Benefits of catch-up in vaccination against human papillomavirus in medium- and low-income countries

Present challenges in cervical cancer prevention: Answers from cost-effectiveness analyses

Simulation models are commonly used to address important health policy issues that cannot be explored through experimental studies. These models are especially useful to determine a set of strategies that result in a good value for money (cost-effectiveness). Several mathematical models simulating the natural history of HPV and related diseases, especially cervical cancer, have been developed to calculate a relative effectiveness and cost-effectiveness of HPV vaccination and cervical cancer screening interventions. Virtually all cost-effectiveness analyses identify HPV vaccination programmes for preadolescent girls to be cost-effective, even for relatively low vaccination coverage rates. Routine vaccination of preadolescent girls is the primary target population for HPV vaccination as it shows to provide the greatest health impact. Cost-effectiveness analyses assessing other vaccine target groups are less conclusive. Adding additional age-cohorts would accelerate health benefits in some years, although cost-effectiveness becomes less favourable as age at vaccination increases. Including men in HPV vaccination programmes may be a less efficient strategy if done at the expense of female vaccination coverage for reducing the burden of HPV in the population. However, as the HPV vaccine price decreases, the cost-effectiveness of universal vaccination improves, becoming equally as efficient as female-only vaccination. Vaccine price is a decisive factor in the cost-effectiveness analyses. The lower the price, the greater the likelihood that vaccination groups other than the primary target would be considered cost-effective.

Options for design of real-world impact studies of single-dose vaccine schedules

Based on existing evidence for efficacy, savings, and advantages in delivery, some countries may elect to pilot or roll out single-dose human papillomavirus (HPV) vaccination (instead of, or in combination with, two-dose) in advance of a WHO policy decision. Accelerated evidence of population-based effectiveness (hereafter referred to as overall effectiveness, OE) of one-dose vaccine programs could be gained through regular surveys of HPV prevalence in young women before and after vaccination introduction. In order to offer the earliest information on OE, one-dose HPV vaccination should target one or more birth cohorts as close as possible to the age when sexual activity most often starts in a given population. A catch-up one-dose vaccination program of girls up to 18 years of age who would have been too old to profit from the introduction of a routine HPV vaccination program in preadolescents would minimize the interval between vaccination and the possibility to monitor vaccination impact in young women. In addition, catch-up is especially desirable in low- and middle-income countries with little access to screening as "missed" cohorts may face high risk of cervical cancer death. HPV prevalence should be firstly monitored in age groups of women who may already be sexually active but still reluctant to admit it and to accept vaginal examination for the collection of cervical cells. Hence, HPV testing from urine samples, for which good concordance with cervical cells has been proven, offers a feasible approach to assess periodically vaccine OE in representative samples of 17-20 year-old women. This type of observational study would greatly benefit from the presence of a population census and the creation of a vaccination registry. A real-world demonstration of OE of the new schedule would complement the findings of ongoing clinical trials and immunogenicity studies on the efficacy of single-dose HPV vaccination.

Potential lives saved in 73 countries by adopting multi-cohort vaccination of 9-14-year-old girls against human papillomavirus

Up to 2016, low- and middle-income countries mostly introduced routine human papillomavirus (HPV) vaccination for just a single age-cohort of girls each year. However, high-income countries have reported large reductions in HPV prevalence following "catch-up" vaccination of multiple age-cohorts in the year of HPV vaccine introduction. We used the mathematical model PRIME to project the incremental impact of vaccinating 10- to 14-year-old girls compared to routine HPV vaccination only in the same year that routine vaccination is expected to be introduced for 9-year-old girls across 73 low- and lower-middle-income countries. Adding multiple age-cohort vaccination could increase the number of cervical cancer deaths averted by vaccine introductions in 2015-2030 by 30-40% or an additional 1.23-1.79 million over the lifetime of the vaccinated cohorts. The number of girls needed to vaccinate to prevent one death is 101 in the most pessimistic scenario, which is only slightly greater than that for routine vaccination of 9-year-old girls (87). These results hold even when assuming that girls who have sexually debuted do not benefit from vaccination. Results suggest that multiple age-cohort vaccination of 9- to 14-year-old girls could accelerate HPV vaccine impact and be cost-effective.

Age of Acquiring Causal Human Papillomavirus (HPV) Infections: Leveraging Simulation Models to Explore the Natural History of HPV-induced Cervical Cancer

Background

Although new human papillomavirus (HPV) infections can occur at all ages, the age at which women acquire their "causal" HPV infection that develops into cervical cancer is poorly understood and practically unobservable. We aimed to estimate the age distribution at which individuals acquired their causal HPV infection in the absence of HPV vaccination or screening to help guide the optimal use of both.

Methods

Using an empirically calibrated mathematical model that simulates the natural history of cervical cancer, we estimated the cumulative number of causal HPV infections by age, stratified by HPV genotype (HPV16 vs. other HPV genotypes), and the direct age-specific reduction in cancer incidence for alternative vaccination initiation scenarios (i.e., age 9-45 years).

Results

Our model projected that among all cervical cancers, 50% and 75% of women acquired their causal HPV infection by ages 20.6 (range: 20.1-21.1) and 30.6 (range: 29.6-31.6) years, respectively. HPV16 infections were acquired at an earlier age. Assuming 95% efficacy against HPV16 and HPV18 infections, the direct reduction in lifetime risk of cervical cancer varied from 55% (53-56%) among women vaccinated at age 9 years to 6% (range: 6-7%) among women vaccinated at age 45 years. Similar patterns were observed for the second-generation vaccine.

Conclusions

Although new HPV infections and precancers can occur throughout a woman's lifetime, only a small proportion are acquired in mid-adult women and are vaccine-preventable. Our simulations highlight the potential limitations of using surrogate endpoints for vaccine efficacy studies of mid-adult women to guide policy decisions for implementation.

Cervical cancer prevention and treatment research in Africa: a systematic review from a public health perspective

BACKGROUND

Women living in Africa experience the highest burden of cervical cancer. Research and investment to improve vaccination, screening, and treatment efforts are critically needed. We systematically reviewed and characterized recent research within a broader public health framework to organize and assess the range of cervical cancer research in Africa.

METHODS

We searched online databases and the Internet for published articles and cervical cancer reports in African countries. Inclusion criteria included publication between 2004 and 2014, cervical cancer-related content pertinent to one of the four public health categories (primary, secondary, tertiary prevention or quality of life), and conducted in or specifically relevant to countries or regions within the African continent. The study design, geographic region/country, focus of research, and key findings were documented for each eligible article and summarized to illustrate the weight and research coverage in each area. Publications with more than one focus (e.g. secondary and tertiary prevention) were categorized by the primary emphasis of the paper. Research specific to HIV-infected women or focused on feasibility issues was delineated within each of the four public health categories.

RESULTS

A total of 380 research articles/reports were included. The majority (54.6 %) of cervical cancer research in Africa focused on secondary prevention (i.e., screening). The number of publication focusing on primary prevention (23.4 %), particularly HPV vaccination, increased significantly in the past decade. Research regarding the treatment of precancerous lesions and invasive cervical cancer is emerging (17.6 %), but infrastructure and feasibility challenges in many countries have impeded efforts to provide and evaluate treatment. Studies assessing aspects of quality of life among women living with cervical cancer are severely limited (4.1 %). Across all categories, 11.3 % of publications focused on cervical cancer among HIV-infected women, while 17.1 % focused on aspects of feasibility for cervical cancer control efforts.

CONCLUSIONS

Cervical cancer research in African countries has increased steadily over the past decade, but more is needed. Tertiary prevention (i.e. treatment of disease with effective medicine) and quality of life of cervical cancer survivors are two severely under-researched areas. Similarly, there are several countries in Africa with little to no research ever conducted on cervical cancer.

HPV-FASTER: broadening the scope for prevention of HPV-related cancer

Human papillomavirus (HPV)-related screening technologies and HPV vaccination offer enormous potential for cancer prevention, notably prevention of cervical cancer. The effectiveness of these approaches is, however, suboptimal owing to limited implementation of screening programmes and restricted indications for HPV vaccination. Trials of HPV vaccination in women aged up to 55 years have shown almost 90% protection from cervical precancer caused by HPV16/18 among HPV16/18-DNA-negative women. We propose extending routine vaccination programmes to women of up to 30 years of age (and to the 45-50-year age groups in some settings), paired with at least one HPV-screening test at age 30 years or older. Expanding the indications for HPV vaccination and much greater use of HPV testing in screening programmes has the potential to accelerate the decline in cervical cancer incidence. Such a combined protocol would represent an attractive approach for many health-care systems, in particular, countries in Central and Eastern Europe, Latin America, Asia, and some more-developed parts of Africa. The role of vaccination in women aged >30 years and the optimal number of HPV-screening tests required in vaccinated women remain important research issues. Cost-effectiveness models will help determine the optimal combination of HPV vaccination and screening in public health programmes, and to estimate the effects of such approaches in different populations.

HPV vaccination: The most pragmatic cervical cancer primary prevention strategy

The evidence that high-risk HPV infections cause cervical cancers has led to two new approaches for cervical cancer control: vaccination to prevent HPV infections, and HPV screening to detect and treat cervical precancerous lesions. Two vaccines are currently available: quadrivalent vaccine targeting oncogenic HPV types 16, 18, 6, and 11, and bivalent vaccine targeting HPV 16 and 18. Both vaccines have demonstrated remarkable immunogenicity and substantial protection against persistent infection and high-grade cervical cancer precursors caused by HPV 16 and 18 in HPV-naïve women, and have the potential to prevent 70% of cervical cancers in adequately vaccinated populations. HPV vaccination is now implemented in national programs in 62 countries, including some low- and middle-income countries. The early findings from routine national programs in high-income countries are instructive to encourage low- and middle-income countries with a high risk of cervical cancer to roll out HPV vaccination programs and to introduce resource-appropriate cervical screening programs.

Introduction of a National HPV vaccination program into Bhutan

BACKGROUND

Cervical cancer is the most common cancer in Bhutanese women. To help prevent the disease, the Ministry of Health (MoH) developed a national human papillomavirus (HPV) vaccine program.

METHODS

MoH considerations included disease incidence, the limited reach of cervical screening, poor outcomes associated with late diagnosis of the disease, and Bhutan's ability to conduct the program. For national introduction, it was decided to implement routine immunization for 12 year-old girls with the quadrivalent HPV6/11/16/18 (QHPV) vaccine and a one-time catch-up campaign for 13-18 year-old girls in the first year of the program (2010). Health workers would administer the vaccine in schools, with out-of-school girls to receive the vaccine at health facilities. From 2011, HPV vaccination would enter into the routine immunization schedule using health-center delivery.

RESULTS

During the initial campaign in 2010, over 130,000 doses of QHPV were administered and QHPV 3-dose vaccination coverage was estimated to be around 99% among 12 year-olds and 89% among 13-18 year-olds. QHPV vaccine was well tolerated and no severe adverse events were reported. In the three following years, QHPV vaccine was administered routinely to 12 year-olds primarily through health centers instead of schools, during which time the population-level 3-dose coverage decreased to 67-69%, an estimate which was confirmed by individual-level survey data in 2012 (73%). In 2014, when HPV delivery was switched back to schools, 3-dose coverage rose again above 90%.

DISCUSSION

The rapid implementation and high coverage of the national HPV vaccine program in Bhutan were largely attributable to the strength of political commitment, primary healthcare and support from the education system. School-based delivery appeared clearly superior to health centers in achieving high-coverage among 12 year-olds.

CONCLUSIONS

Bhutan's lessons for other low/middle-income countries include the superiority of school-based vaccination and the feasibility of a broad catch-up campaign in the first year.

The next steps in cervical screening

Cervical cancer is fourth most common cancer among women with four-fifths of the global burden in low- and middle-income countries (LMICs). Persistent infection with one of the high-risk types of human papillomaviruses (HPV), particularly HPV 16/18, is the central cause of cervical neoplasia. Progress in developing feasible, alternative screening methods in LMICs and HPV vaccines have further improved cervical cancer prevention prospects. While existing screening programs in high-income countries should be re-organized, in view of the downstream effects of national HPV vaccination programs, LMICs should introduce national programs to vaccinate single year cohorts of girls aged 9-13 years with two or three doses and screen 30-35-year-old women with HPV testing to pragmatically decrease their high disease burden.

Infection transmission and chronic disease models in the study of infection-associated cancers

In the last three decades, the appreciation of the role of infections in cancer aetiology has greatly expanded. Among the 13 million new cancer cases that occurred worldwide in 2008, around 2 million (16%) were attributable to infections. Concurrently, the approach to prevention of infection-related cancers is shifting from cancer control to infection control, for example, vaccination and the detection of infected individuals. In support of this change, the use of infection transmission models has entered the field of infection-related cancer epidemiology. These models are useful to understand the infection transmission processes, to estimate the key parameters that govern the spread of infection, and to project the potential impact of different preventive measures. However, the concepts, terminology, and methods used to study infection transmission are not yet well known in the domain of cancer epidemiology. This review aims to concisely illustrate the main principles of transmission dynamics, the basic structure of infection transmission models, and their use in combination with empirical data. We also briefly summarise models of carcinogenesis and discuss their specificities and possible integration with models of infection natural history.