• Open Access

Efficacy of quadrivalent human papillomavirus (types 6, 11, 16 and 18) vaccine (GARDASIL) in Japanese women aged 18–26 years

Authors


To whom correspondence should be addressed.

E-mail: yohiyuki_tanaka@merck.com

Abstract

A randomized double-blind placebo-controlled phase II trial was conducted to evaluate the efficacy of a prophylactic quadrivalent vaccine targeting the human papillomavirus (HPV) types most frequently associated with cervical cancer (types 16/18) and genital warts (types 6/11) in Japanese women aged 18–26 years. Participants were randomly assigned to either quadrivalent HPV (types 6/11/16/18) L1 virus-like particle vaccine (GARDASIL) (= 509) or placebo (= 512). Participants underwent regular gynecological examinations, cervicovaginal sampling for HPV DNA, testing for serum neutralizing antibodies to HPV and Papanicolau testing. The primary end-point was the combined incidence of persistent infection with HPV types 6, 11, 16 or 18 and cervical or external genital disease (i.e. cervical intraepithelial neoplasia, cervical cancer or external genital lesions related to HPV 6, 11, 16 or 18. Primary analyses were done per protocol. Combined incidence of persistent infection or disease with HPV 6, 11, 16 or 18 fell by 87.6% (95% confidence interval [CI], 59.2–97.6; P < 0.001), with HPV 6 or 11 by 73.1% (95% CI, −1.1–97.3; P = 0.0756) and with HPV 16 or 18 by 94.5% (95% CI, 65.2–99.9; P < 0.001) in those assigned vaccine compared with those assigned placebo. The median duration of follow up after month 7 in subjects was 23 months. In addition, the vaccine was well tolerated in Japanese women aged 18–26 years. Quadrivalent HPV vaccine could significantly reduce the acquisition of infection and clinical disease caused by HPV types 6, 11, 16 and 18.

Human papillomavirus (HPV)-related genital warts are considered to be the most common sexually transmitted disease. Transmission is mainly via transfer of viral particles through sexual intercourse, although evidence exists to support genital to genital, manual to genital and oral to genital transmission.[1-3] HPV 6 and HPV 11 are found in over 90% of anogenital warts cases.[4] The lesions may appear over the posterior introitus, the labia majora and minora, vagina and anus. Anogenital warts are a reportable disease that must be reported to Japan's Infectious Disease Surveillance Center.[5] Over the past 10 years, the annual average number of cases of condyloma acuminata reported in Japan was 5955, with men having a consistently higher number of reported cases than women. Condyloma acuminata cases are reported in men of all ages, although the majority occurs between the ages of 20 and 40 years.[5] Treatments for genital warts in Japan include ointments (5-FU, bleomycin, imiquimod), surgical treatments (laser ablation), electronic iron and liquid nitrogen. Unfortunately, some of these treatments can be disfiguring. No treatment exists that eliminates the virus from the body, therefore the rate of recurrence is high (10–34%).[6]

In addition to leading to genital warts, infection with HPV is known to lead to cervical cancer. Human papillomavirus has been detected in 99.7% of patients with cervical cancer and HPV infection is considered to be a necessary prerequisite of the disease.[7] Among gynecological malignancies, the incidence of cervical cancer is second only to breast cancer worldwide. It is newly diagnosed in approximately half a million women per year and accounts for approximately one-quarter of a million deaths per year.[8]

Approximately 80% of patients with newly diagnosed cervical cancer live in developing countries.[9] The increased incidence of the disease in these parts of the world is likely related to their lack of organized Papanicolau (Pap) test screening programs. In Japan, approximately 10 000 women are diagnosed with cervical cancer every year and approximately 3500 women die of the disease annually.[10] Recent epidemiological data suggests that the proportion of mortality and morbidity from cervical cancer is rising in younger women when compared with older cohorts.[11, 12] Much effort has been made to investigate HPV-type specific prevalence among Japanese women with cervical cancer. A meta-analysis demonstrated that HPV16 and 18 were the most common types and together were associated with 58.8% of cervical cancer in Japan.[13] Based on a recent report, approximately 67.1% of cervical cancers in Japan are considered to be related to HPV types 16 and 18.[14] In addition, HPV infection is seen as a very important risk factor for vulvar, vaginal and anal cancers.

Thus, cervical cancer, vulvar cancer, vaginal cancer and genital warts have now been recognized as lesions related to an infection that could be primarily prevented by vaccination against the HPV types causing those lesions. For this reason, development of HPV vaccines is a major target for current HPV research.

Quadrivalent HPV vaccine (qHPV) is an aluminum-adsorbed recombinant polypeptide vaccine that contains purified genetically engineered virus-like particle (VLP) L1 capsid polypeptides for HPV 6, 11, 16 and 18 produced in Saccharomyces cerevisiae.[15] In studies outside of Japan, in 9–26-year-old female subjects, administration of qHPV vaccine was shown to be generally well tolerated and to generate vaccine HPV type-specific neutralizing antibodies. In addition, qHPV vaccine was shown to significantly reduce the incidence of persistent HPV infection and genital disease in women aged 18–26 years. Recently, the interim analysis of a long-term follow-up study in Nordic countries showed a trend toward continued protection in vaccine recipients for up to 7 years after vaccination based on our unpublished data.

The present study was designed to investigate the combined incidence of infection with HPV type 6, 11, 16 and 18, as well as the incidence of cervical or external genital disease in Japanese women aged 18–26 years. In addition, anti-HPV 6, 11, 16 and 18 titers were analyzed following vaccination. Safety and tolerability data were also collected following the administration of qHPV vaccine.

Participants and Methods

A phase II randomized, multicentre, double-blind placebo-controlled trial of a qHPV (types 6, 11, 16 and 18) L1 VLP vaccine (qHPV) was conducted. Japanese women (n = 1030) aged 18–26 years were recruited. The study enrolled healthy women who were not pregnant, had no previous abnormal Pap smears and reported a lifetime history of four or fewer male sex partners. The present study did not exclude women with previous HPV infection. Participants were required to use effective contraception during the vaccination phase. The qHPV vaccine was a mixture of four recombinant HPV type-specific VLP (Merck Research Laboratories, West Point, PA, USA) consisting of the L1 major capsid proteins of HPV 6, 11, 16 and 18 produced in Saccharomyces cerevisiae. The four VLP types were purified and adsorbed onto amorphous aluminium hydroxyphosphate sulfate adjuvant: 20 μg of HPV type 6, 40 μg of HPV type 11, 40 μg of HPV type 16 and 20 μg of HPV type 18, with 225 μg aluminum adjuvant. The placebo consisted of the same adjuvant without VLP and was visually indistinguishable from vaccine. A 0.5 mL vaccine or placebo was given by intramuscular injection at day 1, month 2 and month 6. Temperatures were also recorded orally every day in the evening for 4 days after vaccination and the participant was to note adverse events by standard diary card for 15 days after vaccination. Gynecological examination was done at day 1 and at months 7, 12, 18, 24 and 30. A ThinPrep Pap test (Cytyc, Boxborough, MA, USA) and external genital and cervical swabs for PCR analysis of HPV were obtained from all participants at day 1 and at months 7, 12, 18, 24 and 30. Biopsy samples of external genital lesions identified during the study were taken and serum samples were obtained at day 1 and months 2, 3, 7, 18 and 30.

The present study was conducted in accordance with the ethical principles that have their origin in the Declaration of Helsinki. Moreover, it was conducted in accordance with the protocol agreed to by investigators and the sponsor and approved by each Institutional Review Board, the standards provided by Article 14 Paragraph 3 and Article 80-2 of the Pharmaceutical Affairs Law and the Good Clinical Practice (GCP) Ordinance.[16] All individuals, or their parents or legal guardians, gave written informed consent after review of the protocol procedures.

The aim of the present study was to assess the composite primary end-point of persistent infection (with HPV 6, 11, 16 or 18), cervical and external genital disease (related to HPV 6, 11, 16 or 18) compared with placebo. Women with persistent infection were defined as those who had the same vaccine HPV-type DNA in cervicovaginal samples obtained at month 7 after first vaccination or placebo as those obtained from two or more consecutive visits (required to be 4 months or more apart unless at least one tissue sample was diagnosed as cervical disease by a panel of pathologists). HPV-associated disease was defined as a tissue sample diagnosed as cervical intraepithelial neoplasia (CIN), vulval intraepithelial neoplasia (VIN), vaginal intraepithelial neoplasia (VaIN), external genital warts or cervical, vulval or vaginal cancer with vaccine HPV-type DNA detected in tissue from cervicovaginal samples obtained at the visit or the biopsy visit.

All Pap tests and histological assessment were done in the setting of the study. Pap tests were reported in accordance with the Bethesda 2001 System.[17] Women underwent colposcopy if they were diagnosed with atypical squamous cells (in which high-grade squamous epithelial lesions could not be excluded), low-grade squamous intraepithelial lesions, high-grade squamous intraepithelial lesions or atypical glandular cells. After the release of the American Society for Colposcopy and Cervical Pathology Biopsy Guidelines for management of atypical squamous cells of undetermined importance,[18] residual liquid from these Pap tests was analysed by Hybrid Capture II (Digene, Gaithersburg, MD, USA) testing. Patients with a positive result on either low- or high-risk HPV probes underwent colposcopy. At colposcopy, biopsy samples of discrete abnormalities were taken with separate instruments and were processed separately for histopathological analysis to avoid HPV contamination. A sample of the same lesion or a sample adjacent to the biopsied lesion was submitted for HPV typing. Biopsy samples were processed and read by a central laboratory (Diagnostic Cytology Laboratories, Indianapolis, IN, USA) for medical management. End-point assignment was done by use of consensus diagnoses from a panel of pathologists who were blinded to the central laboratory diagnoses, vaccination group and HPV status.[19] Swabs, biopsy samples and, later, thin tissue sections cut adjacent to sections used for histopathological analysis were used to detect HPV DNA with primers specific for HPV 6, 11, 16 or 18. Serum concentrations of antibodies to HPV 6, 11, 16 and 18 were measured with a competitive immunoassay (Luminex Corporation, Austin, TX, USA).[20] Antibody titers were determined in a competitive format, that is, known, type-specific phycoerythrin-labelled, neutralising antibodies[21, 22] compete with serum antibodies from the participant for binding to conformationally sensitive, single, dominant neutralising epitopes on VLP.

Statistical methods

The present study was designed to compare qHPV vaccine with its matching placebo using the double-blind method. To maintain blinding, a randomization schedule was prepared and retained. Subjects were allocated in a 1:1 ratio to qHPV vaccine or placebo. The person responsible for allocation of the investigational product prepared the randomization schedule for sets of 10 subjects (five subjects in each group), generated by the permuted block method. The prepared randomization schedule was sealed with other corresponding randomization listings and retained strictly until unblinding by the Center for Patients Allocation (Tokyo, Japan). Primary efficacy analyses were done in the HPV 6, 11, 16 and 18 per-protocol efficacy cohorts, which consisted of women who were naive for the relevant HPV type at enrollment, remained free of infection with the same vaccine HPV type through completion of the vaccination regimen, had all three doses of vaccine or placebo and did not violate the protocol. Counting of efficacy cases started after month 7. To test the efficacy of the qHPV vaccine against persistent infection or disease associated with HPV 6, 11, 16 or 18, a one-sided test of the null hypothesis that the vaccine efficacy was less than or equal to 0 versus the hypothesis that vaccine efficacy was more than 0 at the α = 0.025 level was done. Thus, rejection of the null hypothesis required the lower bound of the two-sided 95% confidence interval (CI) for vaccine efficacy to exceed 0. An exact conditional procedure was used to assess vaccine efficacy with the assumption that the number of cases in the vaccine and placebo groups are independent Poisson random variables. Individual follow up was calculated as the number of person–years between the specified start time and the final visit date, the date the participant became a case (i.e. developed an end-point) or the date the participant underwent definitive treatment (cervical end-points only). If a woman developed more than one end-point, her date of becoming a case was the date when the first end-point was detected. Overall, 17 women with the composite end-point of persistent infection or diseases associated with the vaccine HPV types were needed for the study to have 94% power to declare the vaccine efficacious with a one-sided α = 0.025, assuming a true vaccine efficacy of 85%. Therefore, enrollment of approximately 500 participants in the placebo and qHPV vaccine groups was needed. Immunogenicity was measured in a per-protocol immunogenicity cohort, defined as members of the per-protocol efficacy cohort who were vaccinated and who had serum samples obtained during the protocol-specified time frames, irrespective of HPV infection or disease status after month 7. Wilcoxon rank sum test was used to assess the difference in immune response at month 7 between the vaccine and placebo groups. All subjects who received at least one study vaccination and had follow-up data were included in the analysis of safety. Injection-site and systemic adverse experiences were summarized and compared between the vaccination groups.

Results

Women were randomly assigned to qHPV vaccine (n = 509) or placebo (n = 512) groups (Fig. 1). Subject characteristics by vaccination group at enrollment can be seen in Table 1. Four hundred subjects were included in the per-protocol efficacy analyses for HPV types 6 and 11; 371 subjects were included in the analysis for type 16 and 403 subjects were included in the analysis for type 18 (Tables 2, 3). Four hundred and eighty women assigned qHPV vaccine and 468 assigned placebo were included in the safety analyses (Table 4). The main reasons for exclusion from the per-protocol cohort were seropositivity to a vaccine HPV type at day 1 or presence of HPV 6, 11, 16 or 18 DNA before completion of the vaccination regimen. Baseline seropositivity to vaccine HPV types can be seen in Table 5, as can the baseline presence of HPV 6, 11, 16 or 18 DNA in swab samples. Primary efficacy analyses were performed in the per-protocol efficacy cohort (Table 2). The median follow-up time after month 7 was 22.7 and 22.8 months for the vaccine and placebo groups, respectively. The combined incidence of persistent HPV 6, 11, 16 or 18 infection or associated genital disease was 0.4 and 3.1 per 100 person–years in the vaccine and placebo groups, respectively. The incidence decreased by 87.6% (95% CI, 59.2–97.6) in women assigned vaccine compared with those assigned placebo (Table 2). The incidence of genital disease alone was 0.0 and 0.6 per 100 person–years in the vaccine and placebo groups, respectively. The prophylactic efficacy against disease was 100% (95% CI, −10.4–100.0%) (Table 3). The disease that was seen (CIN1 and CIN2) was diagnosed in the placebo group.

Table 1. Characteristics by vaccination group at enrollment
CharacteristicsVaccine (= 509)Placebo (= 512)
  1. ASC-H, atypical squamous cells cannot exclude HSIL; ASC-US, atypical squamous cells of undetermined significance; HSIL, high grade squamous intraepithelial lesion; LSIL, low grade squamous intraepithelial lesion; SD, standard deviation.

Age (years)
 Mean (SD)22.7 (2.1) 22.9 (2.1)
Lifetime number of sexual partners
 03323
 18681
 299100
 3155139
 4136169
Median (range)3 (0–4)3 (0–4)
Papanicolau test
 Normal 454444
 ASC-US 1624
 ASC-H 62
 HSIL 33
 LSIL 2634
 Unsatisfactory 45
Contraceptive use (>10%)
 Male condom 376370
 Abstinence 322341
 Oral contraceptives/combination 200214
 Withdrawal 8380
Table 2. Efficacy of quadrivalent vaccine against persistent infection or disease associated with HPV 6, 11, 16 or 18 in the per-protocol population
Types of persistent infection and genital diseaseVaccinePlaceboEfficacy estimate (%)§95% CIP-value*
n No. casesPerson–years at riskIncidence rate (/100 person–years at risk) n No. casesPerson–years at riskIncidence rate (/100 person–years at risk)
  1. *P-value for one-sided test. †The per-protocol population included all subjects who were not general protocol violators, received all three vaccinations within 1 year and were seronegative at day 1 and PCR negative day 1 through month 7 for the relevant HPV types. ‡Three events were observed in the vaccine group. Two were HPV 6-related persistent infection and one was HPV 18-related persistent infection. No disease case was observed in the vaccine group. §Observed efficacy was defined as the percentage reduction in risk of the given event in vaccine group relative to the placebo group. CI, confidence interval; HPV, human papillomavirus; n, number of subjects evaluable (i.e. number of subjects in the given population who also had at least one follow-up visit).

HPV 6-, 11-, 16- or 18-related4193776.40.442224769.13.187.659.2–97.6<0.001
HPV 6- or 11-related4002743.00.33767698.51.073.1−41.1–97.30.0756
HPV 6 related4002743.00.33767698.51.073.1−41.1–97.30.0756
HPV 11 related4000746.00.03760704.00.0NANANA
HPV 16- or 18-related4151771.90.141718763.82.494.565.2–99.9<0.001
HPV 16 related3710689.50.037811698.01.6100.059.7–100.0<0.001
HPV 18 related4031750.50.13967734.91.086.0−8.9–99.70.0329
Table 3. The composite incidences of HPV 6-, 11-, 16-, or 18- related genital disease (PPE population)
Types of genital diseaseVaccinePlaceboEfficacy estimate (%)95% CIP-value*
n No. casesPerson–years at riskIncidence rate (/100 person–years at risk) n No. casesPerson–years at riskIncidence rate (/100 person–years at risk)
  1. *P-value for one-sided test. †The per-protocol efficacy (PPE) population includes all subjects who were not general protocol violators, received all three vaccinations and were seronegative at day 1 and PCR negative day 1 through month 7 for the relevant HPV type(s). Counting of efficacy cases started after month 7. ‡Observed efficacy was defined as the percentage reduction in risk of the given event in vaccine group relative to the placebo group. A P-value < 0.025 (one-sided) corresponded to a lower bound of the CI for vaccine efficacy >0. CI, confidence interval; HPV, human papillomavirus; n, number of subjects evaluable (i.e. number of subjects in the given population who also had at least one follow-up visit after month 7).

HPV 6-, 11-, 16- or 18-related 4190780.80.04225789.60.6100.0−10.4–100.00.0321
HPV 6- or 11-related4000746.00.03761703.20.1100.0−3576.3–100.00.4852
HPV 6 related4000746.00.03761703.20.1100.0−3576.3–100.00.4852
HPV 11 related4000746.00.03760704.00.0NANANA
HPV 16- or 18-related4150773.30.04174780.40.5100.0−52.9–100.00.0673
HPV 16 related3710689.50.03783706.40.4100.0−147.9–100.00.1296
HPV 18 related4030751.90.03961743.00.1100.0−3754.0–100.00.4970
Table 4. Summary of clinical adverse experience (days 1–15 following any vaccination) (safety analysis population)
Types of adverse experienceVaccine (= 480)Placebo (= 468)
n % n %
  1. Vaccine-related adverse experiences are adverse experiences determined by the investigator to be possibly, probably or definitely drug related.

No adverse experience479.87516.0
One or more adverse experiences43390.239384.0
Injection-site adverse experiences40985.233872.2
Systemic adverse experiences21244.221145.1
Vaccine-related adverse experiences41786.934774.1
Vaccine-related injection-site adverse experiences40885.033872.2
Vaccine-related systemic adverse experiences6613.85311.3
Serious adverse experiences30.610.2
Serious vaccine-related adverse experiences00.000.0
Died00.000.0
Table 5. Composite sero- and PCR-status at day 1
 VaccinePlacebo
All HPV 6, 11, 16 and 18 negative
Serology435/509 (85.5)434/512 (84.8)
PCR438/487 (89.9) 445/492 (90.4)
Serology and PCR415/509 (81.5) 412/512 (80.5)
At least one type of HPV 6, 11, 16 or 18 positive
Serology74/509 (14.5)78/512 (15.2)
PCR49/487 (10.1)47/492 (9.6)
Serology or PCR94/509 (18.5)100/512 (19.5)
Figure 1.

Trial profile. GCP, good clinical practice; AE, adverse event.

Vaccine-induced immune responses were assessed in the HPV 6, 11, 16 and 18 per-protocol immunogenicity cohorts, which included 386, 386, 357 and 389 women assigned vaccine, respectively. An immune correlate of protection from HPV types contained in the vaccine has not yet been defined. Anti-HPV 6, 11, 16 and 18 Geometric Mean Titer (GMT) at month 7 in the qHPV vaccine group were 390.8, 579.8, 2396.4 and 369.0 mMU/mL, respectively. These values were significantly higher compared with those observed in the placebo group (P < 0.001 for each HPV type). The seroconversion rates of each vaccine HPV type (types 6, 11, 16 and 18) at month 7 in the qHPV vaccine group were 99.7%, 100%, 100% and 99.5%, respectively. These values were significantly higher compared with those observed in the placebo group (< 0.001 for each HPV type). Anti-HPV 6, 11, 16 and 18 GMT at 2 years after the completion of a three-dose regimen (month 30) in the qHPV vaccine group were 75.6, 99.9, 295.2 and 34.1 mMU/mL, respectively. These values were significantly higher compared with those observed in the placebo group (P < 0.001 for each HPV type). Hence, vaccine-induced GMT of antibodies were substantially higher in women assigned active vaccine than in those assigned placebo (Fig. 2). Although mean neutralizing antibody titers in those assigned qHPV vaccine started to decline after month 7, they remained above the titers recorded for women who received placebo at month 30 (Fig. 2).

Figure 2.

Change in serum antibody titers through month 30 (per protocol population).

Quadrivalent HPV vaccine was generally well tolerated (Table 4). The percentage of subjects with adverse events was higher in women given active vaccine compared with those given placebo. Pain was the most common injection site adverse event and headache the most common systemic adverse event. Most (>90%) adverse events were of mild or moderate intensity. Only one patient (in the vaccine group) discontinued the study, because of moderate pyrexia on day 1 following the initial vaccination. There were no vaccine-related serious adverse events.

Discussion

Over 26 000 subjects have been enrolled from five continents into clinical studies with qHPV vaccine. This includes two major randomized, double-blind, placebo-controlled trials (FUTURE I and FUTURE II).[23, 24] This has allowed investigation of the effects of race and region on the efficacy and safety of the qHPV vaccine. Importantly, subgroup analysis by race and region has demonstrated that the efficacy, immunogenicity and safety of qHPV vaccine was not different between each race and region.

We have shown that qHPV vaccine is efficacious against HPV types that cause cancer and genital warts in Japan by observing a combined primary end-point of both persistent infection and genital disease. Vaccine efficacy against this end-point was 87.6% in the per-protocol efficacy population. Furthermore, efficacy with regard to HPV types closely related to cervical cancer (types 16 and 18) was 94.5% in the per-protocol population. Analyses were also conducted in an intention-to-treat (ITT) population consisting of subjects who received at least one injection and had one or more follow-up visits after 1 month following the first injection regardless of initial serology and HPV PCR status. The per-protocol efficacy (PPE) population is different from the ITT population, in that subjects who were vaccine HPV-type PCR positive at day 1 were included. Therefore, the efficacy of the ITT population represented the general population of 18–26-year-old women. The efficacy of vaccine for composite end-point of HPV 6, 11, 16 or 18 persistent infection and genital disease in this population was 59.8% (95% CI, 36.1–75.4%), which was statistically significant. Vaccine efficacy against clinical disease associated with HPV 6, 11, 16 or 18 was 100% (Table 3). The point estimation for vaccine efficacy seen in the present study was slightly lower than that seen in FUTURE I and FUTURE II; however, this difference could be explained by smaller sample sizes in the Japanese study. In addition, the present study was not originally powered to assess vaccine efficacy for the disease end-points or for each HPV type separately. However, those results are generally comparable with overseas studies of qHPV vaccine. In addition, the present study demonstrated safety results consistent with those of FUTURE I and FUTURE II. Although syncope following HPV vaccination has been discussed in the literature, it was not reported in this Japanese study due to the relatively small sample size.

The distribution of HPV types differs greatly depending on the presence or absence of cervical lesions. The more severe the lesion, the more likely one is to be a carrier of HPV 16 and/or HPV 18.[24] A published meta-analysis[13] indicates that the rates of HPV 16 and 18 were 44.8% and 14.0%, respectively, in patients with HPV-related invasive cervical cancer. This is significant when one takes into consideration the data showing that approximately 67.1% of cervical cancers in Japan are related to HPV types 16 and 18.[14] The total rate of HPV 16 and 18 infections in HPV-related cervical cancer patients has been estimated to be 76.4% in North America and 73.8% in Europe. Based on these data, the prevalence of HPV 16- and 18-related invasive cervical cancer in Japan might be slightly lower than in the USA and Europe. However, the prevalence of HPV 16 and 18 infection was as high in Japan as in the USA and Europe.[13] In contrast, it is well known that other types of HPV also play important roles in cervical cancer development. If a vaccine that includes additional HPV types is developed, the prevention of cervical cancer could be further enhanced.

Vaginal and vulvar cancers are relatively rare cancers even within genital cancer. Vaginal cancer is closely associated with cervical cancer and it has been suggested that these cancers share a common etiology. According to data from the World Health Organization/Institut Català d'Oncologia HPV information center, the frequencies of detection of HPV 16 and 18 from vaginal cancer in Japan are 37.5% and 6.3%, respectively.[25] Also, HPV is often detected in vulvar cancer. The detection rates of HPV 16 and 18 from vulvar cancer in Japan are 14.3% and 4.8%.[25]

Even though the prophylactic efficacy and safety of the qHPV vaccine have already been proven, screening programs using Pap testing still play an important role in preventing cervical cancer. Pap testing reduces the incidence of cervical cancer by allowing for the detection and excision of precancerous lesions prior to the development of cancer. The HPV vaccination strategies do not fully replace Pap screening as the qHPV vaccine has shown no therapeutic effect and does not include all HPV types linked to cervical cancer.

There are several neutralization epitopes displayed by L1 VLP,[26] but the competitive Luminex bead assay used in the quadrivalent vaccine trials measures the antibody response to only one of these epitopes in contrast to the conventional ELISA, which measures total antibody (both neutralizing and non-neutralizing).[27] Therefore, the sensitivity of the competitive Luminex bead assay might be lower than other serological assays that can measure total antibodies against HPV like a conventional ELISA. As the baseline antibody level was used to define the PPE population, lower sensitivity of antibody detection might lead to contamination of previously HPV-infected subjects in the PPE population and might increase vaccine failure. Even when using the Luminex-based assay, results indicate that the qHPV vaccine was highly immunogenic in Japanese women. All women allocated to the vaccine group developed higher detectable neutralizing antibody responses to HPV at month 7 than those allocated to the placebo group. Because women are at risk of HPV infection for as long as they are sexually active, protection induced by a HPV vaccine must be long lived. At month 30, more than 91.8%, 97.5% and 99.1% of women were seropositive for HPV 6, 11 and 16, respectively. Fewer (59.3%) women had detectable neutralizing antibody responses against HPV 18 at month 30, although 84% had HPV 18 neutralizing antibody titers above the assay's lower limit of quantification. These trends are quite similar to the results seen in other qHPV clinical trials. In a study in which a subset of participants from the phase III trials were selected, HPV 18 antibody concentrations in approximately 40% of participants immunized with the qHPV vaccine fell to background levels over a 4-year period; however, efficacy against HPV 18-associated CIN 2/3, VIN 2/3, VaIN 2/3 and adenocarcinoma in situ remained at 100% irrespective of antibody level.[28] A recent report demonstrates that after 48 months, qHPV-vaccinated subjects who might no longer be detectable using competitive immunoassay possess detectable neutralizing antibodies by pseudovirion neutralization assay. These data support the observed sustained HPV 18 protection against persistent infection and disease with the absence of breakthrough cases in qHPV vaccines.[29]

The current emerging scientific evidence reveals that there is no relationship between prophylactic effect and antibody titer thus far. In addition, longer follow-up studies with qHPV vaccine are ongoing to assess the duration of efficacy. However, the persistence of antibody might not be the issue of relevance for protection from HPV. An overseas study in 552 women aged 16–23 years indicates that the qHPV vaccine induces robust immune memory.[30] Following a three-dose regimen, serum anti-HPV levels declined post-immunization, reaching a plateau at 24 months. In a subset of women followed for 60 months, serum anti-HPV levels rose dramatically 1 week and 1 month after administration of a challenge dose of quadrivalent vaccine. Anti-HPV levels in these women were higher than those observed following the initial immunization series.[30]

Published literature suggests that the incidence of genital warts in Australia went down quickly and significantly after the introduction of the qHPV vaccine in 2007. Starting in April 2007, Australia made the HPV vaccine available to all girls in schools. In July 2007, it expanded the program to women under the age of 27 outside of schools. Before the vaccine was introduced, 15% of women treated at the Melbourne Sexual Health Centre had genital warts, but that rate has now declined to 6%.[31] This decline is thought to be this large because 70% of women under age 28 have been vaccinated, by far the highest coverage in the world. Another study in Australia demonstrated a decrease in the incidence of high-grade cervical abnormalities by 0.38% (95% CI, 0.61–0.16) in girls younger than 18 years.[32] This decrease was progressive and significantly different to the linear trend in incidence before introduction of the vaccination (incident rate ratio, 1.14 [95% CI, 1.00–1.30]; P = 0.05). No similar temporal decline was recorded for low-grade cervical abnormalities or in older age groups.[32] Considering the evidence, universal HPV vaccination is likely to be effective in reducing the population prevalence of genital warts, cervical cancer and other HPV 6, 11, 16 and 18-related diseases. The expectation that the vaccine will reduce cervical cancer rates, the fact that HPV infection affects most women and the lack of an effective means to prevent HPV infection in sexually active people lend support to the vaccination of preadolescents.

This is the first study in Japan showing that a HPV 6, 11, 16 and 18 vaccine was generally well tolerated, induced high titers of serum neutralizing antibodies to HPV types and effectively prevented acquisition of infection and clinical disease caused by common HPV types in Japan. Additionally, this study could provide valuable epidemiological information regarding HPV infection and disease development caused by HPV in Japan.

Acknowledgments

We thank Scott Vuocolo for critical review and language editing of this manuscript. We also thank Shinichi Kanazu, Nobuyoshi Hazumi and Akira Wakana for their support in preparing this manuscript and all of the participant study sites as follows: SEIKO-KAI NS Clinic, SEIWA-KAI Iesaka Ladies Clinic, Medical Corporation Shinanokai Shinanozaka Clinic, KEIKO-KAI P-One Clinic, Nittazuka Iryo-Fukushi Center Fukui General Hospital, Ikebukuro Clinic, Clinic of Japan Family Planning Association, Women's Clinic Minami Aoyama, Mori Ladies Clinic, SHINYU-KAI Asty Ladies Clinic, Tabata Hospital, Miyakawa Clinic, CHISEN-KAI Kano Hospital and Kyoundo Hospital of Sasaki Foundation.

Disclosure Statement

H.Y. and K.N. received lecture, advisory and travel fees from MSD K.K. Y.T. and K.E. are employees of MSD K.K., a group of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Whitehouse Station, NJ, USA.

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