Factors influencing adolescent girls’ decision in initiation for human papillomavirus vaccination: a cross-sectional study in Hong Kong

Cervical cancer is the fourth commonest cancer among women worldwide with estimated 528,000 new cases in 2012 [1], and the eleventh commonest cause of cancer-related death among women in Hong Kong (HK) in 2011 [2]. Virtually all cervical cancers are caused by persistent infection with human papillomavirus (HPV), particularly HPV types 16 and 18. HPV vaccine is highly effective in preventing persistent HPV infection and precancerous cervical cancer caused by HPV-16 and HPV-18 among females not yet infected at the time of vaccination [3, 4]. The cumulative lifetime risk of infection can be greater than 75% for one or more genital HPV infection [5]. In Hong Kong, about 10% of young women (under 26 years old) were HPV positive [6]. Recent study in Macao (neighbouring city of Hong Kong) showed higher prevalence of HPV infection and the most prevalent genotypes were found to be similar to those in south-west and southern China [7]. There has been increasing rates of cervical cancer among younger generation in China and also leading causes of premature death among women in south Asia, [8], prevention is an important public health issue so study on the drivers and barriers to HPV vaccination is very much needed [9].

Studies conducted during the early phase of introduction of vaccine including studies conducted in HK among Chinese girls attending secondary school (age 12–19), revealed that intention to be vaccinated depended on understanding of HPV being the causative agent, safety and efficacy of vaccination, perceived seriousness of HPV infection, the cost of the vaccine, and recommendation by general practitioners (GPs) or significant others such as family members [10–13]. Systematic review conducted in Australia covering studies from 2006 to 2011 highlighted the importance of correct information by a reliable source such as health care providers and higher vaccine uptake rate by school based vaccination [14]. The authors called for more studies from a boarder range of developed and developing countries. However, very few studies had targeted Chinese population. Although only 15% of women living in metropolitan and rural regions of China had heard of HPV vaccine, they were willing to be vaccinated if available [15]. Study among university students in HK (mean age 19.4 ± SD 1.0 years) has shown that sexually active participants of the study reported greater interest in HPV vaccination [16]. Sexual openness amongst Chinese adolescents has increased during recent years [17]. The first peak of cervical cancer has been shown at age 40 which suggested that females in Hong Kong would be infected by HPV during early 20s [18]. As immune response to HPV vaccination is higher in younger subjects [19], we need to examine the determinant factors for initiation of HPV vaccine of this age group.

Currently in Hong Kong, HPV vaccination is not included in government vaccination programme (quadrivalent vaccine was first licensed in Hong Kong) so recipients are required to pay about HK$3,000 (US$1 = HK$7.8) to complete the 3 doses from GPs privately. The GDP per capita in Hong Kong is comparable to USA (US$36,667 and US$49,922, respectively, according to International Monetary Union, 2012). The Centre for Health Protection of Department of Health has issued guidelines for cervical cancer prevention covering cervical cancer screening and HPV vaccine, However many factors such as cost, understanding and attitude towards cervical cancer can affect adolescent girls’ decision of receiving HPV vaccination. Study in 2010 revealed that only 11% of girls had intention to have vaccination. This study aimed to update the potential factors influencing the initiation of HPV vaccination among Chinese adolescent girls in HK without universal coverage. The findings would enlighten future strategy to improve the vaccine uptake rate with cost being a barrier. Although the uptake of HPV vaccine might be influenced by socio-cultural context, the results of this study will be useful not only for Asian countries and also other countries without full coverage of vaccination.

This study provided updated information on the uptake rate of HPV vaccination in Hong Kong, knowledge and attitude of adolescent girls towards cervical cancer prevention, as well as the drivers and barriers to HPV vaccination. The findings would be useful for the development of future strategies to improve vaccine uptake rate. The uptake rate of HPV vaccination was low with over half of the respondents in pre-contemplation and contemplation stage, and there was a knowledge gap on cervical cancer prevention. Knowledge scores, reasonable cost of vaccination, parents’ education level, family income, comments from friends and relatives, perception of cancer being horrifying disease, and knowing more about the linkage of HPV infection to cancer prevention were found to be significant factors for initiation of vaccine by uni-variate analysis. Multivariate analysis identified three independent significant factors associated with initiation of vaccine: perception of cancer as terrifying disease, school should provide more information on cancer prevention and comments from relatives and friends having received the vaccine.

Social norm and social influences and also self-perceived susceptibility were the main determinant factors for initiation of HPV vaccination as reflected by reporting the importance of parental support, recommendation from doctors, having all females to receive the vaccine, and high likelihood of developing cervical cancer, which are similar to findings in previous studies conducted locally and overseas [11–14]. However, adolescent girls reported that the main channels of information were from media and very few received information from schools or parents which could possibly be one of the contributing factors for the low HPV uptake rate. Those in contemplation and pre-contemplation stages perceived fewer benefits and more harms towards HPV vaccination as reflected by their own values and external factors such as influence from significant others and social norms [20–22]. Channel of information from media would become a source of social influence so it would also make a change to the knowledge of cervical cancer prevention. Although study findings revealed an overwhelming desire for more information on cervical cancer prevention by the respondents and their reported willingness to change their lifestyles for prevention, they did not receive much information and offer of HPV vaccination services in clinical setting so the uptake rate remained low (Figure 1). If the adolescent health providers could discuss disease prevention and side effects of vaccination, the uptake rate would be improved as reflected by a recent survey conducted amongst parents and adolescents aged 15 to 17 in a county of New York [24].

Multivariate analysis identified three important independent factors associated with initiation of vaccination (Table 5). As the actual uptake rate of vaccination was low among respondents and also among female population in Asia [25], comments from close friends and relatives became a strong driving force to parents’ decision and also the significant source of information regarding benefits and side effects of vaccination which explained why it was found to be a significant independent factor. A recent qualitative study in HK [26] revealed lack of recommendations from health care providers so comments from friends and close relatives would then become critical. The active involvement of GPs and other health professionals in cervical cancer prevention would help to build up a critical mass of population with a more positive attitude towards HPV vaccine. This would have significant impact on their close friends and relatives by sparking off the cascade effect.

Reinforcement of vaccination through social network was also found to have core influence on parental support for vaccination when challenged by anti-vaccination messages [27]. Mothers used a simple risk and benefit equation when they encountered ‘anti-vaccination’ messages, so advocacy for vaccination should involve stories about people benefited from vaccine-preventable diseases [28]. This would explain why the perception of cancer as terrifying disease turned out to be the independent significant factor. In one UK study, it was found that mothers with experience of cancer in the family were more likely to accept HPV vaccination for their pre-pubertal daughters [29].

To facilitate the initiation of HPV vaccine among students, schools should provide information and this factor is independent significant factor for initiation of HPV vaccination. Many studies have shown the effectiveness of school based health promotion in improving health behaviours of student [14, 30, 31]. Hong Kong has established a good infrastructure of ‘Health Promoting School’ based on WHO standard and has demonstrated the effectiveness of health improvement among student [31]. Schools in Hong Kong do not have school nurses to deliver information on effective cervical cancer prevention. If school staff can be equipped with appropriate knowledge, they are the potential health advocates whom students would turn to for information [32]. In HK, there is room to equip the knowledge of epidemiology of HPV infection and skills in motivating for behaviours change among GPs [33]. Systematic reviews have revealed higher acceptance of HPV vaccine among parents and young adults who believed that their physicians would recommend [14, 34, 35]. The local GPs are the potential source of information on health issues, and would improve the health literacy of both students and family members based on the conceptual model of health literacy at risk [36].

There were some of limitations of the current study that should be acknowledged. Firstly, the participating schools were not recruited based on random sampling but the sample size was larger than other related studies in Hong Kong. Table 1 shows how our sample population compared with Hong Kong population. Our sample consisted of higher proportion of girls aged 19 or above still in secondary school. The sample population had lower proportion of parents with post-secondary school education and income above US$3,750. Our study captured those with family income between US$1,250 to US$3,750 (above poverty line and below median level), and also those students from schools willing to participate in cervical cancer prevention program and the sample was not skewed towards higher socio-economic class. Many studies on this topic used convenient sampling method [17] with very few studies of sample size over 1,000 on Chinese female adolescents. Secondly, a cross sectional study would only identify associating factors rather than causative factors. Future study has been planned to follow up the vaccination behavior. Thirdly, variables reflecting demographic, family and personal factors were found to have higher percentage of missing data. This might have some effect on the statistical power in demonstrating significant difference. There were some missing data in some questions but the numbers were small (less than 20 questionnaires). The demographics (including parents’ working status, parents’ education level and family income) between the participants who answered and did not answer three of the particular questions (ever heard of cervical cancer, ever heard of HPV vaccine and intention for vaccination) were compared with no statistical difference (P above 0.5), indicating low likelihood of responding bias.

The classes of S6 and S7 were smaller which would introduce a selection bias in the older age group. Sub-analysis of differences in knowledge scores and demographic factors between students of S6 to S7 and S2 to S5 was performed with no statistical significance. Sexual activities were not recorded as schools did not want possible misconception of implication of HPV vaccine to early sexual activity.

Public education on cervical cancer needs to be well penetrated in the community as comments from relatives and friends play a significant role in influencing initiation of vaccine. If the adolescents do not agree that cancer as terrifying disease, they are unlikely to consider HPV vaccine to prevent cervical cancer. School as setting to provide source of information would be one strategy to facilitate uptake rate of HPV vaccine as students have expressed their wishes that school should provide more information on prevention of cancer. The young girls need to understand the pathogenesis of cervical cancer better and assess their own risks based on credible sources, so they have better perception of seriousness of the disease.