Most cervical cancers are caused by genital human papillomavirus (HPV). However, it can be prevented if females receive an HPV vaccine. Nevertheless, there is limited evidence of HPV vaccination and predictors of intention to obtain the vaccine among young women in Thailand. The paper aims to discuss this issue.
This cross-sectional study examined HPV vaccination and factors influencing intention to vaccinate among a convenient sample of college women in Thailand. The data collection was conducted via a self-administered “HPV and HPV vaccine-related knowledge, attitudes, and behaviors” questionnaire.
Out of 1,030 participants, 309 (30.0 percent) were aware of HPV and the HPV vaccine. Out of these, 257 participants reported that they had not obtained the vaccine and 18 participants were unsure if they had already obtained the vaccine or not. Only 34 participants confirmed that they had received the vaccine. Among those who were aware of HPV and the HPV vaccine, 56.4 percent of them did not know that most HPV-infected persons do not show any signs or symptoms, and 53.3 percent thought that the vaccine provided protection against other sexually transmitted infections as well. Most had positive attitudes toward vaccination and subjective norms. Among the participants who had not received the vaccine, the intention to obtain the vaccine was predicted by age, knowledge, attitudes toward vaccination, and subjective norms. The reasons for not being vaccinated included the cost of the vaccine, lack of knowledge, and perception of themselves being at low risk.
This study found low HPV vaccination among college women. However, those who had not received the vaccine intended to obtain the vaccine at some point in the future. An HPV vaccination campaign may be well tailored in order to increase the intention to obtain the vaccine which, in turn, may increase the HPV vaccination. Vaccination cost sharing should be discussed among Thai policy makers in order to alleviate the financial burden for women.
Ratanasiripong, N.T., Sri-Umporn, S., Kathalae, D., Hanklang, S. and Ratanasiripong, P. (2018), "Human papillomavirus (HPV) vaccination and factors related to intention to obtain the vaccine among young college women in Thailand", Journal of Health Research, Vol. 32 No. 2, pp. 142-151. https://doi.org/10.1108/JHR-01-2018-018
Emerald Publishing Limited
Copyright © 2018, Nop T. Ratanasiripong, Sirinat Sri-Umporn, Duangrat Kathalae, Suda Hanklang and Paul Ratanasiripong
Published in the Journal of Health Research. Published by Emerald Publishing Limited. This article is published under the Creative Commons Attribution (CC BY 4.0) licence. Anyone may reproduce, distribute, translate and create derivative works of this article (for both commercial & non-commercial purposes), subject to full attribution to the original publication and authors. The full terms of this licence may be seen at http://creativecommons.org/licences/by/4.0/legalcode
Genital human papillomavirus (HPV) is a globally common sexually transmitted infection (STI)[1, 2]. There are over 100 genital HPV types. Out of these, 13 types are identified as cancer-causing or high-risk HPV types. Among the high-risk HPV types, HPV type 6, 11, 16, and 18 are responsible for most genital warts and anogenital cancers, especially cervical cancer. Globally, cervical cancer remains amongst the top five of the most common cancers among women. Approximately 445,000 new cervical cancer cases were detected among women in developing countries in 2012, making up 84 percent of all cervical cancer cases in the world. In Thailand, cervical cancer was the number one killer among women for decades and has only been second to breast cancer after 2007. With a population of about 70 million in Thailand, there are approximately 6,300 new cases of cervical cancer with the death rate of 2,600 women each year – 7 Thai women die from cervical cancer each day.
The chance of being infected by genital HPV increases when the women are at a younger age, initiate sexual intercourse early, have multiple sexual partners, or have a partner who has multiple partners or an HPV infection, and do not use a condom[6-8]. Moreover, consistent condom use only provides 60 percent protection against HPV infection since HPV can be spread via unprotected skin-to-skin contact during sexual contact. Currently, no specific treatment for the HPV infection is available. The clinical standard suggests the routine use of a Papanicolaou (Pap) test to detect early precancerous cervical lesions. Cervical lesion treatment (e.g. cryotherapy, laser therapy, and conization) can then be applied in order to lessen the risk of such lesions to develop into invasive cervical cancer cells.
Encouragingly, the primary prevention method of HPV infection has become available through HPV vaccines. The Gardasil® vaccine was first recommended for female aged 9-26 in 2006. Thereafter, the Cervarix® vaccine was approved for female aged 10-25 in 2009. Since both HPV vaccines became available, the HPV vaccination rate has been increasing, especially in developed countries such as Australia, Canada, and the Netherlands. In the USA, national data in 2009 showed the vaccination coverage among adolescents was 44.3 percent and among women aged 19-26 was 17.1 percent. A 2012 study in the USA reported the HPV vaccination among young women aged 18-26 was 47.3 percent.
However, in Asia, there is limited literature on HPV promotion campaigns, vaccination uptake, and factors relating to the vaccination. Using the PubMed search engine with the keywords “HPV vaccination” followed by the country names in Asia produced limited literature between 2006 and 2015. In Singapore, out of 19 articles found, 2 articles discussed factors related to HPV vaccination among women aged between 18 and 49 years. In Japan, among 66 published articles, one study discussed HPV vaccination and its related factors among young women. In addition, an “HPV vaccination crisis” was reported due to controversies of the adverse effects of the vaccination, and the Japanese health officials took a negative position on HPV vaccination. In Thailand, out of 44 articles found, one study reported HPV vaccination intention and related factors. Since 2002, the Thai Government started to provide cervical screening to all women aged 35-60 years at five-year intervals. However, the Pap test has not been effectively used. Often, it is provided to the women on demand when the women already started to have signs and symptoms of cervical cancer. While Thailand has been trying to improve cervical cancer screening programs by using a dual-track strategy, i.e. using both Pap test and visual inspection to detect cervical cell abnormalities, Pap test screenings remain low (31-37 percent). Thus, it is imperative that primary prevention, by way of the HPV vaccination, should be promoted and adopted.
According to the theory of planned behavior, when a person has higher intention to engage in a behavior, the person has a higher chance to change the actual behavior. The intention to change a person’s behavior is directly influenced by the attitude toward such behavior, subjective norms, and perceived behavioral control. Knowledge, demographic, or personal history usually are indirect factors influencing the intention or behavior itself. By using this theory as a framework, this study examined the HPV vaccination and identified factors related to intention to obtain the vaccine among college women in Thailand. The study theoretical framework is shown in Figure 1.
This study was conducted with a convenience sample of young women from four public universities in Thailand in September-October 2015. The selected college women had to be between 18 and 26 years and willing to complete the study questionnaire. The maximum age was limited at 26 since the vaccine was recommended for women up to 26 years old. This study did not have any specific exclusion criteria.
Based on the study theoretical framework, the intention to obtain the vaccine might not be assessed unless the person was aware of HPV and the HPV vaccine. In favor of using a multiple regression analysis to determine the predictors of the intention to obtain the vaccine, the minimum sample size was calculated based on the established statistical parameters – a power of 0.9, small effect size (0.1), α equals 0.05, and three direct predictors (attitude toward obtaining the vaccine, subjective norm, and perceived behavioral control). The study needed at least 108 participants who were aware of HPV/the HPV vaccine and had not received the vaccine. When a pilot study was conducted, only 3 out of 15 women reported that they were aware of HPV/the HPV vaccine. In addition, since there was no published data on HPV/HPV vaccine awareness in Thailand, it was decided to seek at least 1,000 participants in order to ensure that the study obtained sufficient data.
The study was approved by the Institutional Research Board of California State University, Dominguez Hills, on May 28, 2015 (IRB No. 15-214). The researchers visited various classrooms and invited the students to complete the study questionnaire. The informed consent was placed as the first page of the questionnaire. When a student decided to participate and signed the consent, the researcher then collected the consent page and instructed the student to start completing the rest of the questionnaire. To encourage participation, each participant received 30 Baht cash (approximately US$ 1, the cost of a lunch meal at the university canteen).
The anonymous paper-based questionnaire titled HPV and HPV vaccine-related knowledge, attitudes, and behaviors was adapted and translated to Thai from the first author’s prior study with college women in the USA. The translated questionnaire was translated back by two persons – one researcher who earned her Doctorate Degree in nursing from the USA and one Thai-American citizen who earned her Master Degree in public administration. Both were fluent in Thai and English. The questionnaire consisted of HPV/HPV vaccine-related knowledge (eight true/false items), attitude toward obtaining an HPV vaccine (six semantic differential-scale items), subjective norm (five Likert-scale items), perceived behavioral control (four Likert-scale items), and intention to vaccinate (four Likert-scale items). Only the participants who had not been vaccinated answered the intention to vaccinate questions. The questionnaire was finalized after face validation was conducted with 15 college women. For Thai college women in this study, all scales had Cronbach’s coefficient αsbetween 0.69 to 0.91, except for the perceived behavioral control scale (0.45) which was excluded from further analysis.
Statistical Packet for the Social Sciences 22.0 was used for data analysis. Descriptive statistics were used to describe demographic and studied variables. Depending on the variables’ level of measurement, Spearman’s ρ, or Pearson correlation coefficients were utilized to examine the relationships between the participant characteristics, sexual history, indirect predictor (HPV knowledge), direct predictors (attitude toward obtaining the vaccine and subjective norm), and the outcome variable, intention to vaccinate. Hierarchical multiple regression was conducted by controlling significant indirect predictors (age, HPV knowledge).
The average age of the 1,030 female participants was 19.7 (SD=1.4). Most were Buddhist (94.9 percent). In total, 48.2 percent were in non-nursing major degree participants and 51.8 percent were nursing major students. For relationship and sexual-related history, 58.5 percent were single and 41.0 percent were dating. More than a half (63.9 percent) had initiated sexual intercourse; most of them (86.4 percent) had sex with males; and some (8.9 percent) had sex with both females and males. The average age of first sexual intercourse was 17.7 (SD=1.5, range 14-23). The average number of sexual partners in their lifetime was 1.8 (SD=1.7, range 1-19). Most never got tested for STIs (94.7 percent) and had never completed a Pap test (93.6 percent) (Table I).
Out of the 1,030 participants, 309 (30.0 percent) were aware of HPV and the HPV vaccine. A total of 257 participants reported that they had not obtained the vaccine, and 18 participants were unsure if they had already obtained the vaccine or not. Only 34 participants had already received the vaccine.
HPV/HPV vaccine knowledge
Among the 257 participants who had not received the vaccine (non-vaccinees), the mean HPV/HPV knowledge was 5.3 (SD=1.7, range 0-8). More than half did not know that most HPV-infected persons do not show any signs or symptoms (56.4 percent). Only 46.7 percent knew that the vaccine does not provide protection against other STIs (46.7 percent). However, most (90.3 percent) knew that HPV can cause cervical cancer and many (61.1 percent) knew that the HPV can cause genital warts (Table II).
Attitude toward obtaining the vaccine
The non-vaccinees had positive attitudes toward getting vaccinated against HPV (M=36.12, SD=5.6, with a possible range of 6-42). They believed that the HPV vaccination was good, useful, desirable, safe, favorable, and pleasant.
The non-vaccinees also had a positive subjective norm (M=17, SD=3.1, with a possible range of 5-25). Many (73.5 percent) strongly agreed or agreed that significant others would want them to get vaccinated. More than half (63.0 percent) also believed that their doctor would support them in getting the vaccine. However, many (84.4 percent) did not feel under social pressure to get vaccinated against HPV, and 64.5 percent of them did not believe that most women are getting vaccinated against HPV (Table III).
Intention to obtain the vaccine
Among the 257 non-vaccinees, the intention to obtain the vaccine was strong (M=15.6, SD=3.3, with possible range 4-20). Many strongly agreed or agreed with the statements “I intend to get vaccinated against HPV” (77.0 percent) and “I expected to get vaccinated against HPV at some point” (79.7 percent). More than half strongly agreed or agreed with the statements “I have decided to get vaccinated against HPV” (62.3 percent) and “I plan to get vaccinated against HPV” (59.3 percent).
Out of 1,030 participants, 34 participants had received the HPV vaccine. Presuming that the 721 participants who were not aware of HPV and the HPV vaccine have also not been vaccinated, the overall vaccination among young women in this study was 3.3 percent.
Predictors of intention to vaccinate among non-vaccinees
Vaccination intention was significantly positively correlated to two indirect predictors – age (r=0.20, p=0.01) and HPV/HPV vaccine knowledge (r=0.24, p<0.001). It was also positively associated with attitudes toward vaccination (r=0.50, p<0.001) and subjective norm (r=0.48, p<0.001). When age and HPV/HPV vaccine knowledge were entered in the hierarchical multiple regression model alone, they significantly predicted the vaccination intentio: F (2, 237)=10.8, p<0.001, adjusted R2=0.08. When attitudes toward vaccination and subjective norm were added, the prediction model of the entire group was significantly improved: F (4,235)=47.1, p<0.001, adjusted R2=0.44 (Table IV).
Among 257 non-vaccinees, 249 provided the reasons why they had not got the vaccine. Some provided more than one reason – resulting in 278 rationale instances in total. The top three reasons were cost of the vaccine (55.4 percent), lack of knowledge/need for more information about the virus, vaccine, vaccine side effects; where to get vaccinated (17.6 percent); and low-risk perception (13.3 percent; e.g. not having sex, having one partner, and not practicing risky sexual behaviors). Other reasons (14.4 percent) included that having the vaccination is not a priority, no interest, new vaccine suspicion, limited clinics offering the vaccine, questioning the vaccine effectiveness, and misunderstanding that Pap/HPV test was needed before vaccination.
Genital HPV can be easily contracted through skin-to-skin contact during sexual activity. A recently published study reported that approximately a quarter of Thai women aged 20-37 were infected with any HPV type, and 14 percent of the women were infected by a high-risk HPV type. The chance of getting infected also increases if the women initiate sexual intercourse at an earlier age and have multiple sexual partners[6, 23]. As Thailand has become more industrialized, the average age of first sexual intercourse has decreased from 20.5 in 2007 to 17.7 as the young women reported in this survey. This study also found that the average number of sexual partners in a lifetime was 1.75 by the time these women were in college. Most of these women also had not been tested for any STI including HPV and Pap test. Sadly, these factors will increase the chance of the young women contracting HPV and/or being diagnosed with cervical cell abnormalities in the future unless they complete a series of HPV vaccination.
This study found that HPV vaccination remains very low (3.3 percent) compared to a previous study published in 2012. This previous study conducted among a convenient sample of college women aged between 18 and 24 years found that only 1.2 percent of the participants received an HPV vaccine. The HPV vaccination in Thailand was also lower than in Singapore. A recent study conducted at a tertiary institution reported that 9.8 percent of Singaporean women aged between 15 and 22 years had received an HPV vaccine. A cross-sectional study conducted among medical and para-medical students in 2014 also showed better HPV vaccination rates in India; 6.8 percent of Indian college women and men had received the vaccine. At the global level, it is estimated that 39.7 percent of targeted women (between 9 and 45 years) have been vaccinated worldwide. HPV vaccination in Thailand has indeed fallen behind the international average.
Based on the theory of planned behavior, in order to increase HPV vaccination numbers, young women must have a high intention to obtain the vaccine. This study indicated that factors influencing intention include attitude toward obtaining the vaccine, subjective norm (perceived pressure from significant others in order to vaccinate), HPV/HPV vaccine knowledge, and age. Using the same theoretical framework, the study results are similar to prior studies conducted among young adults in Canada and America where the intention was predicted by the attitude and subjective norm[13, 28, 29]. In addition, a study conducted among Taiwanese undergraduate women reported that vaccination intention was associated with recommendations from others, vaccine cost, availability, and perceived disease severity, risks, and vaccination benefits. In Thailand, the quoted prior study found that the vaccination intention was predicted by recommendations from significant others, HPV knowledge, and perceptions of vaccination benefits and risks of contracting HPV. In terms of age, as young women get older and are exposed to more sexual health-related information, they may be more interested in receiving the vaccine.
In order to effectively lower the cervical cancer prevalence in Thailand, secondary prevention strategies (i.e. Pap test screening and early treatment of abnormal cervical cells) alone are not sufficient. Primary prevention through HPV vaccination is critically needed. With the goal to increase the HPV vaccination in mind, it is essential to set up HPV vaccination interventions which are well tailored for the young female population. Lastly, while the financial cost has been the major prohibitive factor to add the vaccine on the national vaccination program, more evidence has shown that the vaccine is cost effective compared to the cost of HPV and anogenital cancer treatments and damage to the quality of life[32, 33]. In Thailand, the series of HPV vaccines cost between US$ 180 and US$ 340, while the gross national income per capita was approximately US$ 3,900. Relieving financial burdens of vaccination is necessary. Vaccination cost must be discussed at the national policy level to alleviate the cost burden on young women or parents.
The study used a convenience-based sample. Generalizability cannot be applied to all Thai young college women. Reporting bias might have taken place if the college women had strong feelings toward HPV/the HPV vaccine. Recalling bias or errors might occur when the participants tried to recall their sexual history. Despite these limitations, the findings from this study suggest some ideas to set up HPV vaccination interventions including the following:
Conducting a national, promotional campaign to raise awareness of HPV and the HPV vaccine: even though HPV knowledge is not a direct predictor of intention or vaccination uptake, the knowledge will correct misperception or belief related to HPV, which, in turn, influences the attitude toward obtaining the vaccine. HPV knowledge topics may include HPV infection consequences as well as signs and symptoms. It will also be important to emphasize that persons infected by HPV may not manifest any signs and symptoms and can still spread the virus to sexual partners. In addition, information regarding HPV vaccine effectiveness, safety, and availability should be explained. Vitally, correction of misunderstanding that the vaccine provides protection against other STIs must be included in the awareness campaign.
Targeting the intervention toward both adolescent girls and young women: while it is recommended to vaccinate females once they enter adolescence and before they initiate sexual intercourse, young women in Thailand will still receive benefits from the vaccine since most of them started having sex later on at the age of 17-18.
|Age (n=1,024)||M=19.7 (SD=1.4)|
|Relationship status (n=1,028)|
|Ever having sex (n=1,028)|
|Age of first sex (n=365)||M=17.7 (SD=1.5)
|Number of sexual partners in lifetime (n=367)||M=1.8 (SD=1.7)
|Being tested for STI (n=365)|
|Having Pap test done (n=361)|
Notes: M, mean. A number of responses (n) differ because the participants chose not to answer or inadvertently skipped the questions
HPV/HPV vaccine knowledge: percentages of correct and incorrect/do not know answers
|Knowledge statements||Correct||Incorrect||Do not know|
|1. HPV can cause genital warts||61.1||10.9||28.0|
|2. HPV can cause cervical cancer||90.3||2.3||7.4|
|3. Most people with genital HPV have no visible signs or symptoms||43.6||31.5||24.9|
|4. Using a condom can provide partial protection against HPV||64.2||18.7||17.1|
|5. I can transmit HPV to my partner(s) even if I have no HPV symptoms||58.4||19.5||22.2|
|6. Only sexually active women should receive the HPV vaccine||75.9||9.7||14.4|
|7. Women who received HPV vaccine do not need to get routine Pap smear/test||84.4||3.9||11.7|
|8. HPV vaccine protects against all sexually transmitted infections||46.7||23.7||29.6|
Percentages of subjects who strongly agree/agree to HPV/HPV vaccine subjective norms statements
|Subjective norms statements||Strongly agree (%)||Agree (%)|
|1. Most people who are important to me think that I should get vaccinated against HPV||38.5||35.0|
|2. It is expected of me that I get vaccinated against HPV||15.6||30.4|
|3. I feel under social pressure to get vaccinated against HPV||3.9||11.7|
|4. My doctor would support my getting vaccinated against HPV||26.8||36.2|
|5. Most women like me are getting vaccinated against HPV||11.3||24.2|
Hierarchical multiple regression analysis summary for attitude toward HPV vaccination and subjective norms, controlling age and HPV knowledge, predicting intention to obtain HPV vaccine
|Attitude: getting vaccinated||0.24||0.03||0.40**|
Notes: n=240. *p<0.05; **p<0.01
1.Center for Disease Control, Prevention. HPV vaccines: vaccinating your pre-teen or teen. [updated: 2017 Jul; cited 2017 Aug 1]. Available from: www.cdc.gov/hpv/parents/vaccine.html
2.World Health Organization. Human papillomavirus and cervical cancer. [updated: 2016 Jun; cited 2017 Aug 1]. Available from: www.who.int/mediacentre/factsheets/fs380/en/
3.National Cancer Institute. Human papillomavirus (HPV) vaccines. [updated: 2016 Nov; cited 2017 Aug 1]. Available from: www.cancer.gov/about-cancer/causes-prevention/ risk/infectious-agents/hpv-vaccine-fact-sheet
4.World Health Organization. World cancer report 2014. [updated: 2017 Feb; cited 2017 Aug 1]. Available from: www.who.int/mediacentre/factsheets/fs297/en/
5.World Population Review. Thailand population 2014. [updated: 2016 Aug; cited 2017 Aug 1]. Available from: http://worldpopulationreview.com/countries/thailand-population/
6.Central of Disease Control, Prevention. HPV information for clinicians. [updated: 2017 Mar; cited 2017 Aug 1]. Available from: www.cdc.gov/hpv/hcp/index.html
7.Dunne EF, Unger ER, Sternberg M, McQuillan G, Swan DC, Patel SS, et al. Prevalence of HPV infection among females in the United States. JAMA. 2007 Feb; 297(8): 813-9, doi: 10.1001/ jama.297.8.813
8.Stanley M. Pathology, epidemiology of HPV infection in females. Gynecol Oncol. 2010 May; 117(S2): S5-10, doi: 10.1016/j.ygyno.2010.01.024
9.Winer RL, Lee SK, Hughes JP, Adam DE, Kiviat NB, Koutsky LA. Genital human papillomavirus infection: incidence and risk factors in a cohort of female university students. Am J Epidemiol. 2003 Feb; 1, 157(3): 218-26.
10.National Cancer Institute. Pap and HPV testing. [updated: 2014 Sep; cited 2017 Aug 1]. Available from: www.cancer.gov/cancertopics/factsheet/detection/Pap-test
11.Sheinfeld Gorin SN, Glenn BA, Perkins RB. The human papillomavirus (HPV) vaccine and cervical cancer: uptake and next steps. Adv Ther. 2011 Aug; 28(8): 615-39, doi: 10.1007/s12325-011-0045-x
12.Center for Disease Control, Prevention. Morbidity and mortality weekly report (MMWR): national, state, and local area vaccination coverage among adolescents aged 13-17 years – United States. 2009 [updated: 2010 Aug; cited 2017 Aug 1]. Available from: www.cdc.gov/mmwr/preview/mmwrhtml/mm5932a3.htm?s_cid=mm5932a3_e%0d%0a
13.Ratanasiripong NT, Cheng AL, Enriquez M. What college women know, think, and do about human papillomavirus (HPV) and HPV vaccine. Vaccine. 2013 Feb; 31(10): 1370-6, doi: 10.1016/j.vaccine.2013.01.001
14.Pitts M, Smith A, Croy S, Lyons A, Ryall R, Garland S, et al. Singaporean women’s knowledge of human papillomavirus (HPV) and attitudes toward HPV vaccination. Women Health. 2009 Jun, 49(4): 334-51, doi: 10.1080/03630240903158420
15.Sukegawa A, Ohshige K, Arai S, Sakanashi K, Usui M, Hirahara F, et al. Three-year questionnaire survey on human papillomavirus vaccination targeting new female college students. J Obstet Gynaecol Res. 2015 Jun, 41(1): 99-106, doi: 10.1111/jog.12500
16.Dornbusch HJ, Stiris T, Del Torso S, Ross-Russell R, Zavrsnik J, Wettergren B, et al. Human papillomavirus vaccination crisis in Japan. J Paediatr Child Health. 2015 Dec, 51(12): 1146-47, doi: 10.1111/jpc.13020
17.Juntasopeepun P, Davidson PM, Suwan N, Phianmongkhol Y, Srisomboon J. Human papillomavirus vaccination intention among young women in Thailand. Asian Pac J Cancer Prev. 2011; 12(12): 3213-9.
18.Sriamporn S, Khuhaprema T, Parkin M. Cervical cancer screening in Thailand: an overview. J Med Screen. 2006; 13(S1): S39-43.
19.Chalapati W and Chumworathayi B. Can a home-visit invitation increase Pap smear screening in Samliem, Khon Kaen, Thailand? Asian Pac J Cancer Prev. 2007 Jan-Mar; 8(1): 119-23.
20.Ajzen I. The theory of planned behavior. Organ Behav Hum Decis Process. 1991; 50(2), 179-211.
21.Ajzen I. Theory of planned behavior. [updated not indicated; cited 2017 Aug 1]. Available from: http://people.umass.edu/aizen/tpb.html
22.Faul F, Erdfelder E, Buchner A, Lang AG. Statistical power analyses using G*Power 3.1: tests for correlation and regression analyses. Behav Res Methods. 2009 Nov; 41(4): 1149-60, doi: 10.3758/brm.41.4.1149
23.Marks MA, Gupta S, Liaw KL, Tadesse A, Kim E, Phongnarisorn C, et al. Prevalence and correlates of HPV among women attending family-planning clinics in Thailand. BMC Infect Dis. 2015 Mar; 27, 15: 159, doi: 10.1186/s12879-015-0886-z
24.Chartsbin. Average of first sex by country. [updated: 2011; cited 2017 Aug 21]. Available from: http://chartsbin.com/view/xxj
25.Zhuang QY, Wong RX, Chen WM, Guo XX. Knowledge, attitudes and practices regarding human papillomavirus vaccination among young women attending a tertiary institution in Singapore. Singapore Med J. 2016 Jun; 57(6): 329-33, doi: 10.11622/smedj.2016108
26.Swarnapriya K, Kavitha D, Reddy GM. Knowledge, attitude and practices regarding HPV vaccination among medical and para medical in students, India a cross sectional study. Asian Pac J Cancer Prev. 2015; 16(18): 8473-7.
27.Bruni L, Diaz M, Barrionuevo-Rosas L, Herrero R, Bray F, Bosch FX, et al. Global estimates of human papillomavirus vaccination coverage by region and income level: a pooled analysis. Lancet Glob Health. 2016 Jul; 4(7): e453-63, doi: 10.1016/s2214-109x(16)30099-7
28.Fisher WA, Kohut T, Salisbury CM, Salvadori MI. Understanding human papillomavirus vaccination intentions: comparative utility of the theory of reasoned action and the theory of planned behavior in vaccine target age women and men. J Sex Med. 2013 Oct, 10(10): 2455-64, doi: 10.1111/jsm.12211
29.Ratanasiripong NT. Factors related to human papillomavirus (HPV) vaccination in college men. Public Health Nurs. 2015 Nov-Dec; 32(6): 645-53, doi: 10.1111/phn.12198
30.Hsu YY, Fetzer SJ, Hsu KF, Chang YY, Huang CP, Chou CY. Intention to obtain human papillomavirus vaccination among Taiwanese undergraduate women. Sex Transm Dis. 2009 Nov; 36(11): 686-92, doi: 10.1097/OLQ.0b013e3181ad28d3
31.Sajirawattanakul S, Sarnsamak P. Govt urged to drop HPV vaccine plan. [updated: 2012 Apr; cited 2017 Sep 22]. Available from: www.pressreader.com/thailand/the-nation/20120410/281861525482733
32.Termrungruanglert W, Havanond P, Khemapech N, Lertmaharit S, Pongpanich S, Khorprasert C, et al. Cost and effectiveness evaluation of prophylactic HPV vaccine in developing countries. Value Health. 2012 Jan-Feb; 15(S1): S29-34, doi: 10.1016/j.jval.2011.11.007
33.Jit M, Brisson M, Portnoy A, Hutubessy R. Cost-effectiveness of female human papillomavirus vaccination in 179 countries: a PRIME modelling study. Lancet Glob Health. 2014 Jul; 2(7): e406-14, doi: 10.1016/s2214-109x(14)70237-2
The authors declare no potential conflicts of interest with respect to the authorship, research, and/or publication of this paper. This research was supported by the Faculty Research and Creativity Activity Grant, California State University-Dominguez Hills, USA.