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Volume 31-09  1 May 2005

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ARCHIVED - National Standards for Immunization Coverage Assessment: Recommendations from the Canadian Immunization Registry Network

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Across Canada, universal immunization programs are provided for the routine administration of childhood immunization against diphtheria, pertussis, tetanus, poliomyelitis, Haemophilus influenzae type b, measles, mumps, rubella, and hepatitis B infections(1). In recent years, new programs have been introduced in Canada based on recommendations from the National Advisory Committee on Immunization (NACI), including varicella vaccination, pneumococcal conjugate and meningococcal conjugate vaccination, influenza vaccination and acellular pertussis vaccination for adolescents. Each vaccine is administered at various ages, according to NACI recommendations and provincial/territorial immunization schedules. Immunization coverage rates are needed to monitor vaccine uptake levels in the population. Coverage is considered an important health indicator because it is a sensitive measure of the susceptibility of a population to vaccine-preventable diseases and can be used as a proxy measurement to evaluate health services, systems, and interventions(2,3).

Immunization coverage information is often collected and reported at local, provincial/territorial, and national levels. Currently, there are no national standards for the reporting of immunization coverage in Canada. Comparison of coverage rates among jurisdictions and aggregation of jurisdictional estimates for national reporting are challenged by i) a lack of regular and consistent data collection, ii) differences in coverage assessment methods, iii) a lack of standardized reporting definitions, and iv) heterogeneity among jurisdictional immunization schedules. Defining national standards for immunization coverage reporting would function to accomplish the following:

  1. identify populations across Canada with low immunization coverage in order to determine factors associated with low coverage and to target public health interventions(4);

  2. monitor national immunization coverage trends over time, thus contributing to the evaluation of programs and progress towards the achievement of targets(4);

  3. facilitate sharing of immunization information among federal/provincial/territorial jurisdictions while enhancing the reporting capabilities of immunization registries or other information systems;

  4. contribute to the development of a fully operational Immunization Registry Network, a key objective of the National Immunization Strategy (5).

This report will outline national standards for the reporting of immunization coverage across Canada.

Methods

A survey was completed by provincial/territorial representatives of the Canadian Immunization Registry Network (CIRN) on the standards used for provincial/territorial coverage reporting. The results of the survey were presented at the CIRN meeting, sponsored by Health Canada (HC) (now Public Health Agency of Canada), in Vancouver on 6 and 7 July 2004. During the meeting, key objectives for reporting immunization coverage were discussed, and recommendations for reporting of national immunization coverage were drafted. In addition to the survey, a literature review of national and international coverage assessment contributed to these deliberations, the results of which are in the full report (available from PHAC).

Results

Frequency and time of year of assessment

Frequency and time of year of assessment depend on the methods used to measure immunization coverage. While some jurisdictions operate fully functional registries, others rely on survey methods to obtain population-based coverage estimates. Eleven jurisdictions using surveys and/or registries assess immunization coverage annually at various times of the year, depending on the vaccine under investigation. Two jurisdictions use survey methods to assess coverage every other year. Of the jurisdictions with fully functioning registries, two assess quarterly each year and one assesses monthly.

HC assessed childhood immunization coverage in 2002 and 2004 using the National Immunization Coverage Survey (NICS). The NICS will be repeated every 2 years until a national immunization registry network is fully operational.

Age cohorts and populations

Nine jurisdictions report separate estimates of routine childhood immunization coverage for 2-year-olds (assessed at or by the 2nd birthday), six assess children at school entry (4 to 6 years of age) and three assess 1-year-olds (at or by the 1st birthday).

Influenza and pneumococcal conjugate immunization coverage is assessed for specific at-risk populations. Ten jurisdictions assess adults>= 65 years old or with high-risk medical conditions, four assess health care workers, three assess long-term care residents, and one assesses the general adult population. A 2001 PHAC survey assessed adults>= 18 years of age. Specific cohorts of interest included adults>= 65 years, those with high-risk medical conditions, and health care workers.

Agent/antigen-specific coverage

As with age cohorts, the vaccine antigen or agent selected for evaluation differs according to the immunization schedule. Five jurisdictions report antigen-specific coverage (e.g. diphtheria, tetanus, pertussis, influenza), and nine jurisdictions collect and report by agent (e.g. Pentacel?, MMR, DaPT/IPV) when possible. National surveys, sponsored by PHAC, collect and report coverage by specific vaccine antigen.

Up-to-date or on-time immunization

Up-to-date immunization is assessed in most jurisdictions, and complete coverage is defined according to the immunization schedule. Three jurisdictions assess on-time immunization by measuring age at the date of immunization. The NICS assesses up-to-date and on-time coverage (median age in months at receipt of each vaccine dose) for each childhood vaccine.

Recommendations for reporting of national immunization coverage

Frequency and time of year of assessment

While immunization registries are under development, it is recommended that national coverage assessment and reporting occur every 2 years. In addition, each jurisdiction should assess and report immunization coverage annually. An annual national immunization report compiled by PHAC will include coverage estimates from both the NICS and the jurisdictional assessments with an addendum detailing the methodology and definition of age cohorts.

Once immunization registries are fully functioning nationally, it is recommended that coverage data be reported from registry records on an annual basis. Registries should maintain the capacity to report more frequently as needed for program planning and evaluation, and for consideration of new immunization programs.

The time of year of assessment is based on the age cohorts under consideration. Coverage reporting for 2-year-old children may be based on assessment of routine childhood immunizations at any time of the year; however, it is recommended that school-age children be assessed at the end of the school year to capture coverage resulting from school immunization campaigns. Coverage reporting for adults should be based on assessment every 2 years, in the spring after the influenza season.

Age cohorts and populations

In order to report age-specific immunization data, it is essential to capture the date of birth and the date of immunization. Assessment of national immunization coverage should produce estimates at 2 years old (by the 2nd birthday), 7 years old (by the 7th birthday), and 17 years old (by the 17th birthday). Estimates obtained from surveys should be based on a sufficient and representative 12-month cohort for each age milestone.

Assessment of immunization coverage for adults should produce coverage estimates for those>= 18 years of age and should be based on the NACI-recommended adult immunization schedule. Assessment of more specific age or population cohorts should be determined according to vaccine-specific NACI recommendations.

Agent/antigen specific coverage

It is recommended that immunization coverage information be collected by agent, when possible, and reported by specific antigen for recommended vaccines. Attention must be paid to any changes of product provided nationally and/or provincially in order to accurately reflect immunization coverage.

Up-to-date and on-time immunization

Reporting of national immunization coverage should be based upon up-to-date immunization status, which is defined as receipt of the full number of vaccine doses for the 2-year, 7-year, and 17-year milestones according to the immunization schedule recommended by NACI. Because of age-specific differences among the jurisdictional immunization schedules, on-time immunization should be reported separately by each province and territory.

Conclusion

The draft standards for reporting of national immunization coverage are based on a comprehensive review of international and national reporting standards and were agreed upon by consensus among CIRN members. Defining standards for reporting of national immunization coverage is an important step towards achieving optimal information flow and comparability of jurisdictional and national immunization coverage estimates.

References

  1. Gyorkos TW, Franco ED, Tannenbaum TN et al. Practice survey of immunization in Canada. Can J Public Health 1994;(Suppl 1):31-6.

  2. Bolton P, Hussain A, Hadpawat A et al. Deficiencies in current childhood immunization indicators. Public Health Rep 1998;113(6):527-32.

  3. Bos E, Batson A. Using immunization coverage rates for monitoring health sector performance: Measurement and interpretation issues. Washington: The International Bank for Reconstruction and Development/The World Bank, 2000.

  4. Childhood Immunization Division, Bureau of Communicable Disease Epidemiology and the Canadian Paediatric Society. Guidelines for assessment of vaccine coverage in children. CCDR 1993;19:180-2.

  5. Advisory Committee on Population Health and Health Security. National Immunization Strategy: final report 2003. Ottawa: Minister of Health, 2004.

Source: K Haimes, MHSc (candidate), University of Toronto; H Schouten, RN, MHSc, Federal Co-Chair Canadian Immunization Registry Network, T Harris, RN, MHSc, and L Belzak, MHSc, acting Federal Co-Chair Canadian Immunization Registry Network, Public Health Agency of Canada; and members of the Canadian Immunization Registry Network: C O'Keefe (Newfoundland and Labrador), J Scott (Nova Scotia), R McEachern (Prince Edward Island), L Cocharane (New Brunswick), N Boulianne (Quebec), B Kawa (Ontario), T Mawhinney (Manitoba, Provincial/Territorial Co-Chair), R Tuchscherer (Saskatchewan), E Sartison (Alberta), M Naus (British Columbia), C Hemsley (Yukon), M Bell (Northwest Territories), C Palacios (Nunavut), S Taylor-Clapp, U Auguste (First Nations and Inuit Health Branch, Health Canada), R Pless, (Public Health Agency of Canada), S Lavigne (Correctional Services Canada).


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