Factors influencing the uptake of the human papillomavirus (HPV) vaccine to prevent cervical cancer (CC)
The Abramson Cancer Center of the University of Pennsylvania
Last Modified: June 7, 2010
Presenter: J. Y. Lai, PhD; Division of Medical Oncology, British Columbia Cancer Agency, Vancouver, BC, Canada
- Cervical cancer is a major cause of cancer morbidity and mortality worldwide, with an estimated 11,270 new cases in the United States in 2009.
- Gardasil is a vaccine that has been developed to immunize patients against the most common oncogenic HPV types (16 and 18, responsible for 70% of cervical cancer).
- The vaccine was approved by the FDA in 2006, and the CDC recommends vaccination of women and girls age 9 — 26, with 3 sequential injections.
- Vaccination of men and boys in the same age group was recently approved. Approval of use of Gardasil in older women and men is currently pending.
- Despite Gardisil's ability to prevent cervical cancer, rates of HPV vaccination are relatively low.
- A CDC study reported in March 2010 that although 25% of adolescents 13 to 17 years old reported receiving at least 1 dose of the vaccine, only 11% reported receiving all 3 doses. (2010 National STD Prevention Conference (NSTDP): Abstract LBb. Presented March 10, 2010)
- The reasons for poor uptake of the HPV vaccine are largely unknown but may be due to several factors, including:
- Suboptimal public acceptance of the vaccine (skepticism),
- Lack of knowledge related to cervical cancer, and the causative role of HPV.
- Limited access to health care services among patients of lower socioeconomic background.
- Prohibitive cost of vaccination.
- It has been shown that the mother's approval of HPV vaccination is an important factor associated with vaccination status (Roberts, Pediatrics, 2010).
- 3 common barriers to vaccination reported by parents (in the CDC study) were the belief that the child did not need the vaccine, a lack of sufficient vaccine knowledge, and the fact that the child was not sexually active.
- The authors hypothesized that lack of knowledge was the primary factor driving the lack of acceptance of HPV vaccination, and set out to test this hypothesis by:
- 1) evaluating the willingness of U.S. women to use the HPV vaccine,
- 2) examining their current understanding of HPV infection and its association with cervical cancer, and
- 3) determining the impact of knowledge level and sociodemographic factors on attitudes toward using the HPV vaccine.
- The study authors identified women aged ? 18 years from the U.S. population-based Health Information National Trends Survey (HINTS 2007), which is designed to represent the US population.
- They asked the question: "Would you vaccinate your daughter against HPV?," and also asked 6 general questions related to HPV, its role in cervical cancer, and the vaccine.
- Based on the number of correct responses, individuals were given a score from 0 to 6 to quantify their understanding about HPV and its role in cervical cancer (score of 0 = poor and 6 = excellent awareness).
- Logistic regression and interaction analyses were conducted to explore the influence of this knowledge level, and other clinical factors, on the decision to apply the HPV vaccine.
- There were 804 female respondents and all were included in the analysis.
- Mean age was 44.9 (SD = 2.53) years
- 73% were white.
- 67% had a routine Pap smear within the past year
- 75% of women indicated they would immunize their daughters against HPV.
- Mean knowledge score was excellent (5.6) (SD = 0.30), but
- Understanding about (a) the route of HPV transmission and (b) the causal relationship between HPV infection and cervical cancer was the most limited of all areas..
- On univariate analysis, individuals who were white, educated, and high income earners, as well as those with a family history of any cancer were more knowledgeable about HPV than there counterparts (all p < 0.05).
- On multivariate analysis, only never smokers were significantly more likely to have increased knowledge about HPV.
- In multivariate models of factors associated with likelihood of vaccination,
- White race correlated with a higher likelihood of using the HPV vaccine (OR = 1.86, p = 0.04), but
- Knowledge level did not (OR = 0.47, p = 0.22).
- In this population-based sample of U.S. women, knowledge level was generally high, but it was not associated with the use of the HPV vaccine.
- Acceptance of the vaccine among survey respondents was high (75%).
- Race was a significant factor in the likelihood of respondents to use the HPV vaccine.
- Factors that are commonly associated with racial differences in cancer care, such as inferior access to the healthcare system and prohibitive treatment-related costs, may be significant barriers to vaccine use.
- Interventions focused on alleviating these racial disparities might better modify the uptake of the HPV vaccine
- The study authors hypothesized that lack of knowledge among women about HPV, its association with cervical cancer, and the HPV vaccine is driving the low rates of HPV vaccination.
- Therefore, they set about to quantify knowledge of HPV among a representative sample of the US population, and determine if their level of knowledge correlates with respondents' willingness to use the vaccine.
- Their survey captured women with a mean age of 45; this represents an important group of women in that mothers' perception of the HPV vaccine has been shown to be an important factor in young women's willingness to be vaccinated.
- They found that the level of knowledge was actually quite high (5.6 on a scale of 0-6), but that knowledge did not correlate with willingness to use the vaccine, and as such it was a negative study.
- A potential flaw of the study is that it used an unvalidated model to assess HPV knowledge, which raises at least 2 concerns:
- Was the knowledge tested relevant to the considerations of mothers whether to vaccinate their daughters?
- Did their metric lack sensitivity to detect significant differences in knowledge among respondents?
- The positive finding of the study is that, on multivariate analysis, race is the only significant factor in the likelihood of respondents to use the HPV vaccine.
- The reasons for this are not clear. The authors hypothesize that this may be due to factors such as inferior access to the healthcare system and prohibitive treatment-related costs.
- However, one would not expect these factors to effect mothers' willingness to vaccinate their daughters, but rather their ability to translate willingness into action.
- The study did not assess belief systems or other factors that would explain the potential impact of race on willingness to vaccinate, and as such this remains an open question that should be evaluated in future studies.