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The evaluation of HPV immunization programs over time is extremely important, given the need to evaluate impact over the long term and, as with many other vaccine programs, the unknown duration of protection at the start of implementation. Monitoring and evaluating HPV immunization programs will require standardized HPV testing methods, standardized units of measurement for HPV antibodies, population-based reporting systems for HPV-associated diseases, and registries or information systems for follow-up of vaccine coverage(21,74). Effective linkage between the latter databases will also be important. Regular studies of the knowledge, attitudes and practices of the public and health professionals will also be necessary.
At a national level, much effort is still required to prepare for the evaluation of new HPV immunization programs, and few data are available in the literature (Appendix 3 presents the literature review). Infection with HPV is not reportable in any province or territory of Canada, so it is difficult to know the prevalence, incidence or distribution of HPV genotypes in the population(75). As for all immunization programs, provincial and national authorities will require a detailed evaluation plan for HPV vaccination programs. Significant investments have to be made to conduct surveillance and program evaluation over the long term, and a multidisciplinary approach is needed.
As with other health care programs, immunization is primarily a provincial and territorial responsibility. The Canadian Immunization Registry Network (CIRN) and the F/P/T working group of the CIC have been working together for the past 6 years to develop a national network of immunization registries across the country. CIRN has developed the standards and guidelines for a commonly used methodology to measure coverage routinely using registry data. Currently, five provinces have fully functional registries, and the remaining jurisdictions are either planning or evaluating the immunization module contained in INFOWAY’s PANORAMA public health surveillance system. In the meantime, there are several options for measuring coverage. The Adult and Childhood National Immunization Coverage Survey, conducted every 2 years, provides national estimates for 17-year-olds in the childhood survey and for the adult population. However, the concern with these studies is that they are not able to assess subpopulations and that non-participation bias cannot be excluded. Another alternative is to use provinces with established immunization and cancer screening registries as special pilot sites. This approach would enable a more comprehensive assessment of vaccination coverage, but data extrapolation to other provinces and territories may not be appropriate.
Vaccinating adolescents or adults presents more barriers than vaccinating young children. Because the HPV vaccine is recommended for adolescents and young adults, existing school-based immunization programs may require expansion, and the development of new immunization systems for young adults might be needed.
It is imperative to establish an HPV type distribution baseline that is representative of different populations across Canada and to follow this up with a long-term surveillance program to monitor the impact of HPV vaccination against types 16 and 18 (6 and 11) on the overall incidence and prevalence of HPV infections. Ultimately, this surveillance system may reflect shifts in HPV type distribution as a result of vaccination against types 16 and 18 (6 and 11), such as an increase in types not included in the vaccine.
Planning for a national HPV sentinel surveillance system is under way. Surveillance includes repeated cross-sectional anonymous surveys of women (and/or men) recruited across Canada, linked to cervical/cervico-vaginal (and/or anal) specimens collected by a health care provider. This surveillance system will provide baseline data on the distribution of HPV subtypes in selected sites and populations across Canada in order to monitor the incidence and prevalence of type-specific HPV infections, to identify potential risk factors associated with high-risk HPV infection and to correlate the distribution of HPV types with cytological outcomes and socio-demographic and behavioural risk factors.
Although cervical cancer is the most important long-term health outcome, other endpoints are needed to monitor the short- and mid-term impact of vaccination on HPV-related infections. Malignancies develop slowly, and although cancer registries are available they will be useful only years after the implementation of HPV immunization programs. Endpoints used in clinical studies could be used as short- and mid-term evaluation outcomes. A consensus report from a World Health Organization expert group proposed histologically confirmed high-grade CIN or worse (including cervical cancer) as an acceptable surrogate endpoint(20,21,72). Monitoring of cervical lesions will require development of population-based reporting systems for HPV-associated infections(74). Type-specific persistence of infection (the presence of the same HPV type at two or more consecutive visits separated by 6-12 months) could also be an outcome measure(21). However, commercial tests for HPV testing and typing are not yet routinely available in the Canadian public health system.
Evaluation plans should also monitor the HPV vaccination impact on cervical cancer screening practices (decline in the burden of screen-detected precursor lesions requiring follow-up and treatment, new algorithms, etc.) and on continued screening compliance in HPV-vaccinated women.
In Canada, the public health burden of condylomas is not known, nor are there registries to measure their incidence or prevalence. Studies are needed to evaluate the prevalence and incidence of this disease.
Indeed, measuring the impact of the immunization program on HPV-associated diseases and on screening practices will require important efforts. A baseline assessment of HPV-associated diseases (including those caused by types not covered by the vaccine), of screening practices and of costs could be useful during the implementation of vaccination programs(74). To detect a possible replacement in circulating HPV types, a surveillance system should be developed.
Even without national/provincial electronic immunization registries, it will be essential to be able to contact HPV-vaccinated women if an additional dose of the vaccine is needed. Relying on mass media and communication to professionals to disseminate information about the need for a booster dose would be less effective than individualized notification. Specific modalities to inform health authorities about HPV vaccine status will have to be organized before HPV program implementation.
Canada Health Infoway supports the development of the Pan-Canadian Electronic Health Record, as well as the standardization of laboratory data (to ensure that data can be exchanged among systems), including cytopathology data.
The immunization management module of the future PANORAMA public health information system could provide data on the HPV vaccination status of residents in each Canadian jurisdiction if the vaccine is provided by public health providers or if the information about the vaccination is reported by private providers to public health authorities.
In the meantime, it may be possible to link existing regional/provincial databases (immunization and cancer) for evaluation. Also, national immunization rates can be measured using the Adult and Childhood National Immunization Coverage Survey or by aggregating coverage estimates from the jurisdictions once the national coverage standards are adopted(76). The possibility of restricting certain aspects of the evaluation to predetermined geographic areas could be explored. Additional data from these areas could facilitate future decision-making on the prevention of HPV infections and related anomalies.
To conclude, evaluation of the HPV vaccination program will be crucial and complex. Evaluation requires the development of a comprehensive plan and will demand significant resources.