Since it became available in the United States in 2006, the Human Papillomavirus (HPV) vaccine has been a source of debate, with proponents lauding it as a substantial gain in the fight against cancer, and opponents concerned with its implications for sexual activity among youth. With the U.S. Food and Drug Administration’s recent approval of Gardasil-9 — a vaccine that protects against nine of the most common strains of HPV that account for approximately 90 percent of cervical, vulvar, vaginal and anal cancers — there is both a renewed interest and concern that calls for a nuanced and comprehensive review of the science.
HPV is the most common sexually transmitted infection in the United States, with nearly all sexually active men and women believed to contract at least one form of it during their lifetime. According to the U.S. Centers for Disease Control and Prevention (CDC), an estimated 79 million Americans have HPV, and about 14 million become newly infected annually. While most infections clear the body within two years, some can persist and result in genital warts, cervical cancer or other types of cancers in men and women. Of the many HPV strains that exist, HPV types 16 and 18 have been identified as high risk, accounting for about 70 percent of all cervical cancer, as well as a large proportion of other HPV-related cancers.
While cervical cancer was previously a leading cause of death among women in the U.S., death rates declined substantially after the introduction of the Pap test in the 1950s. Nevertheless, according to the CDC, more than 12,000 women in the U.S. are diagnosed with cervical cancer each year, and more than 4,000 die from it. Public discourse around HPV tends to focus on the health of women because they disproportionately bear the burden of its health consequences. However, men also face substantial risk, particularly as it relates to oral and anal cancers.
Although screening procedures are in place for early detection of cervical cancer, there are no comparable strategies to identify HPV-related cancer in its early stages for men. Consequently, the administration of a vaccine to prevent infection and transmission presents an important line of protection. Currently, the HPV vaccine is administered over a course of three injections, which must be completed within six months to confer full protection. A 2012 review of clinical trials of HPV vaccines shows that vaccines designed to protect against two or four of the most common strains have very high efficacy rates, ranging between 90 percent and 100 percent. For that reason, large public health efforts have focused on improving vaccination rates before boys and girls become sexually active.
Today, both the CDC and American Academy of Pediatrics recommend routine vaccination against HPV for all 11-year-olds and 12-year-olds in the U.S. Although the early age of vaccination has been a source of public debate, medical recommendations are based partly on evidence that shows that antibody responses are highest during this age period. Also, it is a good idea to vaccinate adolescents before they come into contact with the virus as the vaccine is not effective against HPV types that already have been acquired. Despite such recommendations from medical professionals, vaccination completion rates remain low — 40 percent for girls and 20 percent for boys in 2014. That is substantially lower than the vaccination rate for tetanus, diphtheria, and pertussis and the vaccination rate for meningitis among members of the same age group.
Below are a series of studies that will help journalists understand and explain this important health topic from a variety of angles, including vaccine safety and racial and gender disparities in vaccination rates. Beat reporters can find related reports and statistics from organizations such as the CDC, National Cancer Institute and World Health Organization.
Barriers to vaccination
“Reasons for Not Vaccinating Adolescents: National Immunization Survey of Teens, 2008-2010”
Darden, P.M.; et al. Pediatrics, April 2013, Vol. 131. doi: 10.1542/peds.2012-2384.
Summary: Using data from the National Immunization Survey of Teens, researchers found that parental intentions to not vaccinate for HPV increased from 39.8 percent in 2008 to 43.9 percent in 2010. The most commonly cited reasons for not vaccinating were “not recommended/needed,” “not sexually active,” and “safety concerns/side effects.” Vaccine safety concerns increased from 4.5 percent in 2008 to 16.4 percent in 2010.
“Barriers to Human Papillomavirus Vaccination Among US Adolescents: A Systematic Review of the Literature”
Holman, D.M.; et al. JAMA Pediatrics, January 2014, Vol. 168. doi: 10.1001/jamapediatrics.2013.2752.
Summary: “Health care professionals cited financial concerns and parental attitudes and concerns as barriers to providing the HPV vaccine to patients. Parents often reported needing more information before vaccinating their children. Concerns about the vaccine’s effect on sexual behavior, low perceived risk of HPV infection, social influences, irregular preventive care, and vaccine cost were also identified as potential barriers among parents.”
“Adverse Events Following Immunization in Ontario’s Female School-Based HPV Program”
Harris, T.; Williams, D.M.; Feiurek, J.; Scott, T.; Deeks, S.L. Vaccine, January 2014, Vol. 32. doi: 10.1016/j.vaccine.2014.01.004.
Summary: After a school-based HPV vaccination program was implemented among eighth grade girls in Ontario, Canada, researchers analyzed reports of adverse events following immunization over the following four years. From 2007 to 2011, nearly 700,000 HPV vaccine doses were administered and 133 confirmed cases of adverse events were reported. The most commonly reported side effects included allergic reactions (25 percent), rashes (22 percent), reactions at the injection site (20 percent), and non-specific “other events” (26 percent). Ten serious cases were identified, which included two cases of anaphylaxis, two seizures, one thrombocytopenia, and one death, which was concluded by the coroner to be due to a previously undiagnosed cardiac condition. Ultimately, the researchers conclude that the findings are in line with existing evidence on the safety profile of the HPV vaccine, and no new safety concerns were identified.
“Safety of Human Papillomavirus Vaccines: A Review”
Macartney, K.K.; Chiu, C.; Georgousakis, M.; Brotherton, J.M.L. Drug Safety, June 2013, Vol. 36. doi: 10.1007/s40264-013-0039-5.
Abstract: “Both vaccines are associated with relatively high rates of injection site reactions, particularly pain, but this is usually of short duration and resolves spontaneously. Systemic reactions have generally been mild and self-limited. Post vaccination syncope has occurred, but can be avoided with appropriate care. Serious vaccine-attributable adverse events, such as anaphylaxis, are rare, and although not recommended for use in pregnancy, abnormal pregnancy outcomes following inadvertent administration do not appear to be associated with vaccination. HPV vaccines are used in a three-dose schedule predominantly in adolescent females: as such, case reports linking vaccination with a range of new onset chronic conditions, including autoimmune diseases, have been made. However, well-conducted population-based studies show no association between HPV vaccine and a range of such conditions.”
Questions about effective dosage
“Immunogenicity of the 9-Valent HPV Vaccine Using 2-Dose Regimens in Girls and Boys vs a 3-Dose Regimen in Women”
Iversen, Ole-Erik; Miranda, Maria Jose; Ulied, Angels. JAMA, 2016. doi:10.1001/jama.2016.17615.
Conclusions and Relevance: “Among girls and boys aged 9 to 14 years receiving 2-dose regimens of a 9-valent HPV vaccine separated by 6 or 12 months, immunogenicity four weeks after the last dose was non-inferior to a 3-dose regimen in a cohort of adolescent girls and young women. Further research is needed to assess persistence of antibody responses and effects on clinical outcomes.”
“Immunogenicity and HPV Infection after One, Two, and Three Doses of Quadrivalent HPV Vaccine in Girls in India: a Multicentre Prospective Cohort Study”
Sankaranarayanan, Rengaswamy; et al. The Lancet, January 2016, Vol. 17. doi: http://dx.doi.org/10.1016/S1470-2045(15)00414-3.
Interpretation: “Despite the limitations imposed by the suspension of the HPV vaccination, our findings lend support to the WHO recommendation of two doses, at least 6 months apart, for routine vaccination of young girls. The short-term protection afforded by one dose of HPV vaccine against persistent infection with HPV 16, 18, 6, and 11 is similar to that afforded by two or three doses of vaccine and merits further assessment.”
Disparities in vaccination rates
“Racial/Ethnic and Poverty Disparities in Human Papillomavirus Vaccination Completion”
Niccolai, L.M.; Mehta, N.R.; Hadler, J.L. American Journal of Preventive Medicine, 2011, Vol. 41. doi: 10.1016/j.amepre.2011.06.032.
Abstract: “Data from the 2008-2009 National Immunization Survey-Teen for girls aged 13-17 years who received at least one dose of HPV vaccine (n=7606) were analyzed in 2010-2011. During this 2-year period, 55 percent of adolescent girls who initiated vaccination completed the three-dose series. Completion was significantly higher in 2009 (60 percent) compared to 2008 (48 percent; p<0.001). After controlling for covariates, adolescents who were black or Hispanic were significantly less likely to complete vaccination than whites. Adolescents living below the federal poverty level were significantly less likely to complete vaccination than adolescents with household incomes >$75,000.”
“Social Inequalities in Adolescent Human Papillomavirus (HPV) Vaccination: A Test of Fundamental Cause Theory”
Polonijo, A.N.; Carpiano, R.M. Social Science & Medicine, 2013, Vol. 82. doi: 10.1016/j.socscimed.2012.12.020.
Abstract: “Analyses of 2008, 2009, and 2010 United States National Immunization Survey-Teen data (n = 41,358) reveal disparities particularly for vaccine knowledge and receipt of a health professional recommendation. While parental knowledge is a prerequisite to adolescent vaccine uptake, low socioeconomic status (SES) and racial/ethnic minority parents have significantly lower odds of knowing about the vaccine. Receipt of a health professional’s recommendation to vaccinate is strongly associated with vaccine uptake, however the odds of receiving a recommendation are negatively associated with low SES and black racial/ethnic status.”
“Sociodemographic Differences in Human Papillomavirus Vaccine Initiation by Adolescent Males”
Agawu, A.; et al. Journal of Adolescent Health, November 2015, Vol. 57. doi: 10.1016/j.jadohealth.2015.07.002.
Summary: Researchers studied patterns of HPV vaccination among a sample of 58,757 adolescent males between the ages of 11 and 18 in a large primary care network. Results showed that African American males with private health insurance were twice as likely to initiate vaccination than White males with private insurance, while African American males on Medicaid were nearly three times more likely. Similar trends were observed among Hispanic males. The authors conclude that, “although the true mechanism underlying these differences remains unknown, potential candidates include provider recommendation patterns and differential vaccine acceptance within these groups.”
HPV vaccine and young males
“HPV Vaccination Coverage of Male Adolescents in the United States”
Lu, P.J.; et al. Pediatrics, October 2015, Vol. 136. doi: 10.1542/peds.2015-1631.
Summary: Researchers used data from the 2013 National Immunization Survey-Teen to investigate trends in HPV vaccination of adolescent boys. Findings revealed low rates of both vaccine uptake (34.6 percent) and completion (13.9 percent), however African American and Hispanic males were more likely to receive the vaccine than their White peers. In order to improve vaccination coverage, the authors conclude that a comprehensive approach is needed which includes physicians regularly assessing their patient’s vaccination status, educating doctors about current HPV vaccine recommendations as well as information on vaccine efficacy and safety, reducing costs, and improving health communication strategies to dispel misinformation about the vaccine.
“Longitudinal Predictors of Human Papillomavirus Vaccination Among a National Sample of Adolescent Males”
Reiter, P.L.; et al. American Journal of Public Health, August 2013, Vol. 103. doi: 10.2105/AJPH.2012.301189.
Abstract: “In fall 2010 and 2011, a national sample of parents with sons aged 11 to 17 years (n = 327) and their sons (n = 228) completed online surveys to identify predictors of HPV vaccination. Only 2 percent of sons had received any doses of HPV vaccine at baseline, with an increase to 8 percent by follow-up. About 55 percent of parents who had ever received a doctor’s recommendation to get their sons HPV vaccine did vaccinate between baseline and follow-up, compared with only 1 percent of parents without a recommendation. Willingness to get sons the HPV vaccine decreased from baseline to follow-up among both parents and sons.”
“Acceptability of Human Papillomavirus Vaccine for Males: A Review of the Literature”
Liddon, N.; Hood, J.; Wynn, B.A.; Markowitz, L.E. Journal of Adolescent Health, 2010, Vol. 46. doi:10.1016/j.jadohealth.2009.11.199.
Abstract: “Among mothers of sons, support of HPV vaccination varied widely from 12 percent to 100 percent, depending on the mother’s ethnicity and type of vaccine, but was generally high for a vaccine that would protect against both genital warts and cervical cancer. Health providers’ intention to recommend HPV vaccine to male patients varied by patient age but was high (82 percent-92 percent) for older adolescent patients. A preference to vaccinate females over males was reported in a majority of studies among parents and health care providers. Messages about cervical cancer prevention for female partners did not resonate among adult males or parents. Future acceptability studies might incorporate more recent data on HPV-related disease, HPV vaccines, and cost-effectiveness data to provide more current information on vaccine acceptability.”
“Parents’ Decisions About HPV Vaccine for Sons: The Importance of Protecting Sons’ Future Female Partners”
Schuler, C.L.; DeSousa, N.S.; Coyne-Beasley, T. Journal of Community Health, October 2014, Vol. 39. doi: 10.1007/s10900-014-9859-1.
Abstract: “76 percent of parents reported vaccine decisions for sons were likely to be influenced by preventing HPV transmission from sons to their female partners. Parents likely to be influenced by female partner protection in vaccine decisions had greater intention to vaccinate sons than their counterparts (adjusted odds ratio 2.54). Because parents likely to consider female partners had increased intention to vaccinate sons, future efforts to improve vaccine uptake in boys should explore the benefits of highlighting potential female partner protection, as this concept may resonate with many parents.”
“Epidemiologic Impact of HPV Vaccination and Evidence for Herd Immunity Over the First 8 Years after Vaccine Introduction in a Community”
Widdice, Lea E.; et al. Journal of Adolescent Health, February 2016, Vol. 58. doi: http://dx.doi.org/10.1016/j.jadohealth.2015.10.033.
Conclusions: “Over the first eight years after HPV vaccine introduction, vaccine-type HPV decreased by about 75 percent among all women, demonstrating high effectiveness in a community setting even in sexually experienced young women who may have already been exposed to HPV. We also found substantial evidence for herd immunity.”
Keywords: adolescent, vaccination, immunization, preventive health, teenager, HPV, genital warts, cervical cancer, sexual partner