Mothers’ preferences and willingness to pay for vaccinating daughters against human papillomavirus

Abstract

A choice-format, conjoint-analysis survey was developed and fielded to estimate how features of human papillomavirus (HPV) vaccines affect mothers’ perceived benefit and stated vaccine uptake for daughters. Data were collected from a national sample of 307 U.S. mothers of girls aged 13–17 years who had not yet received an HPV vaccine. Preferences for four features of HPV vaccines were evaluated: protection against cervical cancer, protection against genital warts, duration of protection, and cost. We estimate that mean maximum willingness-to-pay (WTP)—an economic measure of the total benefits to consumers—for current HPV vaccine technology ranges between $560 and $660. All vaccine features were statistically significant determinants of WTP and uptake. Mothers were willing to pay $238 more for a vaccine that provides 90% protection for genital warts relative to a vaccine that provides no protection against warts. WTP for lifetime protection vs. 10 years protection was $245. Mothers strongly valued greater cervical cancer efficacy, with 100% protection against cervical cancers the most desired feature overall. Adding a second HPV vaccine choice to U.S. consumers’ alternatives is predicted to increase stated uptake by 16%. Several features were significantly associated with stated choices and uptake: age of mother, race/ethnicity, household income, and concern about HPV risks. These findings provide new data on how HPV vaccines are viewed and valued by mothers, and how uptake may change in the context of evolving vaccine technology and as new data are reported on duration and efficacy.

Introduction

Genital human papillomavirus (HPV) is the most prevalent sexually transmitted infection in the United States, affecting more than 25% of U.S. women aged 14–59 years in 2003–2004 [1]. Prevalence of HPV is highest among younger age groups and approaches 50% among sexually active 20 to 24-year-old women [1]. The more than 40 types of genital HPV are classified as either low-risk or high-risk types, depending on whether or not they are associated with cervical cancer [2]. High-risk HPV types cause virtually all cases of cervical cancer, and also may lead to anal, penile, vaginal, vulvar, oropharyngeal, and mouth cancers [3]. Low-risk HPV types may cause genital warts or recurrent respiratory papillomatosis.

The health and economic burden of HPV in the U.S. is substantial and is largely borne by women. In 2005, 11,999 U.S. women were diagnosed with cervical cancer and nearly 3924 deaths were caused by it [4]. Treatment of precancerous lesions, follow-up exams, and false-positive Pap tests incur significant financial and quality-of-life costs [5]. Prior to the use of HPV vaccines, direct medical costs from prevention and treatment of HPV-related genital warts and HPV-related cervical disease were estimated to be at least $4 billion per year [6], [7]. Worldwide impacts of HPV include over 274,000 cancer deaths per year [8]. Given the prevalence and burden of HPV, the public health benefits of HPV vaccines appear quite large. Yet, for the U.S. and other western countries, cost-effectiveness results are mixed. Routine HPV vaccination of pre-teen girls generally meets accepted thresholds for value, such as $50,000 or £30,000 per quality-adjusted life-year (QALY) [9], [10]. Catch-up vaccination of older girls is less cost-effective than routine vaccination of pre-teens [9], [11], and cost-effectiveness results are sensitive to duration of protection, vaccine coverage, and the types of HPV protected against.

Two prophylactic vaccines against HPV currently are in production, a quadrivalent vaccine (Gardasil^®, Merck & Co., Inc., Whitehouse Station, NJ, USA) and a bivalent vaccine (Cervarix™, GlaxoSmithKline Biologicals, Rixensart, Belgium). Both protect against high-risk HPV types 16 and 18, responsible for an estimated 70% of cervical cancers [12]. The quadrivalent vaccine also protects against low-risk HPV types 6 and 11, responsible for an estimated 90% of genital warts [13]. Both vaccines provide nearly 100% efficacy against pre-cancerous lesions associated with types 16/18 and may provide cross-protection against additional HPV types [14]. The duration of protection from both vaccines exceeds 5 years and continues to be assessed [15]. Additional vaccines, possibly with broader protection or other features, are in development [16], [17]. The bivalent vaccine does not protect against low-risk HPV types 6 and 11 but it has other features that may be important to consumers. It uses a new adjuvant [18], which is reported to generate a strong and sustained immune response [19], and it may have cross-protection against different high-risk types than the quadrivalent vaccine [14].

Both HPV vaccines are approved by the U.S. Food and Drug Administration (FDA), the quadrivalent in June 2006 and the bivalent in October 2009. Further, both are also recommended for routine vaccination in females aged 11–12 years (and for catch-up immunization for those aged 13–26 years) [2] by the Advisory Committee on Immunization Practices (ACIP). ACIP also approved resolutions to add both to the Vaccines for Children Program (VFC). Many private health insurance plans follow the same coverage. Recently released U.S. data for 2008 indicate that about 37% of girls aged 13–17 years had begun the HPV series [20].

Although cost-effectiveness studies of HPV vaccination can be an important tool for policymakers, cost-effectiveness studies do not account for consumer preferences [21]. Preferences of consumers do not necessarily align with those of policymakers or providers, who may have difference objectives. Cost-effectiveness studies also do not include the value of non-medical consumer benefits, such as “peace of mind,” risk aversion, and parent–child altruism, which may be important factors in vaccine uptake and acceptability [22]. To address these important factors, we developed a conjoint-analysis (CA) survey to provide new data on preferences of mothers for HPV vaccines for their daughters.

Our study addresses three research questions. First, we hypothesized that consumers would have clear preferences over several features of HPV vaccines, favoring cervical cancer protection over all other features. To test and quantify this, we developed a CA survey and estimated the relative importance of difference vaccine features. Given related findings in the literature [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], we also assumed that these preferences would differ by some individual characteristics and assessed this through extensions of the main preference model. Second, we postulate that the estimated value of consumer benefits would exceed the current retail prices of HPV vaccines given the positive and increasing demand for HPV vaccines [20]. This was tested by using the CA results to estimate the average maximum “willingness-to-pay” (WTP) among our survey sample. WTP is the value that individuals place on the vaccine and may be used as a measure of private economic benefits in cost-benefit analyses of vaccine programs. Finally, we hypothesized that total uptake of HPV vaccines would increase when a second vaccine was added to the U.S., although only one was available at the time of our survey. We tested this by using the main survey data and model to predict uptake under a variety of different scenarios.