Table 3.

Description of the main findings assessed from the studies included in the systematic review

Study	Geographic area	Country	Vaccine	Outcome category
				1. Vaccine-related issues (knowledge about the disease and the vaccine, vaccines’ effectiveness and safety)	2. Vaccination-related issues (source of information, vaccine costs, vaccination setting, injection fear and related pain)	3.Individual factors	4. Socio-cultural-economic characteristics
Nabirye et al 2020	Africa	Uganda	HPV	- Lack of awareness was the main reason given by 45% of the adolescents for not receiving the vaccine - Factors that positively influenced uptake of the vaccine: receiving an explanation for possible HPV vaccine side effects	- Not aware of the number of doses that they must receive and others were not aware of the schedule or interval of the vaccines. - Reluctance to vaccinate, being afraid of vaccines, and myths about the vaccines. - Factors that positively influenced uptake of the vaccine: having many options from where to get the vaccine.	Not applicable	Not applicable
Choi et al 2013	Asia	Hong Kong	HPV	Not applicable	- Among schoolgirls who had not been vaccinated, 27.1% expressed willingness to be vaccinated at market price, 26.5% not willing to be vaccinated because the market price was too high, 46.4% not willing to be vaccinated for reason other than vaccine cost.	Not applicable	- The high price of HPV vaccines is a major barrier to vaccine acceptability
Wang et al 2016	Oceania	Australia	All	- Among the respondents: 64.1% strongly believed that vaccines were beneficial; 24.7% responded “moderately” beneficial; 6.4% “slightly” beneficial; 4.8% disagreeing or uncertain.	- Adolescents were less likely than adults to seek information about vaccination from media sources, and were more likely to seek information from social networks including families and schools	- Adolescents were more likely to prefer a joint decision with parents about vaccinations or to make a decision on their own.	Not applicable
Griffin et al 2018	America	USA	All	- A little over half 56% of participants reported that they felt sufficiently informed about vaccines and their safety. - The possible side effects of vaccines is a potential driver of vaccine hesitancy among a subset of adolescents.	- Almost half 47% of adolescents reported family physicians or other medical professionals as their primary source of vaccine information, followed by their parents/guardians 38%. - The most trusted source of information was family physician or other medical profession while the least trusted source for information about vaccines was social media.		Not applicable
Read et al 2010		USA	HPV	- Less than half 44.5% of respondents were interested in receiving the HPV vaccine, while the remainder were either uninterested 15.2% or unsure 40.2%. - Not knowing enough about the vaccine because the vaccine is too new was the main reason cited by the sample of adolescent girls 40% for not being interested in receiving the HPV vaccine. - Regarding attitudes, 41.3% of adolescents had a very favorable attitude by responding 9 or 10 toward the utility of vaccines in preventing diseases.	Not applicable	- Among respondents 47.2% believed that adolescents should make vaccination decisions for themselves. – Additionally, 31.4% of adolescent girls were not interested in receiving the HPV vaccine because they believed they were too young to think about or to have sex.	- Knowledge was significantly higher in those who had at least one graduated parent, those who had received information about the vaccines from physicians and those who needed additional information about the vaccines.
Herman et al 2019		USA	All+ Focus on HPV	- Boys were significantly more likely than girls to perceive vaccines to be very safe (48.4% vs 30.2%, p < .01) and very effective (49.7% vs 29.0%, p < .01).	Not applicable	- Approximately 1/3 of adolescents reported having a say in the decision to be vaccinated and 1/4 of students expressed a desire for specific information about vaccines.	- Adolescents in non-urban areas of Upstate New York were generally marginalized in the vaccine decision-making process
Khuranaa et al 2015		USA	HPV	- Vaccine acceptance was low among adolescent males (and their parents), and the majority of participants were uncertain if they wanted the vaccine - Boys who were unsure about wanting the vaccine indicated they would like to get the vaccine if it protected against genital warts (60%) or against cervical cancer in women (65%).	Not applicable	- History of sexual activity were associated with greater odds of acceptance for a vaccine against genital warts and only knowing someone who had received the vaccine was a significant predictor of conditional acceptance for a vaccine protecting females against cervical cancer	- Asian race was associated with lower odds of conditional acceptance compared with Caucasian race (p < .001) - Income >$75,000 was associated with higher odds of conditional acceptance of a vaccine against genital warts compared with income less than or equal to $75,000 (p = .011).
Caskey et al 2017		USA	HPV	Not applicable	- Older respondents were more likely to report cost as a barrier to vaccine receipt, compared to younger respondents. - More than 80% of respondents would be likely to receive the vaccine if recommended by a healthcare provider or parent, compared to 55%if close friends received the vaccine - Of those who reported a healthcare visit during the 6 months prior to the survey, just 1/3 reported that their healthcare provider had ever discussed HPV or the HPV vaccine.	- Among respondents 1/3 reported not being sexually active or concerns about vaccine safety as the most important reasons for foregoing vaccination. - Younger respondents were more likely to report lack of sexual activity as the reason for not receiving the vaccine, compared to older respondents	Not applicable
Pennella et al 2020		USA	HPV	- Among respondents 87% indicated that the HPV vaccination was a prevention measure; 52% spoke specifically of prevention of HPV transmission. - Students inquiries were mostly centered on HPV vaccine composition, administration, duration and how the vaccine interacts with the body.	- Among respondents 87% indicated that there was no concern around the HPV vaccine and that the HPV vaccine is good and helpful.	Not applicable	Not applicable
Lavelle et al 2019		USA	All+ Focus on HPV	- More likely to choose vaccines with 99% effectiveness than vaccines with 20%. - Vaccine effectiveness of 70% or 95% effectiveness did not impact adolescent choice.	- Adolescents are most sensitive to Primary Care Physicians recommendation, and out-of-pocket cost for vaccination in their decision to get vaccinated.	Not applicable	Not applicable
Kreidl et al 2020	Europe	Austria	All	- Lack of awareness: only 1/3 of participants knew about their right to decide to get vaccinated at age 14 and that they could chose to be vaccinated over parental objections. - Those who consider measles and HPV severe diseases had a significantly higher intention to be vaccinated - The level of knowledge about vaccine-preventable diseases is pretty scarce in the region	Not applicable	Not applicable	Not applicable
Costantino et al 2020		Italy	HPV	- Better attitudes and knowledge regarding HPV infection and vaccination are attributable to the formative role of families and schools. - Students that had previously received information about sexual transmitted diseases at home or at school showed statistically significantly higher knowledge scores on HPV than others.	- Parental awareness represented one of the main factors influencing the acceptance of the HPV vaccine among preadolescents, and was associated with the quantity and quality of information provided on HPV at school	Not applicable	Not applicable
Pelucchi et al 2010		Italy	HPV	- Both students and parents seem to underestimate the likelihood of HPV infection, and this is associated with a lower propensity for vaccination.	Not applicable	- Females more than males were aware that HPV infection could concern themselves and would undergo vaccination against HPV. - The students who were aware that HPV infection could affect themselves were more in favor of HPV vaccination, regardless of whether they were male or female.	Not applicable
Stocker et al 2013		Germany	HPV	- Reasons for being HPV-unvaccinated reported: concerns about side-effects 30.8% -concerns specifically about HPV vaccine safety -female students appeared to be more knowledgeable in terms of transmission of HPV than male students	-Among respondents 2/3 reported that the vaccination is too time consuming	- Reasons for being HPV-unvaccinated reported: Dissuasion from parents (40.2%), dissuasion from their physician (18.5%)	Not applicable
Huon et al 2020		France	HPV	- Lack of information among boys and their parents about HPV and its vaccination. - The probability of being amenable to being vaccinated was significantly higher when the children were worried about the consequences of being infected, and perceived that there was a risk of HPV infection, that the vaccine could be effective and protect against serious disease.	Children generally go along with their parent’s choice.	Not applicable	- The were not significant associations between the age of the children (p = .412), attending middle or high school (p = .176), being at a private or public facility, the socio-professional category of the parents (p = .105), living in an urban versus a rural area (p = .298), and the presence of a general practitioner in the town where they resided (p = .184), and the children’s favorable attitude toward HPV vaccination.
Maier et al 2015		Romania	HPV	- A very small proportion had heard of HPV infection, HPV vaccine and Papanicolau smear test, that is, 20.22%, 67.92% and 22.9%, respectively. - The most common reason for not receiving the HPV vaccine was the lack of information 80.6% followed by parents’ concerns regarding safety 11%, fear of pain 5.59% and not being sexually active 2.7%. - Among participants, 97.7% of the respondents declared interest in receiving more information about HPV.	Not applicable	Not applicable	- Monthly household income over 1000 euros and self-perceived good relationship with family members were statistically associated on a multivariate logistic regression analysis with a high HPV knowledge score and rate of vaccination.
Marshall et al 2019		Ireland	HPV	- Adolescents demonstrated poor knowledge and understanding of HPV, HPV-related diseases and/or the HPV vaccine. - Vaccination was viewed as an accepted norm, and participants recognized the importance and benefits of immunization.	- Adolescents discussed their fear of needles, fear of cancer, fear of vaccine side-effects and fear of the unknown; their fears did not discourage vaccination. - Expressed the view that the vaccine would not be offered free of charge if it was unsafe or ineffective.	- Participants relied on their parent/guardian to provide information and make healthcare decisions on their behalf.	Not applicable
Hilton et al 2013		Scotland	All	- Awareness of HPV infection (Girls were most aware of HPV infection but it was nonetheless subject to misunderstandings; boys commonly believed it to only affect girls, and both sexes demonstrated confusion about its relationship with cervical cancer) - Enthusiastic at the prospect of more vaccines becoming available for their age group	- Combined vaccines are preferred since they reduce the overall number of injections needed - Immunization in school were not always positive	Not applicable	Not applicable
Pelullo et al 2018		Italy	All	- Attitudes: 41.3% of adolescents had a very favorable attitude assessing the utility of vaccines in preventing diseases	Not applicable	- Regarding vaccination decisions, 47.2% believed that adolescents should make vaccination decisions for themselves	- Knowledge was significantly higher in those who had at least one graduated parent

The results were grouped into four different outcome categories: 1. Vaccine (knowledge of technology/disease, effectiveness, safety, side effects); 2. Vaccination (source of information, costs, setting, fears, pain); 3. Individual factors; 4. Socio-cultural-economic implications.