Mothers’ preferences and willingness to pay for HPV vaccines in Vinh Long Province, Vietnam

Social Science & Medicine 73 (2011) 226e234

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Social Science & Medicine journal homepage: www.elsevier.com/locate/socscimed

Mothers’ preferences and willingness to pay for HPV vaccines in Vinh Long Province, Vietnam Christine Poulos a, *, Jui-Chen Yang a, Carol Levin b, Hoang Van Minh c, Kim Bao Giang c, Diep Nguyen d a

RTI International, Health Preference Assessment, USA PATH, USA c Hanoi Medical University, Viet Nam d PATH, Viet Nam b

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 12 June 2011

About 530,000 women develop cervical cancer worldwide and 275,000 die from the disease each year. Eighty percent of these deaths occur in developing countries. In Vietnam, cervical cancer has recently emerged as the most common type of cancer in women, and there are no national screening programs for cervical cancer. Since 2009, two different human papillomavirus (HPV) vaccines have been licensed for use in Vietnam, but access to these vaccines is generally limited to people who live in urban areas. Studies have shown that HPV vaccination may be cost-effective in cervical cancer prevention in Vietnam, depending on vaccination costs. Given that current HPV vaccines are expensive and public health funding for supporting a rapid introduction of the vaccine is limited, expanding and sustaining access to the HPV vaccine may require alternative financing mechanisms, such as fees-based immunization services. A conjoint analysis study was conducted with mothers of girls 9e17 years of age in Vinh Long Province in Vietnam to estimate the mothers’ demand for HPV vaccines for their daughters and to measure the tradeoffs between vaccine fees and vaccine uptake. The results suggest that the demand for HPV vaccines was high, increased with vaccine effectiveness and duration of effectiveness, and decreased with vaccine cost. Vaccine effectiveness was the most important vaccine attribute to these mothers, followed by duration of effectiveness. The predicted probability of respondents buying an HPV vaccine that was 70% effective for 10 years varied by the price, ranging from 30% when the vaccine price was $353 per course, to 68% when the vaccine cost $6 per course. As expected, demand and predicted purchase probability were higher among groups with higher socioeconomic status. Ó 2011 Elsevier Ltd. All rights reserved.

Keywords: Conjoint analysis Vietnam Human papillomavirus (HPV) Vaccine Willingness to pay Demand Cervical cancer

Introduction Every year, about 530,000 women around the world are diagnosed with cervical cancer and about 275,000 women die from the disease (Ferlay et al., 2010). Globally, cervical cancer is the second most common cancer in women, and the incidence rate in less developed regions (17.8 cases per 100,000) is more than double the incidence rate in more developed areas (9.0 cases per 100,000) (Ferlay et al., 2010). In Vietnam, it is the most common cancer among women, where about 5000 women are diagnosed and 2500 die each year (Ferlay et al., 2010). While cervical cancer screening programs have been effective in reducing cervical cancer incidence in developed countries, cervical cancer prevention in Vietnam has largely relied on opportunistic screening with low levels of coverage (J.J. Kim et al., 2008). * Corresponding author. Tel.: þ1 3153784843. E-mail address: [email protected] (C. Poulos). 0277-9536/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.socscimed.2011.05.029

New vaccines against human papillomavirus (HPV) could prevent as much as 70% of all cervical cancer cases (Goldie et al., 2008). GlaxoSmithKlines’s bivalent HPV vaccine and Merck & Co., Inc.’s quadrivalent HPV vaccine are both licensed in Vietnam. The vaccines are highly effective in preventing persistent HPV infection and the subsequent precancerous lesions due to infection with two types of HPV (known as types 16 and 18). Both types cause about 70% of cervical cancer worldwide. Because the vaccines are not effective once a woman has been infected, and acquisition of HPV infection occurs relatively quickly after sexual debut, it is widely accepted that providing young adolescent girls with the vaccine before the onset of sexual activity will be the most cost-effective strategy (World Health Organization, 2009). Although J.J. Kim et al.’s (2008) cost-effectiveness analysis suggests that population-based HPV immunization can be costeffective, this depends on vaccine price and coverage, and the availability of preventive screening. Vaccine price and coverage will be affected by vaccine financing. The Vietnamese government is

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unlikely to be able to afford the implementation of a large-scale HPV immunization program due to health budget constraints and competing health priorities. While the GAVI Alliance identified the HPV vaccine as part of a package of priority vaccines for future GAVI support in 2008, resource constraints are likely to limit a full-scale introduction of the HPV vaccine before 2015. Given that HPV vaccines are more expensive than many other vaccines and would be added to strained government health budgets, a financially sustainable HPV vaccine delivery strategy is likely to require user financing. In recent years, the government of Vietnam has introduced fee-based services to improve revenue flows at the provincial government level. While all children under 6 years of age are exempted from fees for vaccines offered by the national immunization program, a number of vaccines for children over 6 years of age are currently offered for a fee (covering the cost of the vaccine and vaccine administration). Some of the vaccines offered for a fee include rubella, Haemophilus influenzae type b (Hib), hepatitis B (HepB), pneumococcal disease, rotavirus, pentavalent vaccines (Diphtheria-Tetanus-Pertussis [DTP]-Hib-HepB), quadrivalent vaccines (DTP-HepB), and influenza. However, the viability of fees as a financing mechanism for HPV vaccines depends on private demand for vaccines. In particular, how would vaccine coverage vary with changes in vaccine fees, vaccine characteristics, and family economic status? In Vietnam, except for a few districts that are participating in a special pilot project, access to HPV vaccines is presently limited to relatively affluent households living in urban areas where feebased immunization services are available through public and private health facilities. At the time of the study (February through March 2009), the prices of these vaccines ranged from US$120 to nearly $360 for three doses of vaccine (the range had narrowed to $120 to $200 by October 2009). As a consequence of the limited availability and high prices, there is almost no information on the demand for HPV vaccines in the general population. To address this information gap, PATH commissioned a study to assess the willingness to pay (WTP) for vaccines using a choiceformat conjoint analysis (CA) study. The study also estimates the tradeoffs mothers are willing to make between vaccine fees, vaccine effectiveness, and duration of effectiveness, and measures vaccine coverage for given vaccine features. The results from this analysis can help assess whether fee-based HPV immunization services are a feasible way to achieve reduced morbidity, reduced mortality, and financial sustainability. This information can be useful for targeting immunization programs and it can also inform the content of information and education programs to promote interest in, and demand for, HPV vaccines.

Methods CA methods recognize that goods, including vaccines, have value because of their characteristics or attributes. Individuals have preferences for each attribute and are willing to accept tradeoffs among different attributes. CA methods examine these tradeoffs to assess the weights people assign to various attributes. Analysts have used CA methods to quantify preferences and WTP for a variety of market and nonmarket goods and services. In addition to a long history of market-research applications, researchers have adapted these techniques to evaluate public health interventions and pharmaceutical treatments (e.g., Brown, Finkelstein, Brown, Buchner, & Johnson, 2009; Johnson et al., 2006, 2009; Ryan, 1999). CA methods have recently been applied to measure the demand for vaccines (Brown, Johnson, Poulos, & Messonnier, 2010; Cook, Whittington, Canh, Johnson, & Nyamete, 2007; Sur, Cook, Chatterjee, Deen, & Whittington, 2007).

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Survey The first draft of the survey instrument was informed by qualitative formative research conducted in Vietnam (Nguyen et al., 2010), previous research on HPV vaccines, and collaborators familiar with local conditions. This draft was refined based on 25 in-depth, one-onone interviews. As part of the 7-day enumerator training in general survey methods and specific training on administering the choice questions, enumerators pretested the survey by interviewing 50 mothers. The final household survey (available from the authors) had six sections. The first section introduced the purpose of the survey and sought consent for the interview. The second section guided the interviewer in the selection of a daughter between the ages of 9 and 17 years of age if there were multiple daughters in the household. The respondent was asked to consider this girl when answering all of the vaccine choice questions. The third section measured perceptions, knowledge and experience with gynecological services, cancer, cervical cancer, genital warts, HPV, and vaccines (including the HPV vaccine). The fourth section was the stated preference section, described in detail below. The fifth section collected demographic and socioeconomic information, including respondents’ time preferences. The sixth section measured the interviewer’s assessment of the quality of the interview. The module on preferences for the HPV vaccine began by describing HPV infections and their consequences to ensure that all respondents had the same information. Respondents were told that new vaccines may be available in their community in the future. The features, or attributes, of these vaccines were described one by one to the respondent (Table 1). The selection of attributes was informed by previous findings on vaccine characteristics that were important to mothers (Brown et al., 2010; Cook et al., 2007; Nguyen et al., 2010; Sur et al., 2007). The attribute levels were selected to encompass both the relevant range of clinical outcomes and the full range over which respondents are likely to have well-defined preferences based on the in-depth interviews and pretests. Vaccine effectiveness was described as the joint probability of being exposed to an infectious agent and being protected by a vaccine. The explanation (Suraratdecha, Ainsworth, Tangcharoensathien, & Whittington, 2005) relied on pictures with blue and red figures representing persons who were and were not protected against cervical cancer (Fig. 1). Respondents’ understanding of vaccine effectiveness was tested before the choice questions. Respondents were then told that each vaccine would require administering 3 shots over six months, that re-vaccination (at additional cost) would be required to restore protection if the effectiveness wore off, that all vaccines were safe (possibly causing only soreness or swelling at the injection site) and of good quality, and that vaccines would all be available at the district hospital and other health facilities near the district hospital. The survey also explained that the Table 1 Vaccine attributes and levels. Vaccine attributes

Levels

Vaccine effectiveness in reducing cervical cancer risk

50% risk reduction 70% risk reduction 99% risk reduction

Duration of vaccine effectiveness

2 Years 10 Years Lifetime

Vaccine cost for 3 doses of vaccinea

US$6 (100,000 Vietnamese Dong) US$29 (500,000 Vietnamese Dong) US$118 (2,000,000 Vietnamese Dong) US$353 (6,000,000 Vietnamese Dong)

a At the time of the survey, the exchange rate was 17,000 Vietnamese dong ¼ 1 US dollar.

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Fig. 1. Example choice question.

vaccine cost would be paid over a 6 month period, though no further details were provided. Respondents were reminded of their budget constraint before answering the choice questions. The variant of CA used in this study involves asking respondents to complete several choice questions, each with two alternative vaccine profiles that vary in terms of their characteristics or attributes (Louviere, Hensher, & Swait, 2000). (Fig. 1) A discrete choice elicitation question asked respondents to indicate which of the two vaccines they would purchase for the “focal daughter” at this time. The enumerator recorded which of the vaccines the respondent preferred, or if the respondent would prefer to not purchase either vaccine. The “neither” option allowed us to examine whether households were “in the market” for HPV vaccines. A household was in the market if the respondent would purchase the vaccine if it were available to them at an acceptable price. It was out of the market if they would not purchase the vaccine at any price. If respondents chose “neither” for all the choice questions, they were asked why they would not purchase any vaccines, then were asked if they would get the vaccine for their daughter if it were free. If the answer the latter question was no, they were “out of the market.” The attribute levels in each choice question varied according to an experimental design that was constructed using a variation of a commonly used algorithm (Huber & Zwerina, 1996; Kanninen, 2002; Zwerina, Huber, & Kuhfeld, 1996). The experimental design comprised 36 questions. The pretest and pilot survey results indicated that respondents could respond to up to six choice questions without being fatigued or losing interest. Thus, 6 versions of the survey, each with 6 questions, were created and one version was randomly assigned to each respondent. Research ethics The research design and procedures were approved by RTI’s Institutional Review Board and PATH’s Research Ethics Committee. The study secured verbal informed consent from each respondent.

country, it was outside of the area where an HPV vaccination demonstration project was being implemented (Nguyen et al., 2010), and HPV vaccines were not available to the study population. Vinh Long Province is located approximately 135 km from Ho Chi Minh City. The province has about 1500 square kilometers and a population of about 1 million people, of which only 14% live in urban areas. Annual household income in Vinh Long is about US$ 2800 (General Statistics Office of Vietnam, 2006). In the Mekong Delta region, 88% of females and 94% of males are literate, 11% never attended school, 33% attended primary school, 7% completed secondary school, and 2% completed university (General Statistics Office of Vietnam, 2006). Forty-five percent of people are selfemployed farmers, 11% are farm laborers, 22% are self-employed in other sectors, and 22% are non-farm wage laborers (General Statistics Office of Vietnam, 2006). A multistage sampling strategy was employed. Given the effort required to develop a sampling frame for this study, the study selected one of Vinh Long’s seven districts to work in. Tam Binh District was selected to capture variation in accessibility (i.e., roads and terrain) and distance to urban areas that typically have better access to health care. Seven rural communes and two urban wards were randomly selected from the district. A comprehensive list of households with at least one girl aged 9e17 years was assembled for the selected communes and wards, from which households were randomly drawn. In the last stage, respondents and daughters were selected. Respondents were mothers who had at least one daughter aged 9e17 years. If there was more than one daughter aged 9e17 years, a focal daughter, who would be the subject of the vaccine choice questions, was selected using a random number table. Randomization was used to neutralize bias that may be introduced if mothers were to select the focal daughter and to ensure variation in the characteristics that may affect preferences (e.g., daughter’s age and birth order). One-third of the sample was drawn from urban areas, which represents an oversample of the urban residents. Data collection

Study area and sampling The study area was the Vinh Long Province in the Mekong Delta region of Vietnam. This southern province was selected because its incidence of cervical cancer was higher than other parts of the

The survey was administered to a sample of 300 mothers between March 3 and 15, 2009. Data from the paper questionnaires were transferred into a Microsoft Access file using codes designed during survey development and implementation and using

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established methods for quality assurance checks (Munoz, 2005). All data analysis was conducted using STATA statistical software (version 10).

Results The average study respondent was 42 years old and had 4 persons in her household (Table 2). Most respondents (88%) only had one daughter between 9 and 17 years of age. The average age of the focal daughter in the survey was about 14 years. The mothers were literate and educated, which was consistent with the education rates in the 2006 (General Statistics Office of Vietnam, 2006) for females aged 40e44 years. Of the 300 respondents, nearly three-quarters (74%) could read, more than one-third completed primary school (36%), about one-third completed secondary school (27%), and almost 16% completed high school. Only 5% of respondents never attended school. The majority of households (78%) had a male head of household.

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Half of the respondents (54%) were farmers or fishermen. Since incomes were difficult to measure accurately, we relied on a series of variables to gauge socioeconomic status, including housing, expenses, asset ownership, and indebtedness. Almost all (98%) households lived in homes that they owned or were owned by a family member, and the majority of sample households (72%) owned their own fields. Households also had good access to some infrastructure services. Nearly all homes (99%) had electricity and used it (98%) for lighting, and almost three-quarters (73%) of households had a phone. While the majority of the households collected drinking water from rivers and streams (about 58%) and had no adequate sanitation (about 78%), few relied on networked water and sanitation infrastructure. Household ownership of consumer durable goods was high, with the majority of respondents owning goods such as clocks (86%), bicycles (92%), televisions (93%), and motorcycles (about 59%). Fewer households reported owning goods such as a radio (about 38%), sewing machine (about 35%), or refrigerator (29%). Health perceptions and experience

Table 2 Description of survey respondents. Demographic and socioeconomic characteristics

Overall (N ¼ 299)

Urban (n ¼ 100)

Rural (n ¼ 199)

Respondent characteristics Mean age (years) Mean years of education Never attended school (%) Did not finish primary school (%) Primary school (%) Secondary school (%) High school or higher (%)

42.0 7.1 4.7 15.7 36.3 27.0 15.7

41.9 7.9 2.0 10.0 34.0 31.0 22.0

42.1 6.7 6.0 18.5 37.5 25.0 12.5

Read newspapers Can easily read (%) Can read with difficulty (%) Cannot read at all (%)

74.0 19.0 6.7

82.0 14.0 4.0

70.0 21.5 8.0

Occupation Farmer/fisherman (%) Business owner (%) Housewife (%) Manual labor (%)

54.2 17.1 14.1 12.0

38.0 27.0 22.0 1.0

62.3 12.1 10.1 13.1

Household characteristics % male-headed households Mean household size (# of persons) Vietnamese (Kinh) ethnicity (%)

78.3 4.4 99.3

80.0 4.4 100.0

77.4 4.3 99.0

Religion Ancestor worship (%) Buddhist (%) Catholic (%) No religion (%)

63.3 26.0 2.7 7.0

67.0 25.0 2.0 5.0

61.5 26.5 3.0 8.0

Home ownership Owned by family member (%) Owned by extended family member (%)

83.0 14.7

84.0 14.0

82.5 15.0

Main source of drinking water Water piped into residence/plot (%) Well into residence/plot (%) River/stream (%) Pond/lake (%) Rain water (%)

24.4 7.4 57.5 2.0 3.0

52.0 3.0 42.0 0.0 1.0

10.6 9.6 65.3 3.0 4.0

Main sanitation facility No facility (%) Flush toilet (%)

77.6 21.7

63.0 35.0

84.9 15.1

Fuel for lighting Electricity (%) Kerosene (%) Phone ownership (%) Health insurance (%)

98.0 1.7 73.0 93.3

99.0 1.0 79.0 91.0

97.5 2.0 70.0 94.5

In general, respondents were familiar with vaccines. Seventynine percent had heard of vaccines, and nearly all of these respondents understood that vaccines prevent disease. Of the respondents who had heard of vaccines (n ¼ 236), only half (53%) had paid for a vaccines for either an adult or child. While the majority of respondents (83%) had had a gynecological exam, few were familiar with preventive screening for cervical cancer. Only 13% of respondents had heard of a Pap smear and only 12% (n ¼ 35) reported having ever had a test for early detection of cancer. Further, most of the respondents who said they had had a test had not heard of Pap smears (24 out of 35). Most respondents were familiar with cervical cancer (85%) and about one-third (31%) reported knowing women who had cervical cancer, though none reported that it was caused by HPV infection and many respondents (67%) did not correctly identify its causes. All but one of the respondents familiar with cervical cancer reported that they thought it is a serious disease. Fifty-seven percent of respondents who had heard of cervical cancer thought it could be prevented and 50% thought it could be treated. Twenty percent of respondents had heard about a vaccine to prevent cervical cancer via advertisements on television (37%), news media stories (33%), friends or neighbors (25%), and doctors or nurses (12%). Only 2 respondents stated that someone they knew had received an HPV vaccine. Ninety-five percent of respondents reported that they were concerned about their daughter getting cervical cancer during their lifetime. Household preferences for the HPV vaccine After collecting data on health perceptions and experience, the survey described HPV infections and their consequences. Respondents were told that one-third of girls will have an HPV infection at some point and most infections resolve without treatment. They were also told that 2% of women in Vietnam will get cervical cancer in their lifetime, that early detection and treatment may prevent cervical cancer, and that cervical cancer is often fatal without early detection and treatment. The majority of all respondents were engaged and understood the choice exercise presented to them. Almost all (94%) of respondents understood the concept of vaccine effectiveness after it was explained to them once. Only 1 respondent did not understand effectiveness when it was explained a second time. Only 4% always chose “neither” or “don’t know/not sure.” Of these 11 respondents, 9 said they had no money for the vaccine, 1 said she

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was afraid the vaccine was not safe, and 1 did not answer the question. Nine of these 11 respondents would get the vaccine if they could get it for free. The study included several tests to examine the quality of respondents’ responses to choice questions. First, the survey included a choice task in which one vaccine was superior to the other in all attributes. The majority of respondents (84%) chose the superior vaccine in this question. To assess the consistency of respondents’ choices, one choice task was repeated. Fifty-six households (19% of the sample) failed this consistency test. Finally, we also examined whether respondents had dominant preferences for one or more attributes. We defined dominant preferences as always choosing the alternative with the better level of a single attribute. Sixty-three respondents (21%) had dominant preferences for risk reduction, 14 respondents (5%) had dominant preferences for duration of protection, and 105 respondents (35%) had dominant preferences for vaccine cost. While there is no single way to identify respondents with dominant preferences, the prevalence of dominant preferences in this study was comparable to the prevalence in other conjoint analysis studies in health (Propper, 1995; San Miguel, Ryan, & McIntosh, 2000; Scott, 2002). One possible explanation for these preferences is that these respondents simplify the tradeoff task by focusing on only one attribute, thus providing little or no information about their actual preferences. Another possible explanation is that these respondents have strong preferences for one attribute over the others; therefore, their responses are an accurate reflection of their preferences and the experimental design never offers a combination that is sufficiently attractive to induce them to trade away from the dominant attribute. These subjects presumably would make similar choices in selecting real vaccines, if possible. While we can identify subjects with dominant preferences, we cannot determine what motive led to the observed pattern of responses, so we do not exclude these observations from the analysis. In total, we excluded 42 respondents from the multivariate analysis of preferences for HPV vaccines (1 respondent who failed to understand vaccine effectiveness after two explanations, 11 respondents who were out of the market, and 30 respondents who always chose either Vaccine X or Vaccine Y). The final sample size for the analysis was 258. The analysis and interpretation of the discrete choice data are based on random utility theory (Louviere et al., 2000), which posits that respondents choose the alternative that provides them with the most satisfaction or utility. The choice data were analyzed using conditional logit regressions, which regressed the response to the choice question (e.g., Vaccine X, Vaccine Y, or neither) on the vaccine attributes and levels. The attribute levels were effects coded (Hensher, Shore, & Train, 2005), which allowed for nonlinear effects of different attribute levels on utility. We also used a robust variance estimator that accounts for clustering at the household and choice question levels. The parameter estimates from the conditional logit can be interpreted as preference weights that measure the effect of the attribute on utility when all other attributes are held constant. (The regression results are available in an online Appendix) A positive coefficient indicates that the corresponding attribute increases utility such that higher levels of that attribute (e.g., vaccine effectiveness) are preferred to lower levels of the same attribute. This also implies that higher levels of these attributes are associated with higher willingness to pay and higher purchase probabilities. Conversely, a negative coefficient indicates that the attribute generates negative utility such that lower levels of that attribute (e.g., lower costs) are preferred to higher levels. Thus, higher levels of these attributes are associated with lower willingness to pay and lower purchase probabilities.

Fig. 2 shows the rescaled preference weights for vaccine effectiveness and duration of effectiveness. The attribute level with the largest preference parameter (99% risk reduction) was assigned a preference weight of 10, and the attribute level with the smallest preference parameter (50% risk reduction) was assigned a preference weight of 0. The parameter estimates for other attribute levels were scaled relative to the largest and smallest parameter estimates. The vertical bars around each mean preference weight in Fig. 2 indicate the 95% confidence intervals for the weights. Attribute levels that were more preferred had higher preference weights than levels that were less preferred. These results indicate that changes in vaccine effectiveness had a greater effect on utility than changes in duration of effectiveness. This is shown by the fact that the utility of moving from 50% effectiveness to 99% effectiveness is greater than for any change between duration levels. For example, the difference in utility between 50% effectiveness and 99% effectiveness was about 3.4 times greater than the difference between a vaccine that is effective for two years and a vaccine that is effective for a lifetime. These results are consistent with the fact that more than one-half of respondents (57%) had an annual discount rate higher than 1500%. (The questions used to measure time preference are available in an online appendix). Respondents with such high discount rates would have discounted the future protection provided by vaccines, which would reduce the importance of duration of effectiveness. These results also show that the attributes are well-ordered, with better levels of each attribute providing more utility than less desirable attribute levels. The differences between preferences for adjacent levels for both vaccine effectiveness and duration were statistically significant (p-value < 0.05). The vertical distance between preference weights for the best level and worst level of an attribute can be interpreted as the overall relative importance of the attribute in this study. Vaccine effectiveness was the most important attribute to respondents, followed by duration of protection. Fig. 3 shows how the predicted choice probabilities increase with vaccine effectiveness and duration of effectiveness, and decrease with cost. For example, the probability of choosing a vaccine that was 70% effective and lasted a lifetime decreased from 74% when the vaccine was US$6 to 60% when the vaccine was US$29. At prices similar to current HPV vaccines in Vietnam, the probability of choosing a vaccine ranges from 46% (if the vaccine cost US$118) to 35% (if the vaccine cost US$353). The differences in these predicted choice probabilities are statistically significant (p-value < 0.05). Willingness to pay for the HPV vaccine The WTP results, calculated using the parameter estimates from the conditional logit model, are reported in Table 3. Empirically, the Preference weights 12 10 8 6 4 2 0 -2 99% risk reduction

70% risk reduction

50% risk reduction

Lifetime protection

Fig. 2. Rescaled preference weights.

10-yr protection

2-yr protection

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Uptake

99% risk reduction & lifetime protection 99% risk reduction & 10-yr protection

100%

70% risk reduction & lifetime protection 70% risk reduction & 10-yr protection

90%

50% risk reduction & 2-yr protection

80% 70% 60% 50% 40% 30% 20% 10%

US$ 0% 0

50

100

150

200

250

300

350

400

Fig. 3. Predicted choice probabilities for selected vaccines.

WTP for a specific vaccine is the utility that the respondent gets from that vaccine divided by the marginal utility of income, which is measured by the parameter on the HPV vaccine cost variable. The average maximum WTP is highest for the vaccine that is 99% effective for a lifetime ($356) and is statistically significantly different than WTP for vaccines with other levels of effectiveness (p-value < 0.05). The WTP for the most effective vaccine essentially reflects the private economic benefit of eliminating their daughter’s risk of cervical cancer. The WTP decreases with shorter durations of protection and lower vaccine effectiveness. Fig. 3 shows that the model predicts that about 30e35% of mothers would purchase a vaccine at the highest vaccine price in the study ($353), all else equal. Previous research suggests that prices levels in CA studies with three attributes and two alternatives should be set such that about 25% of subjects would select the alternative with the highest price (given other attribute levels) (Johnson, Kanninen, Bingham, & Özdemir, 2007). These predicted uptake results suggest that, despite careful pretesting, the highest price in the study may have been set a bit too low. When the highest price is too low, the tails of the distribution of estimated WTP are larger and WTP estimates are inflated. While predicted uptake at the highest price is likely to be overestimated, the accuracy of predicted uptake at lower prices is unlikely to be affected. Given this issue, we focus on the predicted choice probability in the remainder of the paper and discuss these results further in the discussion section. Preferences for the HPV vaccine by economic status Given the challenges of measuring wealth, we estimated an asset index to proxy wealth following Filmer and Pritchett (2001). Table 3 Average maximum WTP for HPV vaccines (in US$), by vaccine characteristics. Vaccine effectiveness

Duration of protectiona 2 Years

10 Years

Lifetime

50%

101 [96,105]

118 [113,123]

144 [138,150]

70%

163 [157,169]

185 [179,191]

218 [211,225]

290 [282,298]

318 [310,326]

356 [347,364]

99%

WTP ¼ willingness to pay. a The 95% confidence intervals shown in brackets indicate that average maximum WTP values for all of the HPV vaccines are significantly different from one another at the 5% level.

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We used principal components analysis to derive weights and construct a linear index from the data on asset ownership (Table 4). Because all the asset variables take only the values 0 or 1, the weights have an easy interpretation: a move from 0 to 1 changes the index by the weight (reported in the fifth column of Table 4). For example, a household that owns a motorcycle has an asset index higher by 0.136 than one that does not. Though we did not collect comprehensive expenditure data, we examined the correlation between monthly expenditures on utilities and health care and the asset index. The correlation is positive and statistically significant at less than the 1% level, but it is not very large (correlation coefficient is 0.28). Further, as asset index quintiles increase, so do respondent and household head level of education and literacy, and the number of assets owned. The asset index was used to categorize the households into three socioeconomic groups. The households with asset index values in the bottom 25% of the distribution were classified as “low income.” The middle 50% of the asset index distribution were “middle income” and the highest 25% percent were “high income.” The preference models were estimated separately by income group (the results are available in an online Appendix). Fig. 4 illustrates the relative importance of the attribute levels by asset group. For all asset groups, changes in effectiveness provided more value than changes in duration (that is, the lengths of the lines are longer). There is some evidence that vaccine effectiveness is a normal goodda good whose demand increases with income. While the utility of 50% and 99% effective vaccines was the same across groups, 70% effective vaccines provided the greatest utility to the highest asset group and the lowest utility to the lowest asset group. For all three asset groups, the preferences for vaccine effectiveness were well-ordered. Preferences for duration of Table 4 Scoring factors and summary statistics for variables entering the asset index. Asset

Own clock/watch Own bicycle Own radio Own television Own sewing machine Own motorcycle/scooter Own refrigerator Own car Use water from handpump or well Use surface water source Use other water source Own flush toilet Use other type of sanitation facility Have electricity Number of rooms Separate room for kitchen Use biomass for cooking fuel Dwelling made with all high quality materiala Dwelling made with all low quality materialb Own or lease  6 acres of land Asset Index

Scoring factor

Mean

SD

0.166 0.068 0.111 0.122 0.161 0.275 0.312 0.128 0.312

0.860 0.920 0.378 0.930 0.348 0.589 0.291 0.020 0.324

0.348 0.272 0.486 0.256 0.477 0.493 0.455 0.140 0.469

0.058 0.018 0.054 0.031 0.077 0.136 0.142 0.018 0.146

0.280 0.034 0.368 0.366

0.602 0.074 0.231 0.776

0.490 0.262 0.422 0.418

0.137 0.009 0.155 0.153

0.072 0.228 0.079 0.282 0.317

0.983 1.736 0.371 0.736 0.542

0.128 0.824 0.484 0.442 0.499

0.009 0.188 0.038 0.125 0.158

0.189

0.107

0.310

0.059

0.030

0.318 0

0.466 2.123

e

e

Weight in asset index (Scoring factor SD)

0.014

a High quality materials for floor include tiles, cement/concrete, stone, and brick. High quality materials for walls include cement/concrete, stone, and burnt bricks. High quality materials for roof include cement/concrete, metal, asbestos, burnt bricks, and tiles. b Low quality materials for floor include wood/bamboo and earth/mud. Low quality materials for walls include corrugated iron/metal/asbestos sheets, wood, raw bricks/mud, plastic/polythene and grass/thatch/bamboo. Low quality materials for roof include grass/thatch/bamboo.

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Preference weights

Low

Middle

High

14 12 10 8 6 4 2 0 -2 -4 99% risk reduction

70% risk reduction

50% risk reduction

Lifetime 10-yr 2-yr protection protection protection

Fig. 4. Rescaled preference weights, by asset group.

vaccine effectiveness were well-ordered for the lowest and middle asset groups, but they were not well-ordered for the highest asset group. The highest asset group, which had a higher percentage of respondents with annual discount rates more than 1500% than other asset groups, did not distinguish between the duration levels. Fig. 5 shows the predicted choice probabilities for a vaccine that is 70% effective for ten years by asset group. The highest asset group had the highest choice probabilities, followed by the middle and lowest asset groups, though most of these differences are not statistically significant. The graph does suggest that the lower asset groups were more sensitive to price than the highest asset group since the choice probabilities decreased more at higher prices for the former groups. (Average maximum WTP for all possible vaccines by asset group are shown in the online Appendix). Finally, we asked respondents who said they would choose an HPV vaccine for their daughter why they would want to get the vaccine. Most respondents (63%) stated that they would want to protect her from cancer. An additional 10% stated they wanted to ensure a healthy future for their daughter. Almost 20% reported that they thought the HPV vaccines in the survey were affordable. Discussion This paper describes a CA survey measuring Vietnamese mothers’ preferences for HPV vaccines for their daughters aged 9e17 years. Mothers preferred more effective vaccines that provided lifetime protection and demand decreased as vaccine cost increased. Effectiveness was a more important vaccine attribute, given the levels of effectiveness and duration in the study than the Uptake

Low Middle

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70% 60% 50% 40% 30% 20% 10% US$ 0% 0

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Fig. 5. Predicted choice probabilities for a vaccine that is 70% effective for ten years, by asset group.

duration of effectiveness. This ranking of attributes was consistent with the respondents’ high discount rates. These preferences were reflected in the sample average maximum WTP and predicted choice probabilities. While our estimates of mothers’ preferences may reflect the true value that mothers place on preventing cervical cancer in their daughters, there is also some possibility that these estimates are inflated due to validity threats and limitations of stated preference methods. The methods section described several measures (Whittington, 1998) to minimize validity threats, including hypothetical bias, strategic bias, enumerator bias, and yea-saying. Nevertheless, there are many factors that affect actual vaccine decision-making that were not included in this stated preference study. Thus, these findings should be considered suggestive rather than prescriptive when considering the effect of immunization program design (e.g., vaccine fees) on vaccine coverage rates. We assess the WTP estimates by comparing them to existing vaccine fees, estimates of WTP for other vaccines, and average household income in Vinh Long. In 2009, fees for selected vaccines in Vietnam ranged from $2 per dose of tetanus vaccines ($6 total) to $38 per dose of rotavirus vaccines (about $76 total). While these are not WTP estimates, they do indicate that average WTP for an HPV vaccine in our sample (which ranged from $101 to $356) was much higher than the fees parents have paid for other vaccines. The WTP estimates were also higher than WTP for typhoid fever and cholera vaccines measured in Vietnam, which ranged from about $0 to $10 depending on vaccine attributes (Cahn et al., 2006, D. Kim et al., 2008, and Cook et al., 2007). This may be partially accounted for by the fact that cancer in general is a dreaded disease and cervical cancer has higher case fatality rates (about 50% in Vietnam [Ferlay et al., 2010]) than either typhoid fever (about 1% [World Health Organization, 2007]) or cholera (less than 1% [Ryan et al., 2000]). These results are consistent with the fact that awareness and concern about cervical cancer was high in the study population (nearly all of the respondents were aware of cervical cancer and were concerned about their daughter getting cervical cancer) while much of the population had limited or no access to cervical cancer prevention (only 12% reported having ever had a test for early detection of cancer). Estimated WTP for HPV vaccines in our sample was much lower than in a US sample. Brown et al. (2010) estimated that mothers of girls aged 11e17 years were willing to pay an average of $663 for a 70% effective, 10-year vaccine (this vaccine also reduces the risk of genital warts by 90%dan attribute that was not included in our study in Vietnam), while our sample is willing to pay an average of $185 for a vaccine providing similar protection against cervical cancer. In this crude comparison, which does not account for important differences in price levels and substitute goods in these two populations, the relative size of the WTP estimates conforms to expectations. Using 2006 data on average annual per capita income in Vinh Long (General Statistics Office of Vietnam, 2006) (adjusted for inflation), average maximum WTP for the 50% effective vaccine represented 4e5% of annual household income, depending on the duration of effectiveness. The percentage increases to 10e13% for the 99% effective vaccine. Given that households in the Mekong Delta region spent 7.4% of their annual income on all health care in 2006 (General Statistics Office of Vietnam, 2006), the WTP estimates from this study do appear to be inflated. These comparisons provide some evidence that, despite the measures taken to minimize bias, WTP estimates from this study may be inflated. This may be due to the fact that the WTP results include the expected costs associated with getting to the district headquarters, where respondents were told the vaccine would be available. More importantly, this may be due to the fact that the

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highest price may have been set too low. While this limitation should be considered before using the WTP estimates in economic analyses, the more likely application of these study findings is in predicting uptake of the HPV vaccine at moderate fees. While predicted uptake may be inflated at higher prices, we believe that predicted uptake at low and moderate fees is accurate. HPV vaccines, which are expected to prevent approximately 70% of cervical cancer cases for 10 years or more, were being sold in urban areas in Vietnam for $120 to $360 for all three doses at the time of the study. On average, predicted choice probability for vaccines with similar characteristics ranged from 30% (for a 70% effective vaccine that would last 10 years and cost $353) to 39% (for a 70% effective vaccine that would last 10 years and cost $118). The results reported in the paper represent preferences among mothers in Vinh Long province, which is a typical province in Southern Vietnam, but likely does not represent mothers’ preferences in other parts of Vietnam with different socioeconomic and epidemiological characteristics. Overall, the predicted choice probability results suggest that extending access (by explicitly lowering cost or lowering implicit costs of access by expanding geographic coverage) to the vaccine would increase vaccine coverage. Predicted coverage would increase if costs were lower, and/or if vaccines were more effective and provided a longer duration of protection. While vaccine fees have a direct effect on access, the indirect costs of vaccination (including transportation and waiting) can be lowered by offering vaccines through sites that are more convenient. In follow-up questions about where the respondents would like to go to purchase the vaccine, 56% reported that they would want to get vaccine at the commune or ward health center, 38% said that they would like to get it at the hospital, and only 9% said that they would like to get the vaccine at home. The study results also indicate that demand, WTP, and predicted coverage increased with economic status. Thus, at a given vaccine cost, more girls would be vaccinated in higher economic groups than in lower economic groups. To achieve greater equity in vaccine coverage, immunization programs relying on vaccine fees may consider subsidies for lower income groups. The results also suggest that liquidity and access to credit may also increase demand. Three percent of respondents reported that they would borrow money to pay for HPV vaccines and these respondents were more likely to say they would purchase the vaccine. This suggests that allowing households to spread out payments for the HPV vaccine over time may increase vaccine coverage. Most of the sample (n ¼ 240) reported having access to one-month interest rates that ranged from 0 to 30% (average 2%; median 0%). While we measured mothers’ preferences for HPV vaccines for their daughters, the majority of respondents said that they would make the vaccination decision with another person. Nearly all of these mothers (94%) said that they would make the decision with their spouse. Only 28% of mothers said that they would make the decision alone. Respondents who reported that they would be the sole decision-maker were more likely to say that they would purchase the vaccine. While actual vaccine purchase decisions may differ from the stated choices of respondents provided during the interviews because of the influence of other household decisionmaker, the qualitative research conducted prior to the survey suggested that most mothers’ preferences for vaccines are influential in household vaccine decision-making. J.J. Kim et al. (2008) note that the cost-effectiveness of HPV immunization in Vietnam depends on vaccine price and coverage. The predicted uptake findings reported in this paper should be used to analyze the coverage and public health impacts of fee-based immunization services and vaccine features in expanded costeffectiveness analyses.

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