Natalia Mendoza, MD,1 Paul O. Hernandez, BA,2 Stephen K. Tyring, MD, PhD1,3

1Center for Clinical Studies, Houston, TX, USA
2University of Texas School of Medicine at San Antonio, San Antonio, TX, USA
3Department of Dermatology, University of Texas Health Science Center at Houston, Houston, TX, USA

Human papillomavirus (HPV) has a predilection for infecting epidermal and mucosal surfaces such as those of the anogenital region. HPV causes substantial pre-malignant, malignant, and benign disease in both women and men, ranging from cervical, vulvar, penile, and anal cancers to condyloma acuminata (genital warts). Although HPV vaccination is becoming more common, infection rates remain high in both genders. Perception of HPV vaccine has largely centered on its ability to prevent cervical cancer in women, though indication for its use in men is expanding. The benefits to men include prevention of genital warts and, more recently, regulatory approval was expanded in the US for prevention of anal cancer. Herein, we review HPV vaccine with a focus on its new indication in men and existing controversies.

Key Words:
cancer, HPV, human papillomavirus, vaccine, warts, Gardasil®, Cevarix®


Genital human papillomavirus (HPV) is the most common sexually transmitted infection (STI) in the US.1 An estimated 20 million Americans are currently infected, with 6.2 million new cases occurring each year in people 14-44 years of age. Seventy-four percent of new cases occur in persons aged 15-24 years, and it is suggested >80% of sexually active women will acquire genital HPV by age 50. The majority of infections are asymptomatic and self-limited; however, persistent HPV infection with an oncogenic type can cause cervical cancer. HPV infection is also common among men. Approximately 1 million American men have genital warts caused by HPV, with 2 of every 1,000 men newly diagnosed.2

More than 130 HPV types have been identified, with greater than 40 causing genital infection. Genital HPV is divided into two groups based on potential to cause cancer: high-risk or oncogenic types and low-risk or nononcogenic types. High-risk types (such as 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 68, 69, and 73) can cause low-grade and high-grade cervical cell abnormalities as well as anogenital carcinoma. Together HPV-16 and 18 account for about 70% of cervical cancers.3

Low-risk types (mainly 6 and 11) cause most (90%) of the genital warts in males and females, recurrent respiratory papillomatosis, and nasopharyngeal papillomas, as well as low-grade disease of the cervix in women.2

HPV Vaccines

Two HPV vaccines are currently available in the US, quadrivalent (Gardasil®) and bivalent (Cevarix®) vaccines. The Food and Drug Administration (FDA) approved the quadrivalent vaccine in 2006 and bivalent vaccine in 2009.2

The quadrivalent vaccine is composed of four HPV type-specific virus-like particles (VLPs) prepared from the capsid protein of HPV-6, 11, 16, and 18 combined with aluminum adjuvant. This vaccine is recommended for females 9-26 years (in Canada the approved indication includes girls and women 9-45 years of age) and is administered intramuscularly according to a 3-dose schedule at 0, 2, and 6 months. The bivalent vaccine is composed of two VLPs of HPV-16 and 18 and is recommended for females 10-25 years through intramuscular injection according to a 3-dose schedule at 0, 1, and 6 months.2,4

The efficacy of quadrivalent vaccine is well established. In a per-protocol analysis (two Phase III trials), vaccine efficacy was 100% (95% CI, 80.9-100) for prevention of HPV-16 or 18 related cervical intraepithelial neoplasia (CIN) grades 2/3. In Protocol 013, which included 5,442 females aged 16-23 years, vaccine efficacy was 100% (95% CI, 89.5-100) for prevention of any grade CIN related to the vaccine types. The three studies (Protocol 007, 013, and 015) demonstrated vaccine efficacy of 98.9% (95% CI, 93.7-100) for prevention of HPV-6, 11, 16, and 18 related genital warts and 100% (95% CI, 55.5-100) for prevention of HPV-16 or 18 related vulvar intraepithelial neoplasia (VIN) 2/3 or vaginal intraepithelial neoplasia (VaIN) 2/3.5,6

The efficacy of bivalent vaccine is also well established. In a Phase III trial, which included 18,644 females aged 15-25 years, perprotocol cohort vaccine efficacy was 98.1% (96.1% CI, 88.4-100) for prevention of HPV-16 or 18 related CIN 2/3.7

New Indications

Although < 25% of all HPV-related cancers occur in men, specific groups, such as men who have sex with men, have significantly higher rates of HPV-related diseases, including anal cancer. HPV- 16 and 18 cause approximately 90% of anal cancers. Around 340,000 new cases of genital warts are reported in the US each year.8 In 2009, the FDA approved the quadrivalent vaccine for prevention of genital warts in young men. The Advisory Committee on Immunization Practices (ACIP) recommended permissive use but not routine use of the vaccine for males aged 9-26 years.9 More recently, regulatory approval was expanded in the US for prevention of anal cancer.

Recent data has demonstrated the quadrivalent vaccine to be effective in preventing anal intraepithelial neoplasia in males. A randomized, placebo-controlled, double-blind study conducted by Guiliano et al.10 included 4,065 males aged 16-26 years from 71 sites throughout 18 countries. Of these participants, 3,463 were heterosexual. At screening, subjects who had clinically detectable anogenital warts or genital lesions suggestive of existing HPV infection were excluded from the study. The participants were followed for 2.9 years.

Guiliano’s study showed prophylactic administration of quadrivalent vaccine to be efficacious in the prevention of genital lesions associated with HPV-6, 11, 16, and 18 in males aged 16-26 years. In the intention-to-treat population, vaccine efficacy was 65.5% (95% CI, 45.8-78.6) for prevention of vaccine type lesions and 60.2% (95% CI, 40.8-73.8) for prevention of any external genital lesion regardless of HPV type. When the per-protocol population was analyzed, vaccine efficacy for prevention of external genital lesions related to HPV-6, 11, 16, and 18 was 90.4% (95% CI, 69.2-98.1) and the efficacy against condyloma acuminata was 89.4% (95% CI, 65.5-97.9). No cases of PIN (penile, perianal, or perineal intraepithelial neoplasia) lesions were observed in the perprotocol vaccine group, however, this finding was not statistically significant in the study. Limitations of the study include the narrow age-range of the subjects and the relatively short followup period. Additionally, subjects had no more than five lifetime sexual partners, which could result in overrepresentation of subjects with a low likelihood of HPV exposure at baseline and subsequent exposure.10


Several questions have arisen concerning the use of HPV vaccine in females, which have further expanded with approval of the vaccine for males.

Will the vaccine prevent not only genital lesions, but also cervical and anal cancer and ultimately death?
An answer to this question will likely depend on decades of observation. However, benefits of the quadrivalent and bivalent vaccines have been consistently reported. HPV vaccine also has other early benefits. As reported in end-of-study data from Phase IIB and Phase III (FUTURE I and II) trials, vaccination in the negative to 14 HPV types population reduced the proportion of women who experienced a cervical therapy by 42% (95% CI, 28-54), which may reduce adverse pregnancy outcomes related to these procedures.11 HPV vaccine may also reduce the number of preterm deliveries due to cervical therapies.12

The probability of infection with HPV-6, 11, 16, and 18 in young women pre-sexual debut is very low, however, almost all women will come into contact with at least one type with only 0-4 sexual partners, thus, almost all young women may benefit from the vaccine. Studies have also shown that in women with evidence of current infection with at least one HPV vaccine type, quadrivalent vaccine may prevent disease caused by the remaining nonexposed vaccine types. Further, in women with cleared infections by an HPV vaccine type, quadrivalent vaccine has been shown to prevent recurrent disease caused by the same type.13,14

Australia is the first country to mount a fully funded HPV immunization program for all females 12-26 years of age. Within the first two years the country witnessed a 59% (95% CI, 54-61) reduction in genital warts in this age group of females, with the proportion of women diagnosed declining from 11.7% to 4.8%. In heterosexual males aged 12-26 years, a 39% (95% CI, 33-46) reduction in men diagnosed with genital warts from 17.3% to 10.5% was observed within the same two-year period. This finding in men is suggestive of herd immunity attributable to reduced exposure to HPV in vaccinated women.15

How long will protection conferred by the vaccine last?
Antibody titers reach their peak after the third dose, then decline gradually until month 24 and remain higher than those naturally infected. Phase IIB trials showed complete protection for the monovalent HPV-16 vaccine after 9.5 years, 6.4 years for the bivalent vaccine, and 4 years for the quadrivalent vaccine.16 HPV vaccine follow-up continues, with recent data indicating a rapid and strong anamnestic response induced by a fourth dose of HPV vaccine 6.8 years after the initial 3-dose vaccination course; all subjects demonstrated an approximate eight-fold increase in HPV-16 and 18 antibody titers 7 days after the fourth dose and a >16-fold increase after 1 month.17

Since most HPV infections are easily cleared by the immune system, how will vaccination affect natural immunity against HPV, and with what implications?
Although most HPV infections are easily cleared by the immune system, interim lesions represent a substantial burden on the health care system and can cause psychosexual distress in patients. As well, persistent infections have significant implications as a cause of cervical cancer. Antibody response to HPV, in general, is specific for the HPV type; however, cross-reactivity has been noted. Recent studies suggest that the quadrivalent vaccine may also provide cross-protection against HPV strains not contained in the vaccine, but are closely related.18,19 Notwithstanding, the durability of immunity and the importance of these findings remain to be established.

Will type replacement be seen?
With the introduction of HPV vaccines, “type replacement” is a concern. Type replacement is a viral population dynamics phenomenon defined as elimination of some types causing an increase of others. It occurs when partial competition exists among different types during natural infection and the vaccine does not provide cross-protection against competing types. In HPV, natural competition does not appear to exist, therefore type replacement is unlikely.4

How will the vaccine affect other oncogenic strains of HPV?
There is risk of change in population dynamics for existing HPV types and viral mutations may occur to generate new variants that are equally oncogenic but not recognized by vaccine-induced antibodies. However, HPV uses host cell DNA polymerases, and thus, has a very slow mutation rate, suggesting this risk is very low.4

How will vaccination affect screening practices?
Cytological screening practices should not be modified since the endpoint of the vaccine (cervical cancer) may take decades before incidence change can be measured. It has been suggested by HPV vaccine biologic models that the vaccine may increase the screening intervals.4 Positive predictive value will drop, making viral testing more appealing.

Other Vaccine Benefits

All HPV lesions, including genital warts, are associated with significant physical and psychological morbidity, high treatment failure and recurrence rates, as well as substantial cost.

The incidence of HPV infection is similar among both males and females, however, prevalence of infections is higher in males. Differences in immune response to HPV between genders have been described. A US study found HPV-seropositivity was higher in females than males (17.9% vs. 7.9%, respectively).20 The higher prevalence of HPV infections in men may be explained in part by the lower immune response to natural infection.

The ACIP recommends routine vaccination of females aged 11-12 years (the vaccination series may be started as early as 9 years) and catch-up vaccination for females aged 13-26 years. Similarly, the European Centre for Disease Control and Prevention recommends that the primary target population for HPV vaccination should be young girls before they become sexually active, with catch-up vaccination administered in older girls and young women. These measures will likely accelerate the public health impact of vaccination while also increasing short-term benefits.


HPV vaccination represents an important approach in cancercontrol strategies aimed at reducing the global incidence of cervical cancer. Routine vaccination of girls is already recommended and catch-up immunization programs have also been instituted for older girls not yet vaccinated in order to complete the schedule. The increasing prevalence of HPVrelated cancers in males coupled with a lack of anal cancer screening underscores the importance of routine vaccination of boys, not only to benefit the boys themselves but also to reduce transmission to unvaccinated girls, thus further widening the impact of HPV vaccination.


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