all the research about the vaccine and then I just followed along” [48].

Conversely, some young adults described instances where negative reactions or perceived negative perceptions from their friends deterred them from getting vaccinated [101,110]: “Some of the friends that I do have in particular would probably think that I’m just being extremely promiscuous sleeping around with guys like every night.” [110]

Finding 14. Health history of family and friends was a motivating factor in the decision to get vaccinated. Concerns about cancer given family history or observing others battled HPV-related illnesses emerged as a motivator for vaccination among some participants [52,63,89,103,113]:

“Having seen my friend going through having HPV I think it’s a pretty terrible thing to go through and it affects who she chooses as a future partner, she’s a single woman, right. So it’s going to affect how her relationships end up unravelling and that sort of thing and whom she meets. I mean a world without HPV would be nice. But I guess my own concern about my sexual health outweighed any of the potential problems that might come with it.” [113]

Theme 6: Physicians

Finding 15. Doctor recommendation: Physician recommendations (positive or negative) were influential in vaccination uptake. Many young adults cited their doctor’s positive recommendation as a significant factor in their decision to get vaccinated, viewing it as essential for their health and trusting their expertise [47,51,54,60,64,67,69,71,81,89,96,106,113]: “It was the doctor’s recommendation. I honestly wouldn’t have thought about it had he not recommended it” [60]. Participants expressed trust and confidence in their doctors’ recommendations, seeing them as experts whose advice should be followed for health-related matters [48,71,89,102,107,110].

Conversely, some individuals reported their doctor either advising against vaccination [53,54,69], or never mentioned or offered the vaccine [67,69,71,79]:

“I didn’t get it [the HPV vaccine]... because my doctor told me it wasn’t necessary if I wasn’t sexually active or anything.” [54]

“I talked to my doctor, and he honestly told me it was basically that...if people have not been getting the shots and not been getting cancer for a long time and it doesn’t run in my family, I don’t have a high probability of having it.” [53]

Finding 16. Communication gap with doctors: Young adults desired better communication and more informed conversations with their doctors. Some participants felt that doctors were reluctant to provide detailed information unless prompted, leading to uncertainty and frustration about where to find trustworthy information [69,82,88,101]:

I : So when you did bring [HPV] up to your doctor, did she talk to you at all about the virus?

P: No, not at all...She was like “I guess you’re sexually active, like you can get it if you want it.”...I think this was before I was sexually active, because this was like my annual physical freshman year of college, and I brought it up and I’m like “This is something I read I needed,” and she didn’t talk about side effects, she didn’t talk about what can come with it, it was like me advocating for myself and she was like “You can get it if you want but like you’re gonna have to pay out of pocket.” [69]

Participants expressed a need for open, non-judgmental communication with healthcare providers, where they could ask questions, receive thorough explanations and comprehensive information about the vaccine, be treated respectfully and not feel rushed [47,58,59,89]:

“The first time I was offered the HPV vaccine, I just said no, because I didn’t understand what the doctor said. Some of the terms I didn’t understand, and she just spoke brief about it. I was shy at the time, too shy to ask any questions. I saw her [provider] in a hurry, and I was like, “Oh yeah, I understand,” but in reality, I didn’t. I just said that because she seemed in a hurry.” [59]

Participants also stressed the importance of providers creating a safe and non-judgmental environment particularly given stigma and discomfort around discussing sexual health [58,89]: “There is still some taboo feeling with discussing sex with anybody so I think it’s really important that the doctor listen and be understanding of any responses that the patient might give.” [89]. This was particularly important for LGBTQ+ participants who highlighted the importance of LGBTQ+ Inclusive healthcare and preferences of receiving care from LGBTQ+ friendly healthcare providers [47,110]: “A gay provider would be more into or up-to-date with newer things that are coming out. Especially like with the threats that are more for the gay lifestyle. Because I really don’t think that my health provider would know about HPV” [110].

Theme 7: Logistics

Finding 17. Appointments: Scheduling and appointment challenges impacted young adults’ ability to get vaccinated. Participants described difficulties in completing the vaccine series due to busy schedules and other responsibilities which made it a challenge finding time to go get vaccinated [47,63,64,69,82,102,103,105]. Young adults expressed interest in combining HPV vaccination with other medical visits such as annual physicals to streamline the process and make it more convenient [58,69,89,105]: “It would be hard for me to schedule an appointment to complete the HPV vaccine series. It would be easy to get the HPV vaccine if offered during my clinic visits” [105]. For some participants, HPV vaccination was simply not a priority to make an effort for [69,103]: “I never got around to it and to be honest I don’t think it’s a big deal to change my schedule for’‘ [103].

Finding 18. Multiple shots: Some young adults found the process of going back multiple times for the three doses burdensome, leading to forgetfulness or avoidance. Challenges with appointments were compounded by the need for multiple visits to complete the HPV vaccine series which young adults found inconvenient [47 67,69,75,81,105]:

‘‘It’s so troublesome…it’s not like maybe 3 times a week you can get it over and done with. It’s over more than a year, it’s really long…” [75]

“I would have gotten it… it’s just that getting three shots across nine months is a hassle, and I’ve been moving around a lot in the last couple of years” [67]

Some participants were unclear about the number of doses required for the HPV vaccine and what to do if they missed doses, leading to missed opportunities for completion [63,96]: “didn’t even know there were three shots involved with it until I came in” [63].

Finding 19. Accessibility: Transportation and access challenges hindered HPV vaccination uptake. Participants cited lack of transportation or long distances as barriers to HPV vaccination [55,64,65,67,82]. Alternative locations such as pharmacies, emergency rooms or vaccine drives in atypical settings were also discussed as preferred venues to receive the HPV vaccine and increase accessibility to get vaccinated [64,82,96,110]. For some participants on college campuses, research authors noted there seemed to be an unawareness of the vaccine availability at the local campus clinic [64,75].

Finding 20. Reminders: Reminders were cited as helpful in ensuring adherence to the vaccination schedule. Whether from providers or parents, or personal calendar systems to track information, young adults relied on reminders to aid them remember appointments and get vaccinated [47,64,96]. Several individuals mention that their mothers were responsible for scheduling their vaccine appointments, indicating a dependency on family members for healthcare management [67,81,96]: “It was up to my mom to book the appointment -again” [96].

Finding 21. Mandates: Young adults had mixed views on mandates for HPV vaccination. Some participants opposed mandates for HPV vaccination [71,92]. Other participants expressed compliance with mandates as part of requirements for school enrollment [64,81,100], support of public safety efforts [89], or trust in the government making vaccination compulsory [75].

Theme 8: The vaccine

Finding 22. Vaccine cost: Young adults expressed concerns about paying for the HPV vaccine, citing high out-of-pocket costs and need for government subsidies. Participants expressed difficulties in paying the cost for the vaccine series and subsequently opting out of vaccination [51,52,62,64,67,75,81,96,101,105,108]. Young adults also highlighted the impact of insurance coverage on their ability to afford the vaccine and decision to get vaccinated [53,63,65,89,108,110].

“”The vaccine is too expensive. It costs almost my whole monthly wages from my part-time job. If I really have the need, I would not mind spending my wages on the vaccination. However, I am still unmarried so I do not think I have the need at this moment. Spending such a large amount of money on a vaccine that is not useful for me at this moment is not worthwhile.” [101]

I would have received the HPV vaccination if my health insurance covered it at that time or if the government paid for the HPV vaccination.” [108]

Parental willingness or refusal to pay was also influential in the decision to get vaccinated [54,67,75,100,101]:

“My mother said there is no use for me to get vaccinated except if I want to do something inappropriate [having sex]. As my mother discourages me to get vaccinated, I will not have it because she will not pay for it or sponsor me. I just have one part-time job but the wages are insufficient to pay for the vaccination.” [101]

Don’t know [how much I would be willing to pay for the vaccine]. Depends on how much parents will be willing to spend!” [100]

Young adults called for governments to subsidize the cost of the vaccine, suggesting it would encourage more people to get vaccinated [51,52,75,96]: “The main concern is the price. If the government provides more subsidies to make the vaccine cheaper, maybe (reducing) several hundred or hundred and something, it may make people more willing to be vaccinated” [51].

Finding 23. Side effects: Young adults expressed concerned about the side effects of the HPV vaccine. Across many studies, participants expressed worries about potential side effects of vaccines. Participants were concerned about not knowing the long-term effects of the vaccine or how the vaccine will affect them [51,59,65,76]. Young adults were also concerned about the (unknown) ingredients of the vaccine and not wanting them in their body [59,64,71,72]. Concerns about the vaccines side effects were also fueled by the negative stories and experiences others had of getting vaccinated [54,65,69,88,101,103].

“I trust my body. To be honest, I don’t feel comfortable having it [HPV vaccine] in my body. I feel like I don’t need it. I’m not even active [sexually] like that. I don’t want to put something in my body if I don’t know how it’s going to affect me. I’d rather not risk it. I’m actually kind of scared to even do it” [59]

“Only one or two friends of mine have had the cervical cancer vaccine; they commented the shot was particularly more painful than other vaccines. Also, one of my friends suffered from fever, dizziness, extreme tiredness and a rash for some days just after the first dose, and she dared not continue the remaining course, so I do not think about receiving the vaccine at this moment.” [101]

Finding 24. Understanding of vaccine effectiveness: Young adults questioned the effectiveness of the HPV vaccine given the limited strains it covers and lack of 100% protection. Doubts about the effectiveness of vaccines were expressed particularly given the vaccine does not guaranteeing 100% protection [62,76,106,110,115]: “Um, of course, now it’s [risk for HPV] definitely much, much lower. There’s still a risk because the vaccine doesn’t work 100 percent,” [106]. In one study where participants had also received cytology testing, individuals with abnormal cytology results who also received the vaccine expressed frustration with the vaccine: “The vaccine was a waste of time. I would say it’s pointless and it’s not doing what it’s supposed to” [115].

Some young adults also questioned the usefulness of vaccines if they were already sexually active or have had multiple partners, which they felt potentially negated the vaccine’s effectiveness [76,88,115]: “Well, we are already sexually active, and you are supposed to get the vaccine before you become active, because then it is most....I forgot the word... most effective. Actually, at this point, you can’t be sure about the effectiveness of the vaccine” [88].

Additionally, the knowledge that the HPV vaccine only protects against specific strains of HPV led some young adults to believe this undermined the effectiveness of the vaccine[54,65,96]:

‘‘You’ve got to take into consideration that vaccination is only preventative for certain kinds of HPV.’‘ [65]

“... because like what’s going on with swine flu right now and how they will vaccine like one part of the disease... but then there’ll be another outbreak of a different [type] so I kind of think about that with the HPV; like what if they vaccinate me and I still get cervical cancer, like a different type of cervical cancer so that why I’m leery…” [54]

Finding 25. Development of the vaccine: Concerns were raised about the vaccine’s novelty, hastened development, and lack of long-term studies. Some participants believed the vaccine development was rushed [54,88,113] and many others cited the absence of long-term studies on the vaccine’s effects, and subsequent wariness about being early adopters or “guinea pigs” for the vaccine [54,62,64,67,115]. Young adults also expressed concerns about the vaccine’s safety and efficacy, emphasizing the need for longer investigation to determine potential side effects and effectiveness [51,66,67,75,88,108,113].

“against it because it just wasn’t very tested; it seemed to me like they approved it before they even were finished testing it in everybody and I thought that was really jumping the gun and not very safe […] the regular vaccines like that you get through public school and... ones that have been around for a long time, I’m not that worried about. But since this is so new... that makes me kind of nervous.” [54]

“... I know that this vaccine has not been introduced for long, only around 10 years. Therefore, I think it requires long time observation to determine the effect.” [51]

Inaccurate knowledge about how vaccines work also fueled some of the wariness and skepticism [54,115]:

“[T]he same concerns I have with any vaccine is... you’re getting the virus, it’s a very weak virus but you’re still getting the virus and you’re taking the risk that... maybe if the vaccine that you’re getting is not as weak, like the virus as weak as it should be, then maybe you’re more susceptible to actually like breaking out and getting the STD. But also just HPV, it seemed really hastened... When it came out for everyone to get it and it didn’t seem like it was very tested to me.” [54]

In one study involving UK participants, the change to quadrivalent vaccine led some participants who received the bivalent vaccine to believe they may not be fully protected because the bivalent vaccine was not as effective: “ It’s different now. It’s been researched and changed. [...]I hope that other girls aren’t thinking ‘Well I’m fine because I’ve got it [vaccination]” [115].

Finding 26. Pharmaceutical companies and business motive: Young adults expressed skepticism towards pharmaceutical companies and their motives, suggesting that public panic and greed may influence vaccination campaigns. Participants questioned the motive of vaccination promotion and who stood to most benefit [76,101]. Young adults also criticized the advertising tactics used for the vaccine suggesting campaigns may be manipulative or misleading by not adequately informing people about potential risks and benefits [62,88]; they also questioned who (e.g., drug companies vs the government) should be promoting the vaccine [51,76] and were critical of the marketing of the vaccine as a product [88,101].

“Well nowadays, whatever they offer me a vaccination against, a medicine, or whatever it is, and they tell me it is very good, I will always keep in mind who will win the most. Is it my health, is it this guy’s pocket, the government or state, or whoever it is, does not matter” [101]

“I think it [marketing campaign] was quite directed...which then to me I think that’s wrong, you shouldn’t be advertising, you know thinking about the audience like that because it’s not a product, it’s er.. medical, you’re not trying to sell this!” [88]

“... the government instead of the drug companies should take the role to promote (the vaccine)...If the drug companies take the initial role to promote, it could only promote through limited media sources... But if this is the government to take the role, the vaccine can be introduced in sex education.” [51]

Theme 9: Gendered Perceptions and Bias

Finding 27. Gendered perceptions of HPV risk: Many participants exhibit misconceptions about HPV being primarily a women’s disease. Some young adult men believed HPV does not affect men and that only women needed to be vaccinated because HPV affected them the most [45,60,66,69,80]. In some instances, men expressed knowing they could be carriers of HPV and pass it on to their (female) partners without themselves getting sick [58,60,69].

“I think the vaccine is for woman... I heard it’s only, the vaccine...no no, the virus only target woman, even if the man got it, it wouldn’t affect them. But he would be the carrier of that [virus], he might transmit that [virus] to his partner who is a female....” [69]

One study also demonstrated they gendered perception was not solely a male issue; a female participant also expressed no knowing men could get vaccinated [72]:

“I really didn’t know that men could get even the vaccine. My friend and I were talking about it. He’s like, “Yeah, I had Gardasil, too,” and I was like, “Really? You don’t have cervix. You’re a guy.” He was like, “It’s a vaccine for HPV.” I was like, “What?” It didn’t make sense to me at that time because I thought this vaccine is for women only.”

Finding 28. Gender biased promotion: The gendered marketing and promotion of HPV vaccines led to perceived unfairness in who gets access to vaccine and who is responsible for getting the vaccinated in the context of sexual health. Some young adults criticize the gendered nature of vaccination campaigns that were predominantly aimed at women, questioned the fairness of offering the vaccine primarily to girls and women and advocated for equal access to vaccination for all genders/sexes [58,62,81,113]:

“I’m really skeptical about the vaccine, particularly because it’s mass marketed towards girls and women and absolutely no focus on boys and men. And you know it’s a vaccine for HPV, it’s not a vaccine for cervical cancer even though the strains it targets can lead to cervical cancer. But I just feel that if we actually want to reduce cancer we probably should be vaccinating everyone. I think it is interesting that they’re targeting only girls and women because there hasn’t been any long-term research so we don’t really know what’s going to happen ten years down the line, 25 years down the line.” [113]

“I think the biggest thing is just letting [boys and men] know it’s an option because I, obviously, when I was 18 they didn’t tell me, so I didn’t get it. But the second I was told about it, I did. So, I think it’s just a matter of being aware that it exists.” [81]

Men and transgender individuals particularly noted the lack of representation and targeted advertising towards their demographic; this led to them feeling less informed about the risks and importance of vaccination [47,58,66,69]:

“It was that commercial. And I it stands out to me so much because I remember “HPV can lead to cervical cancer.” And I just remember hearing it and it stuck in my brain forever, and I just remember being like “Thank god I don’t have ovaries.” (I: Mhm.) But then I googled it one day cause I got, I was like “What if I get it one day” and I was like, “wait it can affect me too?” [69]

‘‘The biggest thing, again, was primarily marketed towards women, which - cisgender women - is, then, the question of, well, then, why did I bother, as a male? You know, as a cisgender male, it doesn’t make sense for me.” [47]

‘‘There is a misconception that if you’re a gay man, you don’t need to get it [HPV vaccine].“ [58]

A couple of studies revealed a discussion on the unequal distribution of responsibility for sexual health between genders, with some feeling that HPV vaccination campaigns unfairly target women and reinforce gender biases. Young adult women raised concerns about the stigmatization of women’s sexuality and the unequal burden of responsibility placed on them in sexual relationships, being a “scapegoat” of men’s sexual risk-taking behavior [77,113]:

“Ita: It sends a message that it’s a girl’s responsibility. It’s a girl’s responsibility to be on the pill and its just perpetuating that. When I was a teenager it was always the girls responsibility to carry a condom, it wasn’t for boys to worry about. Boys need to be responsible for their sexual health too.

Anna: Yeah, straight men may get reassurance from the fact that their partner has had the vaccine so they cannot catch it.” [77]

“Okay, so I have a problem with the vaccine even though I got it. The way it’s being marketed towards girls stigmatizes girls’ and women’s sexualities as being the source of the problem. Just like when you look at, on having responsible protective sex, again a lot of the onus is put on girls to be sort of the arbitrators of sexuality so that they have to monitor their partner’s behaviour and make sure to take on that responsibility of being responsible for both her and her partner without attributing very much responsibility to the man who is involved in the sexual relationship.” [113]

Theme 10: Government and policy

Finding 29. The government’s involvement and role (or lack thereof) in HPV vaccination promotion were influential in vaccine decision-making. For some young adults, the government’s involvement in and approval of the HPV vaccine was viewed as confirmation of its importance [48,96]:

“Well that kind of reassures you as well. If the government is making sure you have those jabs and they’re paying £400 for you to have them, then it does work and it helps people…” [96]

“For me, if the government thinks that it’s important enough for you to use your CPF [Central Provident Fund] money for it or even Medisave money for it then it must be important enough. Enough important [to be] on the radar for them. I mean you won’t see them [government] giving flu vaccination and tapping from Medisave right?” [48]

Conversely, lack of government involvement in HPV vaccine promotion raised questions among participants [52,88]: “Well, for me the primary reason is that, in reality, if the government wanted to support this thing, it would have provided more information, as a first step towards action” [88]. Similarly, mistrust in the government led some participants to be critical of government initiatives: “For Natives, vaccinations are crazy. The whole history with the IHS (Indian Health Service), I’m not sure people believe they can trust them[the government]’‘ [65].

SEM Categorization of findings

To enhance our understanding of the factors that influence young adult vaccination decision-making and uptake, we organized our review findings across the domains of the socioecological model (SEM). The SEM proposes an interplay and interdependence of factors within and across different ecological levels that influence health behaviors [117]. We acknowledge that not all findings neatly fit into the constructs of the SEM and that some findings may span multiple domains–we placed findings in ecological levels that was most representative of their level of influence as presented by the data (Fig 2).