During 2008 through 2018, we administered a series of four surveys about HPV vaccination to national networks of physicians who spent at least half of their time practicing primary care. The surveys were conducted in January-March 2008, July-September 2010, (October 2013–January 2014, and July-September 2018. The human subjects review board of the University of Colorado Denver approved these studies as exempt research not requiring written informed consent.

Response rates among physicians were 80% in 2008 (680/848), 72% in 2010 (609/842), 70% in 2014 (582/829), and 65% in 2018 (588/908). Respondent and non-respondent characteristics are presented in Table 1 online.

This analysis showed the proportion of U.S. primary care physicians who strongly recommend HPV vaccination for both male and female adolescents has increased over the past decade, as scientific evidence has continued to accumulate for safety and effectiveness of HPV vaccination. At the same time, physicians perceived few barriers in general to HPV vaccination, although more reported awareness of certain parental concerns. Physician concerns about vaccine efficacy, need for vaccination, and vaccine safety were rarely barriers to HPV vaccination and remained stable or decreased over time. Physicians perceived that parental questions about need for vaccination and concerns about vaccine safety and moral and religious issues remained barriers to HPV vaccination; many of these perceived concerns increased over time.

Examining this series of surveys over time reveals encouraging improvements in physician recommendations for HPV vaccination as well as some targets for building upon this progress. Since HPV vaccine was first introduced for routine use, the proportion of physicians strongly recommending the vaccine has increased from just over 50% to 77% for 11–12-year-old female patients and to 73% for 11–12-year-old male patients. Receiving a strong recommendation from a provider is associated with HPV vaccine acceptance, and lack of a strong recommendation from a provider is a barrier to HPV vaccination.^{8, 17, 18} Family physicians were less likely to strongly recommend HPV vaccination than pediatricians in 2014 (male patients) and 2018 (female and male patients). Work to improve physician recommendations should focus on family physicians as they provide care for a large proportion of US adolescents¹⁹ and remain less likely than pediatricians to strongly recommend HPV vaccination.

Our surveys confirmed physicians remain less likely to strongly recommend HPV vaccination to male patients than to female patients, although this disparity has decreased over time.²⁰ One study examining gender disparities in HPV vaccination found parents of unvaccinated adolescent sons were more likely to report not receiving a provider recommendation compared to parents of unvaccinated adolescent daughters.²¹ Additional work has found parental HPV vaccine acceptance for adolescent males is associated with perceived provider knowledge²², perceived future benefits of vaccination for the adolescent and his future partners, and perceived future regrets related to not vaccinating.²³ Nevertheless, data from the National Immunization Survey- Teen in 2019 show 70% of 13–17-year-old males and 73% of females of the same age had received ≥1 dose of HPV vaccine, continuing a trend of increased HPV vaccination among male adolescents and a narrowing gap between males and females. While physicians increasingly strongly recommend HPV vaccination, communication should include messages about the benefits of HPV vaccination for adolescents regardless of sex.

Physician beliefs were rarely barriers to HPV vaccination and remained stable or decreased over time. Of note, financial and practice barriers related to HPV vaccination, which were more common than any physician concerns related to HPV vaccine efficacy, need for vaccination, or vaccine safety decreased from 2008 to 2018. These findings suggest physician education about and experience with HPV vaccine have been successful in reducing physician barriers to HPV vaccination.

Perceived parental barriers related to need for vaccination, vaccine safety, sexual behavior and moral/religious concerns were common and several of these barriers were reported by more physicians over time. By 2018, a majority of physicians reported parents not thinking HPV vaccination is necessary was a major barrier/somewhat of a barrier- 67% and 59% for male and female adolescents respectively. Analysis of parent responses to the National Immunization Survey (NIS)-Teen data found that about one-third of parents of unvaccinated teens reported that the HPV vaccine was not necessary in 2015.²⁴ Viewed within the Health Belief Model, this barrier about need for vaccination may reflect parental perceptions of their adolescent’s susceptibility to HPV, the severity of HPV, and/or the benefits of HPV vaccination.²⁵ Many prior studies have shown parental perception of HPV risk and the benefits of vaccination influence vaccination decisions for their sons and daughters.^{8, 26, 27} A belief of not being at risk for HPV was also a reason for forgoing vaccination among adolescent women 15–24 years of age.²⁸ Lack of awareness about HPV and associated cancers has been identified as a barrier since HPV vaccine was first introduced; our survey results suggest that this remains a parental barrier to vaccination. Communication and education efforts to reach parents directly and to improve physician communication must continue to emphasize the high prevalence of HPV infection, the risks associated with HPV infection and HPV-related cancers, and the cancer prevention benefits of HPV vaccination.^{29, 30}

Parental safety concerns were reported as a major barrier/somewhat of a barrier by 29% of physicians in 2008 and 73% in 2018, with concerns about long-term complications from vaccination and giving too many vaccines at once recognized as prominent safety concerns. Questions about vaccine safety are a challenge for vaccine acceptance in general and have been identified in prior HPV work.⁸ In NIS-Teen parent surveys concerns about HPV vaccines safety decreased among parents of unvaccinated females but increased among parents of unvaccinated males between 2010 and 2015.²⁴ Recent studies have examined the influence of misinformation from social media on vaccine safety concerns^{31, 32} and a few studies have used social media to promote HPV vaccination.^{33, 34} Parental concern about HPV vaccine causing infertility was uncommon but increased from 2014 to 2018 even as studies have shown HPV vaccination is not associated with female infertility.^{35, 36} Identifying these sorts of infrequent yet growing safety concerns is key to development of targeted public health messages for dissemination by health care providers and through social media.

Moral/religious concerns and concerns about the influence of HPV vaccination on adolescent sexual behavior represent a category of parental barriers that physicians perceive to be increasingly common. Parental concerns about earlier or more risky sexual behavior were perceived to be more common for adolescent females than males and increased for females between 2008 and 2018. Several other studies have identified moral/religious concerns and questions about sexual behavior as parental barriers to HPV vaccination across diverse geographic, racial and ethnic populations since introduction of the vaccine.^37–39 Physician perception is that these parental concerns have increased with time, suggesting a continued association of HPV vaccination with sex rather than cancer prevention. Myths about HPV vaccination encouraging earlier or riskier sexual behavior have been disproven.^{40, 41} Moral/religious vaccine concerns may be addressed by reframing HPV vaccination as cancer prevention, and may also benefit from more in-depth exploration of the role of social and community norms and the role of values in adolescent vaccination.

The data from these nationally representative surveys should be interpreted in the context of some limitations. Responses from sentinel physicians surveyed may not be completely generalizable, although prior work showed that the survey methods described here yield demographic and vaccine attitude responses similar to responses of physicians sampled randomly from AMA physician databases.¹³. Survey non-respondents may have different views and experiences than respondents. Depending on how vaccine attitudes and experiences of non-respondents differed from respondents in each survey year, year to year comparisons may not be representative of true differences among all physicians. Survey data are based on self-report rather than direct observation and may not reflect actual physician practice. Analysis of temporal trends in barriers to HPV vaccination included multiple comparisons; therefore, statistical significance of changes in barriers over time should be interpreted with caution. Individual barrier items were measured at different points in time but not all barriers were measured in all survey years. Barriers represent physician perceptions of parent beliefs but actual parent beliefs or the proportion of parents with any given belief were not measured. Noting that reported parental refusal of HPV vaccination remained stable (females) or decreased (males), caution should be used in interpreting physicians’ report of increasing parental barriers. Parents who refuse vaccination in more recent survey years may have strongly held beliefs and may articulate their reasons for refusing vaccination more clearly to physicians, or unmeasured factors may have made physicians more attuned to perceived parental barriers over time.

Through a series of surveys between 2008 and 2018, we demonstrated that strength of physician recommendations for HPV vaccination has increased, reported parental refusals of HPV vaccine have decreased somewhat, and physician barriers to vaccination have decreased. However, perceived parental barriers have increased with concerns about the need for vaccination, vaccine safety, and moral/religious issues persisting as common barriers. To maintain and improve HPV vaccine confidence, communication and educational strategies should present HPV vaccination as cancer prevention to move the focus away from sexuality²⁹, emphasize the need for vaccination by focusing on the risks of HPV infection³⁰, and counteract misinformation about vaccine safety including through social media interventions. Efforts to address parental barriers should be paired with communication strategies proven effective at increasing HPV vaccine uptake such as motivational interviewing and a strong provider recommendation.^{17, 18, 42, 43}