A total of 3110 participants were selected and contacted. 1071 did not answer and 555 refused participation, which translates into a response rate of 47.7%. After exclusion of unanswered and the invalid surveys, (n = 79) 1405 surveys were considered valid for the analysis (1116 online and 289 paper-based) (see reasons of invalid surveys in Additional file 1: Figure S2).

Sociodemographic characteristics

Most of the recruitment sites were public (68.0%) and were located in a region considered as low VCR (55.9%) (Table 1). Distribution according to gender and age was similar in each stratification group.

Table 1 Setting and socio-demographics profile of respondents

Most respondents were mothers (86.2%), between 40 and 49 years (69.1%), with a university degree (35.6%), in full-time employment (61.8%), living in a place with more than 50,000 inhabitants (37.0%), of Spanish nationality (97.4%), married (81.7%), with 2 children (63.1%) and not vaccinated against HPV (76.6%). Only 7.6% of the parents stated that they had been vaccinated against HPV, and 15.8% of them were unsure of their vaccination status (Table 1). Of the children about whom the survey was completed, 736 (52.4%) were girls with a mean age of 11.5 (SD: 1.6) years. Eight hundred and ninety-five (63.7%) of the children had not been vaccinated against HPV and 391 (27.8%) had. For the rest, the vaccination status was reported as “unknown”.

HPV knowledge

The majority of the respondents (90.7%) had heard of HPV infection. The pediatrician (44.8%) was the most common source of information, followed by family and friends (40.4%) and the Internet (39.3%).

The participants had a medium-to-high degree of HPV knowledge, with a mean score of 28.9 out of 40 (95% CI 28.7–29.2). Additional data are provided in the Additional file 1: Figure S3 and S4. In general, the parents agreed that HPV was a serious health problem (39.9% strongly agree, 53.1% agree) and that it was one of the most common sexually transmitted diseases (17.9% strongly agree, 52.2% agree).

The respondents correctly answered that HPV is a sexually transmitted disease (89.2%), although 10.8% were not sure how it is transmitted (Additional file 1: Figure S5). Most of the parents considered than women (89.2%) or girls (69.1%) could get infected by HPV. In contrast, only 50.2% and 67.2% considered that boys and men could be infected, respectively (data not shown). Regarding possible diseases related to HPV infection, the majority of the respondents considered HPV infection to be related to cervical cancer (73.7%). However, in Fig. 1 it is shown that parents were less aware of the role of HPV in other diseases.

Fig. 1

In terms of HPV prevention; most of the parents answered that it could be prevented by the HPV vaccine (87.2%) and condom use (80.9%). A lower proportion stated that delayed sexual debut (10.2%), personal hygiene (13.9%) and monogamy (14.2%) were also reported mechanisms for preventing HPV infections. Seven percent were not sure how to prevent this infection (data not shown). Additional data are provided in the Additional file 1: Figure S5.

In order to obtain more information about HPV infection, most parents would rather consult healthcare professionals such as pediatricians (80.1%), family doctors (68.3%) and gynecologists (78.1%). Only 19.8% of the respondents would consult the Internet or the social media (Data not shown).

HPV vaccine acceptability

The respondents had a medium-to-high degree of HPV vaccine acceptability, translating into a mean score of 3.37 out of 5 (95% CI 3.30–3.44) (Additional file 1: Figure S3).

In general, the participants presented a high level of agreement (strongly agree + agree) in considering that HPV vaccination is necessary in girls and boys. However, the results revealed that a higher proportion of parents considered it necessary in girls compared to boys (Fig. 2 and Additional file 1: S8).

Fig. 2

Answers to question: “I would vaccinate my son/daugther against HPV”

The main reasons for having the child vaccinated were to protect them against sexually transmitted diseases (67.4%) or against cancer and/or genital warts (77.4%), whereas the reasons for not having them vaccinated included lack of information (27.9%), fear of possible adverse events (20.9%) and other unspecified reasons (29.3%) (Additional file 1: Figure S7).

With regard to the type of information needed for the HPV vaccination to be acceptable for parents who initially disagreed to vaccinate their daughter/son: 55.7% would request information about vaccine safety; 54.5% would need a doctor’s recommendation, 51.8% about HPV vaccine efficacy, 49% about the HPV vaccine in general and 46.1% about HPV infection (Data not shown).

The proportion of parents that would consult a pediatrician to obtain further information about the HPV vaccine represented 93.6% (Fig. 3).

Fig. 3

Main sources to be consulted for obtaining more information about HPV vaccine, according to participant’s opinion

Knowledge of HPV vaccination

The parents evinced an intermediate-to-high degree of knowledge of HPV vaccination, with a mean score of 15.5 out of 21 (95% CI 15.3–15.6) (Additional file 1: Figure S3 and S4).

As it was observed with HPV infection, 92.1% of the respondents had heard of the HPV vaccine, the main source of information being the pediatrician (62.3%). Family and friends (34.5%), the gynecologist (27.8%) and the Internet (25.1%) were also mentioned as sources of information about the HPV vaccination.

Only 57.5% of the participants provided a correct answer indicating that the HPV vaccine was funded only for girls, whereas up to 25.1% of the parents did not know if the HPV vaccine was funded as part of the Spanish vaccination program (data not shown).

When the parents were questioned about the recommended age for vaccination, most of them answered correctly, with a mean (SD) reported age of 12.10 (1.21) years.

As occurred with HPV infection, 90.8% and 55.2% of the parents knew that girls and women, respectively, can be vaccinated against HPV. In contrast, the proportion of participants that considered that male populations could be eligible for the HPV vaccine was lower: only 60.1% and 37.9% of the parents considered that boys and men, respectively, could be vaccinated (Data not shown).

Up to 75.9% of the parents concurred (strongly agree + agree) in considering the HPV vaccine as effective, and 76.8% agreed that its benefits outweigh the risks. Nevertheless, it is important to point out that nearly 20% of the parents opined that they lacked sufficient information to answer (data not shown).

The HPV vaccine results tallied with the answers in the HPV knowledge section, HPV-related diseases. Thus, 80.0% of the participants considered that cervical cancer could be prevented with the vaccine, although the percentage was much lower for other diseases, such as genitals warts or anal cancer, that also affect males (Fig. 4). Additional data are shown in Additional file 1: Figure S6.

Fig. 4

Diseases that can be prevented by HPV vaccination, according to participant’s opinion

Knowledge and acceptability of vaccines in general

Knowledge and acceptability of vaccines was high, 6.6 out of 10 (95% CI 6.4–6.8). In fact, 25.8% of the participants obtained the maximum score (10 points).

More details are included in Additional file 1: Figure S9.

Correlations

There were significant and positive correlations between all variables (vaccine knowledge, HPV vaccine knowledge and HPV vaccine acceptability), and parents who scored high in one variable tended to score high in the other variables (Fig. 5).

Fig. 5

Correlations between knowledge and vaccine acceptability. p < 0.001 for all correlations. The colour intensity and shape indicate the strength of the correlation

The highest correlation was observed between HPV knowledge and HPV vaccine knowledge (0.7), followed by the correlation between HPV vaccination knowledge and HPV vaccine acceptability (0.4). Lower correlations were observed between other pairs of variables, although they were statistically significant (Fig. 5).

Typologies of respondents

The results of the LCA analysis allowed us to conclude that there were 4 groups of parents, according to different response patterns:

Class 1 (the probability of belonging to this group was 0.47): they consider that vaccines are useful, effective, beneficial and also that parents who do not have their children vaccinated put other people at risk. On the other hand, they think that both girls and boys should be vaccinated and that their doctor has recommended such vaccination. This group of parents showed a high agreement in considering HPV as a sexually transmitted disease and a serious health problem.

Class 2 (probability: 0.34): they consider that vaccines may be useful, effective, beneficial and also that parents who do not have their children vaccinated put other people at risk but that they may need more information. They think that it might be necessary to have both girls and boys vaccinated and that their doctor has recommended such vaccination. This group of parents agreed in considering HPV as a sexually transmitted disease and a serious health problem. Although these parents may have their sons vaccinated, they may need further information about HPV or its vaccine.

Class 3 (probability: 0.15): this group of parents are very unsure or lack sufficient information about HPV and its vaccine. While they are not afraid of having their child vaccinated, this lack of information could increase their indecision.

Class 4 (probability: 0.04): this group of parents have a higher probability of not accepting the vaccine as they believed that vaccines are not useful, are not safe and are ineffective. In addition, they did not regard HPV as a common sexually transmitted disease and a serious health problem. Furthermore, they tended to think that there is no need to have boys and girls vaccinated. In this group of parents, a high proportion stated that their doctor did not recommend the HPV vaccine.