Human Papillomavirus Vaccination Rates of Military and Civilian Male Respondents to the Behavioral Risk Factors Surveillance System Between 2013 and 2015 Free

Abstract

Objective

To evaluate human papillomavirus (HPV) vaccination rates among men in the USA and to compare vaccination rates among men who had served in the military to those reporting no previous military service.

Methods

We performed a cross-sectional analysis using Behavioral Risk Factor Surveillance System (BRFSS) data from the 2013 to 2015 to analyze HPV vaccination rates for vaccine eligible adult men. The BRFSS is a multistage, cross-sectional telephone survey conducted nationally by state health departments. Univariable and logistic regression analyses were performed to examine the relationship between military service and HPV vaccination status was assessed as well as the number of HPV vaccination doses received.

Results

A total of 5,274 participants were analyzed representing a weighted estimate of 1.5 million HPV vaccine eligible men in the USA. The vaccination rate among veterans was 25.3% (95% confidence interval (CI), 18.8–33.3%) compared to 15.9% (95% CI, 14.3–17.6%) for civilians (p < 0.01). Veterans were more likely to report having received at least one dose of the HPV vaccine compared to civilian men (adjusted odds ratios [aOR] = 2.7, 95% CI, 1.7%-4.1%, p < 0.001).

Conclusions

Veteran men are more likely to have received HPV vaccination than similarly aged civilian men. However, for both civilians and veterans, the HPV vaccination coverage remains low when compared to their female counterparts.

INTRODUCTION

Human papilloma virus (HPV) is the most common sexually transmitted infection (STI) in the USA.¹ Men are often unknowingly infected; reports show positive testing in up to 72.9% of men depending on the specific population and site tested.² Han et al study showed genital HPV infection rates of 45.2% in adult men.³ Infection with an oncogenic strain of HPV is responsible for 91% of anal and 63% penile cancers in men.⁴ While cancers of the head and neck are traditionally thought to be primarily caused by tobacco and alcohol use, recent studies show that about 70% of cancers of the oropharynx may be linked to HPV infection.^4–6 From 2009 to 2013, the Centers for Disease Control and Prevention (CDC) reported approximately 39,800 HPV-associated cancers annually in the United States, affecting over 16,500 men.⁴

Fortunately, there are currently three approved vaccines which can prevent HPV infection in both men and women. Traditionally, the HPV vaccination completion required three injections. In 2016, Advisory Committee on Immunization Practices approved a two-dose series for vaccination in individuals who initiate the series between ages 9 and 14. Despite the established efficacy and safety of the HPV vaccine, vaccination rates in men remain historically low with one report showing only 10.7% of men have received at least one dose of the vaccine.³ Poor HPV vaccination rates are particularly concerning for the military population, as members of the military historically have been shown to have a greater incidence of sexually transmitted infections and higher numbers of sexual encounters compared to their civilian counterparts.^7,8 Not only is this concerning for these individuals, but also for their sexual partners.

The purpose of this study was to evaluate if men with military service were more likely to receive the HPV vaccine compared to an equivalent civilian cohort. This is of particular interest given the military population’s increased rates of sexually transmitted infections and improved access to healthcare, as the vaccination is covered under Tricare and presents no financial cost to beneficiaries.

METHODS

The Behavioral Risk Factor Surveillance System (BRFSS) is the world’s largest continuous health survey, with more than 400,000 interviews yearly.⁹ Landline and cellular telephone surveys are conducted annually by the CDC across all 50 states, the District of Columbia, and selected U.S. territories using a standardized instrument. The survey is designed to measure behavioral risk factors for the adult population and is administered to a stratified random sample of the U.S. population aged 18 and older. Nationally representative estimates are accomplished using iterative proportional fitting to weight samples. Nonresponse bias and error within estimates are minimized through sample weighting.

We conducted a retrospective review using data from three consecutive survey years, 2013–2015. Variables of interest included gender, age, race/ethnicity, marital status, level of education, income, access to health care, veteran status, and HPV vaccination status. Vaccine eligibility differed for each survey year and was based on a participant being no more than 26 years old in 2011. Thus, men aged 18 to 28 were included from the 2013 BRFSS survey. In the 2014 and 2015 survey years age cut point was increased to 29 and 30 years, respectively. The vaccination rate was defined as those reporting at least one dose of HPV vaccination, while series completion was defined as those who reported receiving three doses, which was the recommended regimen at the time of survey completion.

Summary statistics are provided for categorical variables and include the number of participants as well as the weighted prevalence within each category. Prevalence and prevalence ratios were estimated from weighted frequencies. To account for unequal selection probabilities among participants and adjustments for non-response, weighted estimates are provided using 3-year sampling weights. Rao-Scott adjusted Chi-square tests of independence were used for domain analyses.

Participants’ age and marital status were used as covariates in the regression model to assess the independent relationship between military service and HPV vaccination. Several variables were examined as potential predictors; these variables included age, race/ethnicity, marital status, education level, and income level. To reach the final reduced model, we used backward elimination with a threshold of p < 0.05 for retention. Excluded variables were then added back into the final model individually so that changes in the β coefficients of the statistically significant main effect could be assessed. If addition of one of these excluded variables caused a change in a β coefficient by ≥10%, the variable was re-added to the model. Odds ratios (ORs) and adjusted odds ratios (aORs) with 95% Wald confidence intervals (CIs) were estimated using logistic regression models. Variance estimates in weighted logistic regressions were made with the Taylor series linearization approach.

Statistical significance was based on a significance level of p < 0.05 threshold for all statistical tests. All analyses were conducted using the complex sample package for SPSS Complex Samples version 23 (IBM, Armonk, NY, USA). An Institutional Review Board waiver was obtained in accordance with the use of publicly available de-identified data.

RESULTS

Mean survey response rates from 2013 to 2015 ranged between 37.8% and 48.2%. The cohort of vaccine eligible men who were questioned about their HPV vaccination history included 5,274 men. Among this cohort 6.7% (95% CI, 5.7–7.8%; N = 331) endorsed a history of military service and 93.3% (95% CI, 92.2–94.3%; N = 4,943) reported no military service. Demographic characteristics including age, race/ethnicity, marital status, education level, and income were all analyzed for both veteran and civilian participants (Table 1).

No differences were observed between the veteran and civilian respondents based on race/ethnicity. The civilian group was younger overall compared to the veterans, p < 0.001. While there was no difference in the proportion of individuals describing themselves as divorced, widowed, or separated; veterans were twice as likely (OR, 2.2; 95% CI, 1.5–3.1) to report being married or a member of an unmarried couple (38.0%; 95% CI, 30.6%–46.1%) than their civilian counterparts (22.9%; 95% CI, 21.2%–24.6%). There were significant differences in level of education and income between veterans and civilians, with veterans less likely to have a college degree but more likely to have graduated high school (Table 1).

Total HPV vaccination coverage among eligible adult men between 2013 and 2015 was 16.5% (95% CI 15.0%–18.2%). There was no difference in vaccination rates between survey years, (p = 0.45). Among veterans the overall vaccination rate was 25.3% (95% CI 18.8 %–33.3%) compared to 15.9% (95%CI, 14.3%-17.6%) among the civilians (p < 0.01). No difference was found between the two groups in reported access to healthcare (Table 2).

Multivariable logistic regression analysis indicates that when differences in age and marital status are controlled for, veterans were more than twice as likely to report having received at least one dose of the HPV vaccine compared to civilian men (aOR = 2.7; 95% CI, 1.7–4.1; p < 0.001). Subgroup analysis showed the most significant difference in vaccination rate between the veteran and civilian participants in the 22 to 24 year-old age category, with a more than six-times-likelihood to report at least one dose of the HPV vaccine (OR = 6.5, 95% CI, 3.3–13.1) (Table II). Among veterans, 57.5% (95% CI, 40.3%–73.1%) reported only receiving a single dose of vaccine while 27.8% (95% CI, 14.6%–46.6%) reported vaccine series completion. In contrast, 33.0% (95% CI, 28.0%–38.4%) of civilians reported only receiving a single dose of vaccine and 41.5% (95% CI, 35.7%–47.5%) reported vaccine series completion.

DISCUSSION

The purpose of this study was to evaluate if men with military service were more likely to receive HPV vaccination when comparted to their equivalent civilian cohorts. The rate of vaccination among veteran men was 25.3% (95% CI, 18.8%–33.3%) compared to 15.9% (95% CI, 14.3%–17.6%) in civilian men (p < 0.01) despite the younger demographic distribution in civilian group, which was closer to the HPV vaccination recommended age. Higher vaccination rate in the veteran group may reflect better access to health care compared to civilian counterpart with 100% health care cost coverage and no penalty for receiving medical care.

Compared to the 2006–2009 Navy retrospective cross-sectional study that showed vaccination rates of only 3% for men, this study shows a significant improvement in vaccination rates.¹⁰ It should be noted that this study was performed near the time that the HPV vaccine was approved for men and included data primarily for a military population with a small amount of civilians included. This study is consistent when compared to the 2010 National Health Interview survey showing HPV vaccination rate among men aged 18–26 years was only 1.1%.¹¹ This may be due in part to the fact that the HPV vaccine was not FDA approved for men until 2009 and not recommended for men until 2011 in the USA. Despite improved vaccination rates compared to previous studies, this analysis still shows significant room for improvement and the continued trend of poor vaccination rates and disparities from female counterparts. Female vaccination rates in the military have been reported at 63.8% compared to civilian vaccination rates of 41.8%, suggesting that military vaccination rates have been improving in recent years.¹²

Human papillomavirus is the only vaccine approved for cancer prevention; improvements in vaccination rates could result in a drastic decrease in HPV related cancers in both men and women. Considering the higher rates of sexually transmitted infections, the military male population is a possible area of focus for future efforts to improve male HPV vaccination rates. There is a high prevalence of HPV infection in males, who are asymptomatic when infected and act as a reservoir for female HPV infection, which can lead to cervical, vulvar, and vaginal dysplasia/cancer. The literature continues to support the safety and effectiveness of the HPV vaccination, with vaccinated individuals still showing evidence of immunity up to 12 years later.¹³ In areas where vaccination rates are high, benefits of herd immunity could potentially be obtained. The current association of HPV vaccination and herd immunity are currently undetermined. Tarney et al. presented that there have been no changes in unvaccinated women in the USA comparing a pre-vaccination era to post vaccination era. However, a Scotland based study showed decreased rates in nonvaccinated women after implementation of a national immunization program.^14,15 Military members are a highly mobile population and thus may not reap the full benefits of regional herd immunity; furthermore, the mobile nature of this population makes vaccination even more important to prevent HPV transmission.

Despite the extensive access to care without co-pays military members and their families have, there are still low rates of HPV vaccination. A benefit of targeting HPV vaccination efforts to the military population is that access to healthcare and vaccine cost should not be a significant barrier to patients. Interventions such as incorporating HPV vaccination as an opt out vaccine into military in-processing healthcare could lead to a vast increase in the number of males vaccinated, as well as increase female vaccination rates. The military does not currently require HPV vaccination for servicemembers. Studies focused on influenza vaccination have shown a significant increase in vaccination rates when implemented as an opt out program compared to an opt in system.¹⁶ This is an excellent way to increase vaccination rates while still allowing for patient autonomy. Future studies should work towards identifying obstacles that contribute to low adherence in the military population and lower rates of series completion.

An important limitation of this study is that our data relies on self-report for vaccination status instead of documented medical records. The HPV vaccination often occurs during childhood. Thus, recall bias may be present, particularly in regard to respondents’ recollection of the number of doses of the vaccine received. Furthermore, respondents may not have been in the military health care system at the time of vaccination and thus reported vaccination rates may not be an accurate representation of military vaccination rates.

CONCLUSION

Our study shows that the HPV vaccination rate in vaccine eligible veteran men is higher compared to civilian men, a parallel to prior studies comparing female military members with civilians with military women having higher vaccination. The overall vaccination rate was 16.5% (95% CI, 14.3%–17.6%) among the vaccine eligible group. The vaccination rate among veteran men was 25.3% (95% CI, 18.8%–33.3%) compared to 15.9% (95% CI, 14.3%–17.6%) in civilian men (p < 0.01). Improvements have been made in HPV vaccination rates, however there is still vast room for improvement and current vaccination rates do not reach the U.S. Department of Health and Human Services’ Healthy People goal of 80%. Education and outreach programs are needed to increase public awareness of the HPV vaccine and the reduced incidence of HPV associated cancers in vaccinated individuals. Physician awareness of vaccination recommendations and incorporation of the vaccine as part of routine primary and preventative care are other potential areas for improvement in cancer prevention by HPV vaccination.

Presentations

Presented as a poster at the 2016 Military Health System Research Symposium.

FUNDING

This supplement was sponsored by the Office of the Secretary of Defense for Health Affairs.

References

Author notes

The views expressed in this paper are those of the authors and do not necessarily represent the official position or policy of the U.S. Government, the Department of Defense, or the Department of the Army/Navy.