Methods used for immunization coverage assessment in Canada, a Canadian Immunization Research Network (CIRN) study

Figures & data

Table 1. Methods used for immunization coverage assessment, by P/T.

	NWT	BC	AB	SK	MB	ON	QC		NS	NL	PEI	NB
Measures up-to-date coverage	^✓	^✓^1	^✓	^✓	^✓	x	^✓		^✓	^✓	^✓	^✓
Measures on-time coverage	^✓	^✓	x	^✓	^✓	x	^✓^2		x	x	x	x
Measures coverage using other method(s)	x	^✓^3	^✓	x	x	^✓^4	x		x	x	x	x
Coverage definition includes valid doses only	valid	valid	valid	valid	valid	valid	valid and all^5		valid	valid	all	valid
Grace period^6 considered for valid dose assessment	n/a	x	^✓	^✓	^✓	x	x		x	x	n/a	^✓
Denominator data source for coverage assessment	HI and statistics bureau	Mixed^7	HI	Mixed^8	HI	SL	Mixed ^9		SL	SL	Mixed^10	SL
Age milestones for assessing coverage	2 yr.	2 , 7 yr.	2 yr.	2, 7 and 17 yr.	1, 2,7, 11 and 17 yr.	7, 12,13 and 17 yr.	15 and 24 mo.		x	2 yr.	2 yr.	School entry (4-5 yrs)
Grade milestones for assessing coverage	x	Grade 6 and 9	Grade 1 and 5	x	x	x	Grade 4 and 9		Grade 7	Grade 4, 6 and 9	Grade 1, Grade 6 and 9	Grade 7 and 9
Exceptions to coverage measurement	x	Influenza, Hepatitis A	x	x	x	Influenza Rotavirus^11		x	childhood vaccines	Influenza,	Influenza	Influenza, childhood vaccines
Frequency of coverage measurement	bi-annually	annually for all age groups	annually	quarterly (age 2 and 7), annually for other ages	annually	annually	bi-annually, annually^12		annually	annually	annually	annually

✓ denotes yes; x denotes no; n/a denotes not applicable; HI denotes health insurance; SL denotes school registration lists

¹ British Columbia assesses up-to-date coverage for all recommended vaccines for the 2 and 7 year old milestones, and assessment of vaccines scheduled for administration in Grade 6 and 9.

² Quebec assesses on-time coverage using a coverage survey for 15 and 24 month olds.

³ British Columbia has used IDEA score periodically to examine timeliness of immunization among 2 year olds.¹¹

⁴ Ontario has historically used a “complete-for-age’ definition. The exception is the method used for measles-mumps-rubella vaccine, which identifies the proportion of students who have received one or two doses of MMR vaccine by antigen.

⁵ Quebec assesses coverage for 15 and 24 months olds using a coverage survey, reporting two different estimates: one based on valid doses only and the other based on all doses. Coverage calculated from the provincial registry (i.e., measles) considers only valid doses.

⁶ Saskatchewan and New Brunswick apply a four day grace period to valid dose assessment. In Manitoba, a seven day grace period may be applied in certain scenarios. In Alberta, inactivated vaccines given 4 days before the minimum age or 4 days before the minimum interval has elapsed require consultation with the local Medical Officer of Health to determine if the dose is accepted and/or for further scheduling advice.

⁷ Denominator source in British Columbia varies across the health authorities where some regions rely on registry data (as derived from public health records when a person is born in the province or presents themselves to public health after moving from another province) or Ministry of Education enrollment estimates, school class lists or combination of both data sources including information collected on consent forms.

⁸ The denominator source in Saskatchewan is based on the numbers derived from public health records when a person is born in the province or presents themselves to public health after moving from another province).

⁹ Quebec does not have a population-based immunization registry because only those who received at least one dose of vaccine are included in the provincial data. The denominator data source for coverage assessed among Grade 4 and 9 students is the number of students attending school each year. The exception is a measles vaccine registry which includes the Quebec population born on and after 1970, based on the following information sources: health insurance database, Ministry of Education student database. In addition, a coverage survey is used to assess toddler immunization coverage (15 and 24 months old). The sampling frame for the coverage survey is the provincial health insurance database.

¹⁰ PEI uses the discharge abstract data or perinatal database to identify infants born in PEI (all babies are born in the hospital with very few exceptions) and uses data from the Department of Education for school age indicators.

¹¹ The first birth cohort eligible for publicly-funded rotavirus vaccine has not yet reached the aged of routine coverage assessment in Ontario (age 7 years). When this occurs in the 2019-20 school year, rotavirus coverage will be assessed through routine processes. Other processes (i.e. doses distributed) are being used in the interim.

¹² Quebec assesses coverage on a bi-annual basis for the 15 and 24 month olds. Coverage is assessed in grade 4 and 9 for Hepatitis B and HPV on an annual basis.

Figure 1. Comparison of immunization coverage estimates reported by select Canadian Provinces and as estimated by the 2013 childhood National Immunization Coverage Survey (cNICS): Measles

Notes:

1. Two-year old immunization coverage data for the Regional Health Authority of Vancouver Coastal Health are not included within the provincial estimate because coverage for this region is assessed periodically using survey methods.

2. Coverage estimates for Saskatchewan are based on children who were registered in the Saskatchewan Immunization management System (SIMS) and with provincial health coverage at the time of assessment.

3. Manitoba coverage estimates can be found online: http://www.gov.mb.ca/health/publichealth/surveillance/mims/docs/2012.pdf.

4. The reference birth cohort used by Quebec is children born between Oct 1, 2011 and Dec 31, 2011 and evaluated at 24 months of age in 2014.

5. The birth year cohort for the assessment of 2-year-old measles coverage in PEI are those born within the province during the 2011/12 fiscal year.

6. Immunization coverage for measles at 7 years-of-age in British Columbia is derived from Panorama and the immunization registry in use in Vancouver Coastal Health (PARIS). In three regional health authorities, Ministry of Education data is used for denominator estimates.

7. The exception to Ontario's 'complete for age' coverage methodology is the ability to report on coverage for measles, mumps and rubella by number of doses. Two doses measles coverage estimates are presented for the birth cohorts of 1995 and 2005 who were 7 and 17 years of age in the 2012-13 school year, respectively.

8. The coverage definition used by PEI is the receipt of 2 doses of measles-containing vaccine by the 6^th birthday.

Figure 2. Comparison of immunization coverage estimates reported by select Canadian Provinces and as estimated by the 2013 childhood National Immunization Coverage Survey (cNICS): Pertussis

Notes:

1. Two-year old immunization coverage data for the Regional Health Authority of Vancouver Coastal Health are not included within the provincial estimate because coverage for this region is assessed periodically using survey methods.

2. Manitoba coverage estimates can be found online: http://www.gov.mb.ca/health/publichealth/surveillance/mims/docs/2012.pdf

3. Quebec assessed coverage for children born between Oct 1 and Dec 31, 2011 using a coverage survey. The coverage definition used was receipt of at least 4 valid doses, with validity of doses assessed in relation to a minimum age at first dose and minimum intervals between doses.

4. The 2011-2012 fiscal year birth cohort was used in PEI and this only includes those born in PEI.

5. Immunization coverage for measles at 7 years-of-age in British Columbia is derived from Panorama and the immunization registry in use in Vancouver Coastal Health (PARIS). In three regional health authorities, Ministry of Education data is used for denominator estimates. Coverage is defined as 4th or 5th dose of diphtheria/acellular pertussis/tetanus and 3rd or 4th dose of polio after the fourth birthday and by the 7th birthday.

6. Ontario has historically calculated 'complete for age' coverage, which represents the proportion of students who are not yet 'overdue' for a particular immunization. For the cohort assessed, the pre-school booster was considered valid if given on or after the age of three years and nine months.

7. PEI assesses coverage by agent. Coverage among 7 year olds reflects administration of the Tdap-IPV pre-school booster administered between the ages of 4 and 6 years.

8. Ontario has historically calculated 'complete for age' coverage, which represents the proportion of students who are not yet 'overdue' for a particular immunization. For the cohort assessed, the pre-school booster was considered valid if given on or after the age of three years and nine months.

Table

Term	Definitions^5	Example
Up-to-date coverage	Up-to-date immunization coverage refers to assessing coverage in a specific age-cohort in relation to how many doses of vaccine have been received by a particular milestone age. The number of doses is informed by NACI recommendations and the relevant P/T immunization schedule.	≥ 4 doses of pertussis-containing vaccine by the 2^nd birthday (numerator definition)
On-time coverage	On-time immunization coverage refers to the proportion of children in a particular age cohort who have received all valid doses required to be on-time and up-to-date by specific milestone ages (typically by the first or second birthday). The assessment is made examining doses for multiple vaccine series, as per the routine schedule. Thus, even if one dose of a particular antigen is late, the child will not be considered on-time. In practice, a leeway period is often used for calculating on-time coverage (i.e., a 1 month leeway period after the recommended date for vaccine administration).	All doses for all recommended vaccines (as per the P/T schedule) administered within 1 month of recommended interval by the 2^nd birthday (numerator definition)
Minimum interval	The minimum interval of time recommended between 2 vaccine doses to allow for the body to mount an appropriate immune response before the subsequent dose is received. Minimum intervals are typically shorter than the recommended spacing of vaccines outlined within routine immunization schedules. Minimum intervals are informed by NACI or other (e.g., ACIP) expert body recommendations.	1 month (defined as 28 days) between doses of live virus vaccines
Valid/invalid dose	A valid dose is one that is delivered in accordance with decision support rules outlining the minimum age recommended for vaccine administration and/or the minimum time interval between 2 doses of vaccine. Doses that are administered too early (before the minimum age and/or before the minimum interval has elapsed) are considered invalid and are not typically ‘counted’ in the dose assessment used for coverage assessment.	A child who receives MMR vaccine at 12 months of age and again 14 d later would be regarded to have received only 1 valid dose of MMR. The second dose was administered before the minimum interval and is considered invalid.
Grace period	When used, grace periods provide an allowable period before dose eligibility such that an administered dose can still be considered valid.	If a 4 day grace period is used, doses of MMR administered up to 4 d before a client turns 1 y of age, would be considered valid doses for the purposes of coverage assessment (assuming 12 months of age is used as the minimum age)

Note: To generate a coverage estimate, the numerator (of children with the requisite number of valid doses) is divided by the eligible population (denominator). For coverage assessment, the numerator is divided by the denominator, which CIRC defines as all children within a defined birth cohort who are current residents in the P/T during the time period of interest (not only those who present for immunization).⁵

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