Public health paradoxes and the epidemiological impact of an HPV vaccine

High Prevalence of HPV 51 in an Unvaccinated Population and Implications for HPV Vaccines

Human papillomavirus (HPV) is detected in 99.7% of cervical cancers. Current vaccines target types 16 and 18. Prior to vaccination implementation, a prospective cohort study was conducted to determine baseline HPV prevalence in unvaccinated women in Wales; after HPV16 and HPV18, HPV 51 was found to be most prevalent. This study aimed to re-assess the unexpected high prevalence of HPV 51 and consider its potential for type-replacement. Two hundred HPV 51 positive samples underwent re-analysis by repeating the original methodology using HPV 51 GP5+/6+ PCR-enzyme immunoassay, and additionally a novel assay of HPV 51 E7 PCR. Data were correlated with age, social deprivation and cytology. Direct repeat of HPV 51 PCR-EIA identified 146/195 (75.0%) samples as HPV 51 positive; E7 PCR identified 166/195 (85.1%) samples as HPV 51 positive. HPV 51 prevalence increased with cytological grade. The prevalence of HPV 51 in the pre-vaccinated population was truly high. E7 DNA assays may offer increased specificity for HPV genotyping. Cross-protection of current vaccines against less-prevalent HPV types warrants further study. This study highlights the need for longitudinal investigation into the prevalence of non-vaccine HPV types, especially those phylogenetically different to vaccine types for potential type-replacement. Ongoing surveillance will inform future vaccines.

Human papillomavirus seroprevalence in pregnant women following gender-neutral and girls-only vaccination programs in Finland: A cross-sectional cohort analysis following a cluster randomized trial

BACKGROUND

Cervical cancer elimination through human papillomavirus (HPV) vaccination programs requires the attainment of herd effect. Due to its uniquely high basic reproduction number, the vaccination coverage required to achieve herd effect against HPV type 16 exceeds what is attainable in most populations. We have compared how gender-neutral and girls-only vaccination strategies create herd effect against HPV16 under moderate vaccination coverage achieved in a population-based, community-randomized trial.

METHODS AND FINDINGS

In 2007-2010, the 1992-1995 birth cohorts of 33 Finnish communities were randomized to receive gender-neutral HPV vaccination (Arm A), girls-only HPV vaccination (Arm B), or no HPV vaccination (Arm C) (11 communities per trial arm). HPV16/18/31/33/35/45 seroprevalence differences between the pre-vaccination era (2005-2010) and post-vaccination era (2011-2016) were compared between all 8,022 unvaccinated women <23 years old and resident in the 33 communities during 2005-2016 (2,657, 2,691, and 2,674 in Arms A, B, and C, respectively). Post- versus pre-vaccination-era HPV seroprevalence ratios (PRs) were compared by arm. Possible outcome misclassification was quantified via probabilistic bias analysis. An HPV16 and HPV18 seroprevalence reduction was observed post-vaccination in the gender-neutral vaccination arm in the entire study population (PR16 = 0.64, 95% CI 0.10-0.85; PR18 = 0.72, 95% CI 0.22-0.96) and for HPV16 also in the herpes simplex virus type 2 seropositive core group (PR16 = 0.64, 95% CI 0.50-0.81). Observed reductions in HPV31/33/35/45 seroprevalence (PR31/33/35/45 = 0.88, 95% CI 0.81-0.97) were replicated in Arm C (PR31/33/35/45 = 0.79, 95% CI 0.69-0.90).

CONCLUSIONS

In this study we only observed herd effect against HPV16/18 after gender-neutral vaccination with moderate vaccination coverage. With only moderate vaccination coverage, a gender-neutral vaccination strategy can facilitate the control of even HPV16. Our findings may have limited transportability to other vaccination coverage levels.

TRIAL REGISTRATION

ClinicalTrials.gov number NCT00534638, https://clinicaltrials.gov/ct2/show/NCT00534638.

Knowledge, Attitude, and Barriers Towards Human Papillomavirus (HPV) Vaccination Among Youths of Karachi, Pakistan

Introduction Human papillomavirus (HPV) is the most common infection of the reproductive tract. The introduction of HPV vaccines by WHO aims to reduce the incidence of cervical cancer. Pakistan lacks an effective nationwide HPV vaccination program, thereby making HPV a major threat. In this study, we aimed to assess the knowledge of HPV vaccination in Pakistan and to determine the barriers against it. Methods A cross-sectional study was conducted in Karachi, Pakistan, between April and May 2019. A convenience sampling technique was implemented using a self-administered questionnaire, which was filled by individuals aged 18-26. The questionnaire assessed the knowledge regarding HPV and also evaluated the attitude and acceptability amongst these individuals towards the vaccine. Data were analyzed using Statistical Package for Social Sciences (SPSS), version 20.0. Results The majority of the participants belonged to the monthly household income range of 200,000 rupees and above, which was labeled as the high-income category (n=158, 39.5%). Out of the 18 people who were vaccinated, eight belonged to the aforementioned category. Of these 18, nearly two-thirds (n=11, 61.1%) had gotten vaccinated upon the recommendation of their doctor. A statistically significant difference was found only between those currently enrolled in universities and previously vaccinated for HPV (p=.047). Nearly half of the responders perceived the vaccine to be time-consuming (n=167, 41.8%) and overpriced (n=187, 46.8%). Conclusion The vaccination rate is low in Karachi, Pakistan. Concentrated efforts involving the healthcare system should be made to raise awareness regarding HPV and its vaccine thereby reducing barriers to HPV prevention.

Gender-neutral vaccination provides improved control of human papillomavirus types 18/31/33/35 through herd immunity: Results of a community randomized trial (III)

With optimal strategy, human papillomavirus (HPV) vaccines have the potential to control HPV. We have assessed vaccine efficacy (VE), herd effect (HE) of HPV vaccination and overall protective effectiveness (PE) against high-risk HPV infections by HPV type and vaccination strategy in a community-randomized trial using the bivalent HPV16/18 vaccine. We randomized 33 communities to gender-neutral HPV vaccination (Arm A), HPV vaccination of girls and hepatitis B-virus (HBV) vaccination of boys (Arm B) and gender-neutral HBV vaccination (Arm C). Entire 1992-1995 male (40,852) and female (39,420) birth cohorts were invited, and 11,662 males and 20,513 females vaccinated with 20-30% and 45% coverage in 2007-2010. During 2010-2014, 11,396 cervicovaginal samples were collected from 13,545 18.5-year-old attendees. HPV typing was performed by a high-throughput PCR. VE was calculated for HPV vaccinated women and HE for non-HPV-vaccinated women, using the HBV vaccinated, for HE all non-HPV vaccinated, Arm C women as controls. PE was calculated as coverage rate-weighted mean of VE + HE. HPV16/18/45 and 31/33/35 VEs varied between 86-94% and 30-66%, respectively. Only the gender-neutral vaccination provided significant HEs against HPV18 (61%) and HPV31 (72%) in the 1995 birth cohort-increased HEs against HPV33 (39%) and HPV35 (42%) were also observed. Due to the increased HEs, PEs for HPV16/18/45 and HPV31/33/35 were comparable in the gender-neutral arm 1995 birth cohort. High vaccine efficacy against HPV16/18/45 and, gender-neutral vaccination-enforced, herd effect against HPV18/31/33/35 by the bivalent vaccine rapidly provides comparable overall protective effectiveness against six oncogenic HPV types: 16/18/31/33/35/45.

Human papillomavirus vaccination and the role of herd effects in future cancer control planning: a review

INTRODUCTION

Vaccine herd effects are the indirect protection that vaccinated persons provide to those who remain susceptible to infection, due to the reduced transmission of infections. Herd effects have been an important part of the discourse on how to best implement human papillomavirus (HPV) vaccines and prevent HPV-related diseases.

AREAS COVERED

In this paper, we review the theory of HPV vaccine herd effects derived from mathematical models, give an account of observed HPV vaccine herd effects worldwide, and examine the implications of vaccine herd effects for future cervical cancer screening efforts.

EXPERT COMMENTARY

HPV vaccine herd effects improve the cost-effectiveness of vaccinating preadolescent girls, but contribute to making gender-neutral vaccination less economically efficient. Vaccination coverage and sexual mixing patterns by age are strong determinants of herd effects. Many countries worldwide are starting to observe reductions in HPV-related outcomes likely attributable to herd effects, most notably declining anogenital warts in young men, and declining HPV-16/18 infection prevalence in young unvaccinated women. Policy makers making recommendations for cervical cancer screening will have to consider HPV vaccination coverage and herd effects, as these will affect the positive predictive value of screening and the risk of cervical cancer in unvaccinated women.

Acceptability of a herd immunity-focused, transmission-blocking malaria vaccine in malaria-endemic communities in the Peruvian Amazon: an exploratory study

BACKGROUND

A transmission-blocking vaccine (TBV) to prevent malaria-infected humans from infecting mosquitoes has been increasingly considered as a tool for malaria control and elimination. This study tested the hypothesis that a malaria TBV would be acceptable among residents of a malaria-hypoendemic region.

METHODS

The study was carried out in six Spanish-speaking rural villages in the Department of Loreto in the Peruvian Amazon. These villages comprise a cohort of 430 households associated with the Peru-Brazil International Centre for Excellence in Malaria Research. Individuals from one-third (143) of enrolled households in an ongoing longitudinal, prospective cohort study in 6 communities in Loreto, Peru, were randomly selected to participate by answering a pre-validated questionnaire.

RESULTS

All 143 participants expressed desire for a malaria vaccine in general; only 1 (0.7%) expressed unwillingness to receive a transmission-blocking malaria vaccine. Injection was considered most acceptable for adults (97.2%); for children drops in the mouth were preferred (96.8%). Acceptability waned marginally with the prospect of multiple injections (83.8%) and different projected efficacies at 70 and 50% (90.1 and 71.8%, respectively). Respondents demonstrated clear understanding that the vaccine was for community, rather than personal, protection against malaria infection.

DISCUSSION

In this setting of the Peruvian Amazon, a transmission-blocking malaria vaccine was found to be almost universally acceptable. This study is the first to report that residents of a malaria-endemic region have been queried regarding a malaria vaccine strategy that policy-makers in the industrialized world often dismiss as altruistic.

Knowledge of cervical cancer and HPV vaccine in Bangladeshi women: a population based, cross-sectional study

BACKGROUND

The objective of this study was to assess the level of knowledge of cervical cancer among Bangladeshi women and to assess their willingness to receive the human papillomavirus (HPV) vaccine.

METHODS

A population-based, cross-sectional survey was conducted from July to December 2011 in one urban and one rural area of Bangladesh. A total of 2037 ever-married women, aged 14 to 64 years, were interviewed using a structured questionnaire. Data on socio-demographic characteristics and knowledge of cervical cancer were collected. Willingness to receive the HPV vaccine was assessed. Univariate analyses were completed using quantitative data collected. Multivariable logistic regression models were developed to identify factors associated with having heard of cervical cancer and the HPV vaccine.

RESULTS

The majority of study participants reported to have heard of cervical cancer (urban: 89.7%, rural 93.4%; P = 0.003). The odds of having heard of cervical cancer were significantly higher in urban women aged 35-44 years (aOR: 2.92 (1.34-6.33) and rural women aged 25-34 years (aOR: 2.90 (1.24-6.73) compared to those aged less than 24 years. Very few women reported to have detailed knowledge on risk factors (urban:9.1%, rural: 8.8%) and prevention (urban: 6.4%, rural: 4.4%) of cervical cancer. In our sample, one in five urban women and one in twenty rural women heard about a vaccine that can prevent cervical cancer. Among urban women, secondary education or higher (aOR: 3.48, 95% CI: 1.67-7.25), age of 20 years and above at marriage (aOR: 2.83, 95% CI: 1.61-5.00), and high socioeconomic status (aOR: 2.25, 95% CI: 1.28-3.95) were factors associated with having heard of the HPV vaccine. Willingness to receive the HPV vaccine among study participants either for themselves (urban: 93.9%, rural: 99.4%) or for their daughters (urban: 91.8%, rural: 99.2%) was high.

CONCLUSIONS

Detailed knowledge of cervical cancer among Bangladeshi women was found to be poor. Education on cervical cancer must include information on symptoms, risk factors, and preventive methods. Despite poor knowledge, the study population was willing to receive the HPV vaccine.

Gender-neutrality, herd effect and resilient immune response for sustainable impact of HPV vaccination

PURPOSE OF REVIEW

This review summarize the impact of various strategies of human papillomavirus (HPV) vaccination, such as vaccinating only girls or both girls and boys.

RECENT FINDINGS

Slow and inefficient implementation of HPV vaccination programmes has delayed the impact of the first human cancer vaccine. Vaccinating only girls, with a rather low coverage, has led to a limited herd effect and, thus, not full use of the HPV vaccine potential.

SUMMARY

Gender-neutral vaccination based on comparative effectiveness research will hopefully soon tackle the whole spectrum of HPV cancers in both sexes. The remaining challenges are how to ensure resilience of HPV vaccine-induced immunity and herd effect to guarantee population-level impact of HPV vaccination, and how to guard against HPV type replacement.

The Digital Distribution of Public Health News Surrounding the Human Papillomavirus Vaccination: A Longitudinal Infodemiology Study

Background

New media changes the dissemination of public health information and misinformation. During a guest appearance on the Today Show, US Representative Michele Bachmann claimed that human papillomavirus (HPV) vaccines could cause “mental retardation”.

Objective

The purpose of this study is to explore how new media influences the type of public health information users access, as well as the impact to these platforms after a major controversy. Specifically, this study aims to examine the similarities and differences in the dissemination of news articles related to the HPV vaccination between Google News and Twitter, as well as how the content of news changed after Michele Bachmann’s controversial comment.

Methods

This study used a purposive sampling to draw the first 100 news articles that appeared on Google News and the first 100 articles that appeared on Twitter from August 1-October 31, 2011. Article tone, source, topics, concerns, references, publication date, and interactive features were coded. The intercoder reliability had a total agreement of .90.

Results

Results indicate that 44.0% of the articles (88/200) about the HPV vaccination had a positive tone, 32.5% (65/200) maintained a neutral tone, while 23.5% (47/200) presented a negative tone. Protection against diseases 82.0% (164/200), vaccine eligibility for females 75.5% (151/200), and side effects 59.0% (118/200) were the top three topics covered by these articles. Google News and Twitter articles significantly differed in article tone, source, topics, concerns covered, types of sources referenced in the article, and uses of interactive features. Most notably, topic focus changed from public health information towards political conversation after Bachmann’s comment. Before the comment, the HPV vaccine news talked more often about vaccine dosing (P<.001), duration (P=.005), vaccine eligibility for females (P=.03), and protection against diseases (P=.04) than did the later pieces. After the controversy, the news topic shifted towards politics (P=.01) and talked more about HPV vaccine eligibility for males (P=.01).

Conclusions

This longitudinal infodemiology study suggests that new media influences public health communication, knowledge transaction, and poses potential problems in the amount of misinformation disseminated during public health campaigns. In addition, the study calls for more research to adopt an infodemiology approach to explore relationships between online information supply and public health decisions.

Revising ecological assumptions about Human papillomavirus interactions and type replacement

The controversy over whether vaccine-targeted HPV types will be replaced by other oncogenic, non-vaccine-targeted types remains unresolved. This is in part because little is known about the ecology of HPV types. Patient data has been interpreted to suggest independence or facilitative interactions between types and therefore replacement is believed to be unlikely. With a novel mathematical model, we investigated which HPV type interactions and their immune responses gave qualitatively similar patterns frequently observed in patients. To assess the possibility of type replacement, vaccination was added to see if non-vaccine-targeted types increased their 'niche'. Our model predicts that independence and facilitation are not necessary for the coexistence of types inside hosts, especially given the patchy nature of HPV infection. In fact, independence and facilitation inadequately represented co-infected patients. We found that some form of competition is likely in natural co-infections. Hence, non-vaccine-targeted types that are not cross-reactive with the vaccine could spread to more patches and can increase their viral load in vaccinated hosts. The degree to which this happens will depend on replication and patch colonization rates. Our results suggest that independence between types could be a fallacy, and so without conclusively untangling HPV within-host ecology, type replacement remains theoretically viable. More ecological thinking is needed in future studies.

High HPV-51 prevalence in invasive cervical cancers: results of a pre-immunization survey in North Sardinia, Italy

Background

Human Papilloma virus (HPV) is recognized as the etiological agent of benign and malignant ano-genital lesions. The most prevalent genotypes associated with cervical carcinoma are HPV-16 and -18 worldwide. However, recent studies have emphasized the role of other genotypes, such as HPV-51, in the pathogenesis of cervical dysplasia. The aim of the study was to estimate the burden of HPV-51 infection in invasive cervical malignant lesions in Northern Sardinia, Italy.

Methods/Principal Findings

An observational, retrospective, prevalence, mono-center study was carried out to evaluate the presence of HPV genotypes in tissues biopsies of cervical lesions (CIN-1, CIN-2, CIN-3 and invasive carcinoma) gathered from 1996 to 2009. Biological samples were collected from women admitted consecutively to a tertiary university hospital situated in Sassari, Italy. Molecular methods were used to identify 28 oncogenic HPV types. A total of 155 formalin-fixed and paraffin-embedded cervical tissue samples were analyzed. Approximately half of the cervical lesions were classified as invasive carcinoma. HPV-DNA was detected in 71% of the samples, with a higher frequency (100%) in those categorized as invasive neoplasia. Mono- or co-infections were demonstrated in 45.8% and 25.8% of the cervical samples, respectively. Overall, the most prevalent HPV types were -16 (49%) and -51 (19.4%), with an increased frequency of detection associated with the severity of the cervical lesions.

Conclusions/Significance

This survey highlights for the first time the relevant role of HPV-51 infection in the pathogenesis of invasive cervical cancer prior to the introduction of a vaccination program. Although a selection bias could have influenced the results, other recent studies have described the impact of HPV-51. This remarkable epidemiological element should be carefully evaluated, particularly in the view of opting for preventive vaccines, whose cross-protection patterns determine their efficacy in protecting against infection from HPV types that are not included in the vaccine itself.

Unexpected high prevalence of HPV 90 infection in an underserved population: is it really a low-risk genotype?

CONTEXT

Human papillomavirus 90 (HPV 90) is a rarely reported genotype worldwide, with few data available to characterize its prevalence, distribution, and disease association.

OBJECTIVE

To investigate the prevalence, distribution, and disease association of HPV 90 infection in an underserved inner-city Latino population.

DESIGN

Residual SurePath specimens were collected from 808 women referred for abnormal Papanicolaou tests. DNA microarray against HPV subtypes determined HPV genotypes, followed by confirmatory DNA sequencing assays.

RESULTS

HPV 90 was detected in 32 women (4%) with an average age of 39 years (range, 23-42 years). Most women (31 of 32) had only HPV 90 infection, and one woman was coinfected with HPV 13. Two women had low-grade intraepithelial lesion and one woman had low-grade squamous intraepithelial lesion, cannot exclude high-grade squamous intraepithelial lesion; the rest of the women had negative concurrent cytology. Available concurrent biopsies in 2 of 3 instances with abnormal cytology confirmed HPV cytopathic effect, with no high-risk HPV detected by in situ hybridization.

CONCLUSIONS

We demonstrated an unexpected, high infection rate of HPV 90 in an underserved population in the United States, with 9.4% having concurrent cytologic abnormalities. In the absence of other detectable HPV genotypes by DNA microarray, DNA sequencing, and in situ hybridization, we suspect HPV 90 may be a causative agent responsible for the concurrent cervical lesions. Because of potential shifts in HPV infection patterns in the postvaccine era, monitoring the emergence of previously underrecognized HPV genotypes is becoming increasingly important. To the best of our knowledge, this is the first study to characterize HPV 90 infection in an underserved, North American population.

Prevalence and type distribution of human papillomavirus infection in women from North Sardinia, Italy

Background

Human papillomavirus (HPV) has been associated with several disorders of the genital tract, skin and oropharynx. The aims of our study were to evaluate the prevalence of HPV infection in women between 15 and 54 years of age in North Sardinia, Italy, to identify the prevalence of High Risk - Human papillomaviruses (HR-HPV) genotypes and to establish a correlation between molecular and cytological results.

Methods

From 2007 to 2009 we consecutively enrolled women aged 15-54 years admitted to public and private outpatient settings. All the participants filled in a questionnaire about the socio-cultural state, sexual activity and awareness about HPV. 323 cervical specimens were tested for HPV-DNA and HPV genotypes with INNO-LiPA HPV Genotyping CE Amp kit. Samples showing positivity to some HPV genotypes were re-tested using "in house" quantitative Real-Time PCR assays.

Results

Overall HPV-DNA positivity was detected in 35.9% of the women. The prevalence of HR-HPV infection among HPV positive samples was 93.1% with a specific prevalence of HPV 16, 51, 31, 53 and 18 of 54.3%, 37.9%, 10.3%, 6.9% and 5.2%, respectively. Co-infection with any HPV, HR-HPV, LR-HPV and HR/LR-HPV type was 18.3%, 14.9%, 0.9% and 2.5%, respectively; HPV 16/51 co-infection was detected in 64.6% of the HR-HPV co-infection group. The most frequent HPV-genotypes detected were 16 (32.5%) and 51 (22.7%). Among the 57 patients harboring mono-infection the most prevalent HPV genotypes were 16 (38.6%) and 31(10.5%). A multivariate analysis identified a statistical significant association between HPV infection and age and between HPV infection and previous sexual transmitted diseases. A statistically significant association between cytological cervical lesions and generic HPV exposure was identified.

Conclusions

To our knowledge, this is the first survey evaluating the prevalence of HPV infection in Northern Sardinia and drawing attention to the unusual high proportion of genotype HPV 51. Given the recent implementation of a widespread immunization program with vaccines not containing HPV 51, it has been relevant to prove the high prevalence of this HPV genotype from the start of the vaccination campaign, in order to avoid in the future attributing to the vaccination program a possible selection effect (HPV replacement).

Aspects of prophylactic vaccination against cervical cancer and other human papillomavirus-related cancers in developing countries

Cervical cancer and other human papillomavirus- (HPV-) related cancers are preventable, but preventive measures implemented in developing countries and especially in low-income rural regions have not been effective. Cervical cancer burden derived from sexually transmitted HPV infections is the heaviest in developing countries, and a dramatic increase in the number of cervical cancer cases is predicted, if no intervention is implemented in the near future. HPV vaccines offer an efficient way to prevent related cancers. Recently implemented school-based HPV vaccination demonstration programmes can help tackle the challenges linked with vaccine coverage, and access to vaccination and health services, but prevention strategies need to be modified according to regional characteristics. In urban regions WHO-recommended vaccination strategies might be enough to significantly reduce HPV-related disease burden, but in the rural regions additional vaccination strategies, vaccinating both sexes rather than only females when school attendance is the highest and applying a two-dose regime, need to be considered. From the point of view of both public health and ethics identification of the most effective prevention strategies is pivotal, especially when access to health services is limited. Considering cost-effectiveness versus justice further research on optional vaccination strategies is warranted.

Implementing HPV Vaccines: Public Knowledge, Attitudes, and the Need for Education

This article reviews qualitative research on public knowledge and attitudes to HPV vaccines, focusing on socio-economically challenged populations. Keyword searches were conducted on MEDLINE and ISI Web of Science for relevant peer-reviewed literature in English. A high acceptance of HPV vaccines was found despite low knowledge about HPV (types, prevalence, transmission, health risks, and cervical screening). Facilitators of HPV vaccine uptake included fear of cancer and desire to protect children's health. Barriers included low knowledge levels, perception of HPV vaccines as potential causes of sexual disinhibition, concerns about vaccine costs, social stigma, adverse effects, and parental unwillingness to permit vaccination of pre-adolescent children. Despite acceptance of HPV vaccines, implementation in low-resource settings faces social and economic difficulties. To pursue and strengthen cervical screening in these settings, public education about HPV is key.

A multi-type HPV transmission model

A prophylactic quadrivalent (types 6/11/16/18) vaccine against oncogenic and warts-causing genital Human papillomavirus (HPV) types was approved by the US Food and Drug Administration in 2006. This paper presents a nonlinear, deterministic, age-structured, mathematical model of the transmission dynamics of HPV and disease occurrence in a US population stratified by gender and sexual activity group. The model can assess both the epidemiologic consequences and cost effectiveness of alternative vaccination strategies in a setting of organized cervical cancer screening in the United States. Inputs for the model were obtained from public data sources, published literature, and analyses of clinical trial data. The results suggest that a prophylactic quadrivalent HPV vaccine can: (i) substantially reduce the incidence of disease, (ii) increase survival among females, (iii) improve quality of life for both males and females, (iv) be cost-effective when administered to females age 12-24 years, and (v) be cost-effective when implemented as a strategy that combines vaccination of both females and males before age 12 vaccination with a 12 to 24 years of age catch-up vaccination program.

Chapter 18: Public health policy for cervical cancer prevention: the role of decision science, economic evaluation, and mathematical modeling

Several factors are changing the landscape of cervical cancer control, including a better understanding of the natural history of human papillomavirus (HPV), reliable assays for detecting high-risk HPV infections, and a soon to be available HPV-16/18 vaccine. There are important differences in the relevant policy questions for different settings. By synthesizing and integrating the best available data, the use of modeling in a decision analytic framework can identify those factors most likely to influence outcomes, can guide the design of future clinical studies and operational research, can provide insight into the cost-effectiveness of different strategies, and can assist in early decision-making when considered with criteria such as equity, public preferences, and political and cultural constraints.

Parental acceptance of Human Papillomavirus vaccines

OBJECTIVE

To determine whether parents would accept Human Papillomavirus (HPV) vaccination for their children and which variables may influence their decision, including knowledge about cervical cancer and HPV.

STUDY DESIGN

Three hundred and fifty-six parents of children aged 10-12 years were interviewed regarding the acceptance of an HPV vaccine for their children and their knowledge of HPV and cervical cancer. All data were recorded anonymously. Results were compared using the chi(2)- and the Mann-Whitney test.

RESULTS

HPV vaccination would be accepted by 88% of the parents, preferably when the child is aged 10-12 years. Parents of children who received all the vaccinations of the National Vaccination Programme accepted HPV vaccination significantly more. Less than a third of all parents had heard of HPV, and 14% were aware of the causal relationship of HPV and cervical cancer. Knowledge of HPV and cervical cancer, religion, age, education, and marital status did not show any significant relation with HPV vaccine acceptance.

CONCLUSIONS

A majority of the parents would accept HPV vaccination. HPV vaccine acceptance seems to be dependent on vaccine acceptance in general, even more than on knowledge of HPV and its causal relation with cervical cancer. However, parents requested more information about cervical cancer, HPV, and HPV vaccination, before the HPV vaccine is introduced.

Human papillomavirus prevalence and predictors for cervical cancer among high-risk women from Rio de Janeiro, Brazil

We assess the prevalence of human papillomavirus (HPV) and cofactors for cervical severe disease, as contribution for vaccine strategies at the right moment in which Brazilian health authorities have approved an anti-HPV vaccine. A case-control study was undertaken with 201 women who attended a public health service with previous abnormal cytology. The HPV status was ascertained by consensus primers My09/11 and typed by 6, 11, 16, 18, 31, 33, 35, and 58 specific primers. Patients diagnosed with high-grade squamous intraepithelial lesions (HSIL) and cervical cancer were referred as cases (n = 84). Patients with normal/inflammatory cervix or carrying benign cervical lesions were included in controls (n = 117). The overall prevalence of HPV infection was 75.6%, with 91.7% among cases. In spite of HPV 16 being the most frequent type (53.3%), 27.6% of infections were attributed to nonvaccine types. High-risk HPV were strongly associated to older women (OR = 6.7). Otherwise, age at the first intercourse (OR = 7.10), three or more parities (OR = 3.05), abortion episodes (OR = 4.80), and smoking (OR = 3.83) conferred a heavy effect in younger women. Among mediators affecting the progress from HSIL to cancer, age played the main role in easing the progression (OR = 1.09, P = 0.002) followed by education level (OR = 4.20, P = 0.066). White ethnia showed to be a protective factor (OR = 0.32, P = 0.055). Predictors from HPV exposure to malignant disease include demographic and behavioral factors. Public policies such as improvement of education and continued prevention campaigns might contribute to reduce this picture. This work also gives background, in identifying a target population, for implementing future vaccine strategies.

A public health approach to cervical cancer control: considerations of screening and vaccination strategies

Cervical cancer remains a leading cause of cancer death among women living in low-resource settings. In the last 3 decades, cytologic screening has -in theory -been available and yet more than 6 million women have died of this preventable disease. The necessary resources, infrastructure, and technological expertise, together with the need for repeated screenings at regular intervals, make cytologic screening difficult to implement in poor countries. As noncytologic approaches for the detection of HPV, simple visual screening methods for anogenital lesions caused by HPV, and the availability of an HPV-16/18 vaccine will enhance the linkage between screening and treatment, multiple factors will need to be considered when designing new, or modifying existing prevention strategies. Countryspecific decisions regarding the best strategy for cervical cancer control will need to rely on data from many sources and take into account complex epidemiologic, economic, social, political, and cultural factors, and be made despite uncertainty and incomplete information. A rigorous decision analytic approach using computerbased modeling methods enables linkage of the knowledge gained from empirical studies to real-world situations. This chapter provides an introduction to these methods, reviews lessons learned from cost-effectiveness analyses of cervical cancer screening in developed and developing countries, and emphasizes important qualitative themes to consider in designing cervical cancer prevention policies.

[Prevention of cervical cancer (II): prophylactic HPV vaccination, current knowledge, practical procedures and new issues]

Despite the considerable success of early screening for prevention of cervical cancer, Pap smears have not fulfilled the hopes that it would lead to a large-scale reduction of this cancer's incidence. Screening appears to be useful for a tiny portion of the world population, although a relatively large portion must put up with its limitations and disadvantages. Human papilloma viruses (HPV) 16 and 18 are responsible for two thirds of all cervical cancers worldwide. The condylomata (condyloma acuminatum), or genital warts, induced by HPV 6 and 11 are frequent among the young and difficult to manage. The extent and burden of HPV infection are considerable, as is the psychological and emotional impact of the diseases associated with it. Because cancer of the cervix is the final consequence of chronic HPV infection, it can be prevented by vaccination. A prophylactic vaccine to protect against the precancerous and cancerous lesions associated with HPV should save lives, reduce expensive diagnostic and therapeutic interventions, and have substantial individual and collective benefits. Clinical trials of anti-HPV vaccines for the prevention of cervical cancer and condyloma have shown remarkable results and an efficacy unequaled in the history of vaccination against infectious diseases. Vaccine efficacy has been shown only in young girls never exposed to the virus and only for the lesions associated with the specific viral types in the vaccine. Preliminary data indicate that the vaccination is effective in women who have previously eliminated naturally the virus. It has no therapeutic effects on existing lesions or in healthy virus carriers. Practical questions remain to be resolved. If the vaccination is left to individual initiative and vaccination coverage is insufficient, there will be no perceptible reduction in the frequency of cervical cancer. Vaccination policies will not be identical in poor countries, where the disease represents one of the leading causes of mortality among women, and in the rich countries, where screening programs have considerably reduced the frequency of this cancer. Current planning calls for the introduction of systematic vaccination of young girls aged 9-15 years, with progressive "catch-up" vaccination of the cohorts of young women aged 16-26 years. Nonetheless mathematical models and immunogenicity results indicate a possible benefit for individual vaccination of adults. This approach must still be assessed in the clinical trials underway. Because the vaccine does not protect against all types of HPV associated with cervical cancer, screening must be continued according to the conditions currently set. Vaccination and screening, which are complementary and synergistic, now constitute the new standards for prevention of this disease.

How will HPV vaccines affect cervical cancer?

Cancer of the uterine cervix is the second largest cause of cancer deaths in women, and its toll is greatest in populations that lack screening programmes to detect precursor lesions. Persistent infection with 'high risk' genotypes of human papillomavirus (HPV) is necessary, although not sufficient, to cause cervical carcinoma. Therefore, HPV vaccination provides an opportunity to profoundly affect cervical cancer incidence worldwide. A recently licensed HPV subunit vaccine protects women from a high proportion of precursor lesions of cervical carcinoma and most genital warts. Here we examine the ramifications and remaining questions that surround preventive HPV vaccines.

Mathematical model of HPV provides insight into impacts of risk factors and vaccine

Kim discusses a study by Barnabas and colleagues in PLoS Medicine in which the researchers used a mathematical model to assess the effect of sexual transmission of HPV 16 in a Finnish population.

Prévention du cancer du col utérin : enjeux et perspectives de la vaccination antipapillomavirus

Cervical cancer remains a critical public health problem that is second only to breast cancer in overall disease burden for women throughout the world. In spite of the success of cervical cancer screening, Pap cytology screening is yet to be effectively implemented or has failed to reduce cervical cancer rates to an appreciable extent. Screening appears to benefit only a small fraction of women although a much larger percentage endures the inconvenience of the Pap test in order to avoid cervical cancer. The establishment of Human Papillomavirus (HPV) infection as the necessary cause of cervical precancers and cancers provides a tremendous opportunity for cervical cancer prevention through vaccination. HPV 16 and 18 which cause 70% of cervical cancers worldwide. Thus a prophylactic vaccine to prevent HPV related precancerous lesions and cancers would save lives, reduce the need for costly medical procedures and provide both women and communities throughout the world with substantial benefits. Based on the induction of neutralizing antibodies by non infectious Virus Like Particles (VLP) of L1 capside protein, prophylactic HPV vaccines have consistently induced high titter of neutralizing antibodies with minimal side effects and induce more than 90% protection from persistent HPV 16-18 infection and HPV 16 and 18 associated high-grade Cervical Intraepithelial Neoplasia (CIN) in proof of concept efficacy trials. HPV 16-18 vaccination will prevent HPV16-18 incident infection, and subsequently decrease in 90% the frequency of abnormal Pap attributable to these types and in about 50% overall abnormal Pap. HPV vaccination will reduce the number of women who require colposcopy, biopsy and cervical treatment for precancerous cervical lesions. The level of protection from death due to cervical cancer could exceed 95%. Three large phases prophylactic HPV VLP trials are now in progress and will form the basis for licensing of candidate vaccines in 2006. HPV vaccination targeting young female adolescents, aged 11 to 16 years, with a catch-up of those aged 17-25 years, would be a strategy to be addressed. Cervical cancer screening strategies, that will be cost-effective for the proper surveillance of women protected by HPV vaccination, are under analysis.

Vaccines for cervical cancer

The review focuses on current and future prevention of invasive cervical cancer (ICC), the second most common cancer among women worldwide. Implementation of population-based cytological screening programmes, using the 'Pap' smear to detect pre-cancerous lesions in the cervix, has resulted in substantial declines in mortality and morbidity from ICC in North America and some European countries. However, cases of, and deaths from, ICC continue to occur. Primary prevention of infection with high-risk human papillomavirus (HPV) types, the central causal factor of ICC, could further reduce incidence of and mortality from ICC. This is particularly the case in developing countries, which bear 80% of the burden of ICC, and where effective Pap screening programmes are extremely difficult to implement. Very promising results from several trials of synthetic HPV type-specific monovalent (HPV 16) and bivalent (HPV 16 and 18) vaccines have recently been published, showing high efficacy against type-specific persistent HPV infection and development of type-specific pre-cancerous lesions. Large-scale phase III trials of a number of such vaccine candidates are currently underway, and there is real hope that an effective vaccine capable of protecting against infection with HPV types 16 and 18 (which together account for approximately 70% of cervical cancer cases worldwide), and thereby of preventing development of a very significant proportion of cases of ICC, could be available within the next 2 years.

Vaccination against multiple HPV types

Vaccines against the most common human papillomavirus (HPV) types are currently under development. Epidemiologic data suggest that the transmission dynamics of different HPV types are not independent. Some studies indicate that interactions among HPV types are synergistic, where infection with one type facilitates concurrent or subsequent infection with another HPV type. Other studies point to antagonistic interference among HPV types. Here we develop a mathematical model to explore how these interactions may either enhance or diminish the effectiveness of vaccination programs designed to reduce the prevalence of the HPV types associated with cervical cancer. We analyze the local stability of the infection-free and boundary equilibria and characterize the conditions leading to a coexistence equilibrium. We also illustrate the results with numerical simulations using realistic model parameters. We show that if interactions among HPV types are synergistic, mass vaccination may reduce the prevalence of types that are not even included in the vaccine.

First-generation vaccines against human papillomavirus

There has been considerable progress in the development of a prophylactic human papillomavirus vaccine in the past 10 years, since the discovery of human papillomavirus virus-like particles. Licensure of the human papillomavirus vaccine is probably not far away. This would make it the first licensed vaccine against a common sexually transmitted infection. Although hepatitis B is a sexually transmitted infection for which there is an effective prophylactic vaccine, it is often not perceived as such by individuals taking the vaccine. Preclinical studies have already produced attractive vaccine candidates and recent clinical trials have yielded strikingly promising results. The candidate vaccines are generally well tolerated, induce high titers of serum antibodies to the human papillomavirus types and effectively prevent acquisition of infection and early clinical disease caused by common human papillomavirus types.

Human papillomavirus infection: biology, epidemiology, and prevention

Over the past several decades, knowledge of the biology and epidemiology of human papillomavirus (HPV) infection has increased tremendously. However, there are still many unanswered questions concerning the interaction of the virus with its host. The virus has been identified as a necessary causal agent for cervical squamous neoplasia and has been linked to the development of neoplasia in several other mucosal sites. The viral oncogenes E6 and E7 are the major players in the virus' scheme to evade the immune system and use the host cell replication machinery to survive. Many risk factors for infection with HPV have been identified; however, the focus now centers on identifying risk factors for persistence of the infection as it is likely that transient infections play a very small role in the overall development of clinical disease. Prevention measures to date have centered around screening programs, mostly for cervical cancer, including the perfection of screening techniques and inclusion of molecular testing for HPV into screening regimens. The development of prophylactic and therapeutic vaccines has also increased as primary prevention measures appear to have the best hope for long-term effects on cancer incidence.

Role of Herd Immunity in Determining the Effect of Vaccines against Sexually Transmitted Disease

BACKGROUND

Vaccination programs provide both direct protection to those immunized and herd immunity, which is indirect protection of those who remain susceptible, owing to a reduced prevalence of infections.

METHODS

The well-understood impact of vaccination against ubiquitous childhood infections is compared with that of vaccination against sexually transmitted infections (STIs), and theoretical insights are derived from a review of mathematical modeling studies.

RESULTS

Typically, a large fraction of cases of STIs are acquired by those with modest risk, and these cases could be prevented by low-efficacy vaccines. If coverage is good, vaccination of only one sex can protect the other sex. Candidate vaccines against human papillomavirus (HPV) and genital herpes are in the final stages of testing. The former is likely to be highly efficacious for a limited number of disease-causing HPV types, and the latter has provided protection against disease in women who initially were seronegative for both herpes simplex virus (HSV) type 1 and HSV-2, with 73% efficacy. In models, this vaccine had a substantial impact when infectiousness was assumed to be reduced along with incidence of disease.

CONCLUSION

With such vaccines on the horizon, the requirements for vaccine delivery need to be considered, particularly who should be vaccinated and at what age.

Evaluating human papillomavirus vaccination programs

Human papillomavirus (HPV) has been implicated as the primary etiologic agent of cervical cancer. Potential vaccines against high-risk HPV types are in clinical trials. We evaluated vaccination programs with a vaccine against HPV-16 and HPV-18. We developed disease transmission models that estimated HPV prevalence and infection rates for the population overall, by age group, by level of sexual activity within each age group, and by sex. Data were based on clinical trials and published and unpublished sources. An HPV-16/18 vaccine for 12-year-old girls would reduce cohort cervical cancer cases by 61.8%, with a cost-effectiveness ratio of 14,583 dollars per quality-adjusted life year (QALY). Including male participants in a vaccine rollout would further reduce cervical cancer cases by 2.2% at an incremental cost-effectiveness ratio of 442,039 dollars/QALY compared to female-only vaccination. Vaccination against HPV-16 and HPV-18 can be cost-effective, although including male participants in a vaccination program is generally not cost-effective, compared to female-only vaccination.

Projected Clinical Benefits and Cost-effectiveness of a Human Papillomavirus 16/18 Vaccine

BACKGROUND

Human papillomavirus (HPV) vaccine may be commercially available in a few years. We explored the clinical benefits and cost-effectiveness of introducing an HPV16/18 vaccine in a population with an organized cervical cancer screening program.

METHODS

A computer-based model of the natural history of HPV and cervical cancer was used to project cancer incidence and mortality, life expectancy (adjusted and unadjusted for quality of life), lifetime costs, and incremental cost-effectiveness ratios (i.e., the additional cost of a strategy divided by its additional clinical benefit compared with the next most expensive strategy) associated with different cancer prevention policies, including vaccination (initiated at age 12 years), cytologic screening (initiated at 18, 21, 25, 30, or 35 years), and combined vaccination and screening strategies. We assumed that vaccination was 90% effective in reducing the risk of persistent HPV16/18 infections and evaluated alternative assumptions about vaccine efficacy, waning immunity, and risk of replacement with non-16/18 HPV types.

RESULTS

Our model showed that the most effective strategy with an incremental cost-effectiveness ratio of less than 60 dollars-000 per quality-adjusted life year is one combining vaccination at age 12 years with triennial conventional cytologic screening beginning at age 25 years, compared with the next best strategy of vaccination and cytologic screening every 5 years beginning at age 21 years. This triennial strategy would reduce the absolute lifetime risk of cervical cancer by 94% compared with no intervention. These results were sensitive to alternative assumptions about the underlying patterns of cervical cancer screening, duration of vaccine efficacy, and natural history of HPV infection in older women.

CONCLUSIONS

Our model predicts that a vaccine that prevents persistent HPV16/18 infection will reduce the incidence of HPV16/18-associated cervical cancer, even in a setting of cytologic screening. A program of vaccination that permits a later age of screening initiation and a less frequent screening interval is likely to be a cost-effective use of health care resources.

Chapter 16: Prophylactic human papillomavirus vaccines

Candidate prophylactic vaccines based on papillomavirus L1 virus-like particles (VLPs) are currently in human clinical trials. The main long-term goal of the vaccine is to reduce the incidence of cervical cancer and its precursors. In animal papillomavirus models, systemic immunization with L1 VLPs can induce high titers of neutralizing antibodies that confer protection against high-dose experimental papillomavirus challenge. In humans, systemic vaccination with L1 VLPs has been well tolerated and induced high serum antibody titers (at least 40 times higher than titers seen following natural infection). A recent proof of principle HPV16 L1 VLP efficacy trial has shown excellent protection against persistent HPV16 infection and associated cytological abnormalities. Large scale efficacy trials of L1 VLPs from HPV16 and 18 (the HPV types found most frequently in cervical cancer), with or without HPV6 and 11 (the HPV types responsible for most genital warts), are planned. If the results of these large trials support the encouraging results of the early trials, they should lead to a commercial prophylactic HPV vaccine. Implementation issues may include how to make the vaccine available in the developing world, where the majority of cervical cancer cases occur, the appropriate age of vaccination, and the role of male vaccination. Because a VLP vaccine is likely to provide type-specific protection, increasing the number of cancer-associated HPV types in the vaccine is a likely approach to broadening the protection to additional types. There will probably also be efforts to develop alternative vaccine formulations better suited to implementation in developing countries as well as attempts to develop vaccines with a therapeutic activity against established HPV infection because a combined prophylactic/therapeutic vaccine may be expected to have an even greater impact than a purely prophylactic vaccine on HPV induced disease.

Primary prevention of uterine cervix cancer: focus on vaccine history and current strategy

Primary prevention of uterine cervix cancer spans the gamut of human papillomavirus vaccine development, dietary adjustment, chemoprevention, and risk reduction. Lifestyle and social behaviors impact on risk for cervical cancer. Before examining the growing body of molecular evidence, animal studies, and phase I clinical trials that suggest that a virus-based vaccine for cervical cancer may soon become a reality, one must reflect on what has gone before in the vaccine-based battle with viral disease.

The theoretical population-level impact of a prophylactic human papilloma virus vaccine

BACKGROUND

The ongoing development of a vaccine against human papillomavirus (HPV) raises important questions about the impact of various vaccination strategies.

METHODS

Two mathematical models are developed to explore the population-level impact of an HPV vaccine. The first model focuses on the infection process and the second on the disease process (specifically, cervical carcinoma and cancer).

RESULTS

Both population characteristics (, sexual mixing and rates of sex partner change) and vaccine characteristics affect the steady state prevalence of HPV that would be expected if a vaccine program is implemented. Under a particular set of assumptions, we find that vaccinating both men and women against a specific HPV type would result in a 44% decrease in prevalence of that type whereas vaccinating only women would result in a 30% reduction. We also find that if a vaccine gives protection against some, but not all, high risk types of HPV, the reduction in disease may be less than the reduction in HPV because the remaining high risk HPV types may replace the disease caused by the eliminated types.

CONCLUSIONS

A multivalent vaccine containing the majority of disease-causing HPV types would greatly reduce the need for colposcopy, biopsy and treatment. However, it is unlikely that Pap-screening programs would become redundant unless the vaccine is highly effective and coverage is widespread. In contrast to less common infections that are primarily restricted to core groups, targeting the vaccine towards the most sexually active individuals is less effective for a common sexually transmitted infection such as HPV.

The use of vaccines in the prevention and treatment of cervical cancer

The close association between high risk HPV infection and cervical carcinoma has provided the impetus for the development of prophylactic and therapeutic vaccination schedules. An effective prophylactic vaccine would obviate the need for population-based cervical screening programmes, while therapeutic vaccination might provide an effective adjunct to or replacement for conventional treatment for benign and malignant cervical disease. While the challenges associated with the design and implemention of immunotherapies are numerous, optimism remains high and it is expected that the next few decades will witness a revolutionary change in the way we treat cervical cancer and its premalignant lesions. A papillomavirus vaccine that prevented HPV infection on the one hand and acted against established disease on the other, would have a profound impact on one of the major cancers affecting women globally.

The role of human papillomavirus vaccines in cervical neoplasia

Cervical cancer is the second most common cause of cancer-related death in women, in some developing countries accounting for the highest cancer mortality. The evidence for the association of high-risk human papillomavirus types with the aetiology of cervical neoplasia is firmly established, human papillomavirus being detected in virtually all cervical cancers. The risk of progression of precursor cervical intra-epithelial neoplasia lesions is associated with persistence of human papillomavirus infection. One strategy for the management of cervical neoplasia worldwide could be the development of prophylactic and/or therapeutic human papillomavirus vaccines. This chapter will discuss the natural history of human papillomavirus infection, viral immunity and the clinical course of resultant disease as the background to the effective design and use of human papillomavirus vaccines for protection or therapy. The progress of ongoing phase I and II clinical trials for several different vaccine preparations and the challenges for establishing their future use will be discussed.

Prospects for phase III-IV HPV vaccination trials in the Nordic countries and in Estonia

BACKGROUND

oncogenic, i.e. high risk human papillomavirus (hrHPV) types are the major cause of invasive cervical cancer (ICC). Putatively licensable vaccines against the hrHPVs have been developed and are approaching clinical phase III trials that use persistent HPV infection as end point. Direct extension of the phase III trials towards long-term end points (ICC and its immediate precursors: carcinoma in situ and severe dysplasia, i.e. cervical intraepithelial neoplasia grade III, CINIII) is important, to avoid early contamination of the target population by opportunistic use of licensed HPV vaccines. Country-wide registration on population and health events in a stable population of 25 million make Estonia and the Nordic countries a unique venue for long-term evaluation of cervical cancer control measures. Mass-screening programmes exist in all Nordic countries, but not in Estonia.

AIM

design of phase III-IV trials for evaluation of protection against ICC and CINIII by preventive HPV vaccines based on cancer registry follow-up.

RESULTS

in the Nordic countries, population based randomisation of all 15-year-old women to the vaccination (vaccine and placebo) and reference cohorts entering conventional Pap-smear screening after a clinical phase III trial would assure comparability of the cohorts. Enrollment of 10094 vaccinees +10094 placebo vaccinees +30282 other hrHPV negative women without vaccination at the age of 16 would give 80% power for the demonstration of 70% vaccine efficacy (VE) against ICC in 20 years by cancer registry follow-up. On the other hand, vaccination of 8303 Estonian hrHPV negative women among the entire 15-year-old female birth cohort (about 10000 women) with an already licensed HPV vaccine would enable demonstration of 70% VE against ICC by 20 years of registry follow-up of these and comparable 16606 women identified among the 16-19-year-old birth cohorts.

CONCLUSIONS

evaluation of the protective effect of an HPV vaccine against ICC is possible both in countries with or without mass-screening. The effects of vaccination on spread of different HPVs in the population would need to be monitored, especially in Estonia. Ethical aspects, cost-benefit evaluation and comparisons with other new means of cervical cancer control warrant further investigation.