ARCHIVED - MEASURING UP: RESULTS FROM THE NATIONAL IMMUNIZATION COVERAGE SURVEY, 2002

 

Background

Immunization is considered to be among the most cost-effective public health interventions available(1). High levels of immunization coverage are required to prevent and control vaccine-preventable diseases. Immunization coverage rates are considered a sensitive indicator of the health of a population and the capacity of a health system to deliver essential services(2), and their measurement is required to monitor programs and progress towards national immunization targets. If measured on an ongoing basis, coverage rates can be used to detect changes in the impact of immunization programs and identify underimmunized subpopulations(2).

In Canada, immunization policy development and program delivery are the responsibility of provinces and territories(3). Therefore, immunization coverage information is collected at the provincial and territorial level using varied coverage assessment methods. Provincial and territorial comparisons are difficult because of the variability of immunization schedules and absence of national standard definitions of numerators and denominators.

In 1994 and 1996, surveys were mailed to households across Canada in order to assess national immunization coverage among 2-year-olds(4,5). This method was repeated in 1998 with the addition of households containing 7-year-old children(6). Coverage for the 2-year-old cohort was estimated in two ways: coverage at 2 years of age based on all vaccine doses received for comparison with previously surveyed cohorts, and coverage by the second birthday based on vaccine doses received before or on the date of the child's second birthday for evaluation of national targets for vaccine coverage. Coverage estimates for the 7-year-old cohort were based only on immunizations received by the seventh birthday (i.e. vaccine doses received before or on the date of the child's seventh birthday).

At the same time as surveys were used to assess coverage, there was recognition at the national level that a system of immunization registries was required to electronically capture coverage data in real time(7). As there is still variability in the use of electronic recording of immunizations across the country, surveys are required to obtain this important information.

In the absence of a comprehensive provincial/territorial immunization registry network, a review of the literature was conducted in 2002 in order to find the best method to conduct national coverage assessment. Given the constraints of time and resources, it was decided that a telephone survey was the best method to determine whether children in Canada were immunized according to the National Advisory Committee on Immunization (NACI) schedule for routine immunization.

The objectives of the 2002 survey included the following:

  • Determining the availability of immunization records in the home.
  • Estimating the national and provincial/territorial routinely recommended immunization coverage rates of children at ages 2 and 7.
  • Determining the timeliness of immunization coverage.
  • Assessing parental knowledge and attitudes towards childhood immunization.
  • Assessing missed opportunities for childhood immunization.
  • Determining whether immunization records should be accessible on the Internet.
  • Determining the acceptance of immunization in the event of a bioterrorist threat.
  • Providing the World Health Organization and the Pan American Health Organization with diphtheria-pertussis-tetanus immunization rates among children at 12 months of age.

Methods

In 2002, MacArthur and Schouten conducted a literature review to evaluate past and current methods used to assess immunization coverage in Canadian populations and to critically appraise the validity of each measurement tool .* It was recommended, given budgetary and time constraints, that surveys were the most feasible, cost-effective method of repeatedly reporting on the immunization status of the Canadian population. Health Canada developed a survey in consultation with the National Immunization Coverage Survey Advisory Group,** and an outside polling agency, Ipsos-Reid, was contracted to pre-test and interview respondents to collect immunization coverage data.

As the 2-year-old cohort is estimated to be only 2.5% of the Canadian population, a convenience sample was used. The respondents were selected from the Ipsos-Reid's Canadian Household Panel. Eligible households were those that included a child between 24 and 36 months of age or a child who was between 7 and 8 years of age as of the date of survey administration. Respondents were selected from seven regions (British Columbia, Alberta, Manitoba and Saskatchewan, Ontario, Quebec, the Atlantic provinces, and the territories). Trained interviewers conducted computer-assisted telephone interviews in both English and French from 17 October to 6 November, 2002. Interviewers were required to make seven attempts before disqualifying or replacing an otherwise eligible respondent. Questions were asked of the member of the household who was reported to be most familiar with the child's immunization history. Arrangements were made for a more convenient interviewing time if that member was not available.

Data extraction and preliminary data analysis were performed by Ipsos-Reid using SPSS (Statistical Package for the Social Sciences), and responses were weighted using demographic factors. Respondents who did not have a copy of their child's immunization record at the time of interview answered questions regarding their child's immunization history from recall. With the respondent's permission, Health Canada re-contacted 217 respondents in order to gather immunization on the history from records obtained by parents from their physician or local public health agency. Analysis was completed by Health Canada using SPSS 11.5 and the results are presented below.

Results

Information was collected for 629 2-year-olds (51.0%) and 602 7-year-olds (49.0%). The respondents were mostly mothers (n = 991, 80.5%) but also included fathers (n = 233,18.9%), grandparents (n = 2, 0.2%), step-parents (n = 3, 0.2%), guardians (n = 1, 0.1%), and other relatives (n = 1, 0.1%).

The distribution of respondents by region approximately represents the actual distribution of the Canadian population with the exception of the Northwest Territories, the Yukon Territory, and Nunavut (Table 1). The territories are underrepresented in the survey, and only limited conclusions may be made about coverage rates based on this sample.

Table 1. Unweighted distribution of respondents by child's age and region

Number
of 2-year olds

Number
of 7-year-olds

Total
number of respondents

Provincial/territorial percentage of survey sample (%)

Provincial/territorial
percentage of total
Canadian population* (%)

BC

92

74

166

13.5

13.2

Alberta

92

50

142

11.5

9.9

Saskatchewan
and Manitoba

56

64

120

9.7

6.9

Ontario

189

200

389

31.6

38.4

Quebec

147

142

289

23.5

23.7

Atlantic Provinces

36

49

85

6.9

7.5

Territories

17

23

40

3.2

0.3

TOTAL

629

602

1231

100.0

100.0

*Statistics Canada: Canadian Census 2002


The majority of parents stated that their child had received an immunization (n = 1213, 98.5% ± 0.7%), and there was no significant difference between responses from parents of 2-year-olds (98.2% ± 1.0%) and 7-year-olds (99.0% ± 0.8%). There were no significant differences in responses of reported immunization by age of child, region, family income, or education. There were a few respondents who stated that their child had never been immunized (n = 17, 1.4% ± 0.6%), and vaccine safety was the most frequently stated reason (48.0% ± 19.6%).

Availability of Immunization Records in the Home

Most parents whose child had been immunized had a copy of the immunization record (85.0% ± 2.0%) in the home. Parents of 2-year-olds (84.8% ± 2.8%) and parents of 7-year-olds (85.3% ± 2.8%) were equally likely to have a copy of the immunization record; however, parents aged > 45 (n = 57, 77.2% ± 10.0%) were less likely to have a copy than parents aged < 25 (n = 42, 88.1% ± 9.7%). Fathers (75.2% ± 5.6%) were less likely than mothers (87.4% ± 2.1%) to report having a copy of the immunization record.

When asked to state the main reason why they did not have a copy of their child's immunization record, most parents (52.6%) said that they had a copy but did not have access to the record at the time of the telephone call.

Other reasons given for not having a record included the fact that their doctor kept a copy (18.6%), they had one but they lost it (13.3%), or they were never given a copy (5%).

Routine Recommended Immunization Coverage Rates of Children at Ages 2 and 7

National coverage was estimated using the immunization history from a record in the home either during the initial interview or during a follow-up telephone interview. Records were obtained orally for 521 2-year-olds and 459 7-year-olds (79.5% of the 1231 respondents initially contacted).

2-year-olds

Table 2 presents the frequency of total reported doses given to 2-year-olds for diphtheria, pertussis, tetanus, polio, and Haemophilus influenzae (Hib). Shaded cells indicate the percentage of 2-year-olds reported to have received the NACI recommended number of doses(8).

Table 2. Two-year-olds: national immunization coverage by reported dose for diphtheria, pertussis, tetanus, polio, and Haemophilus influenzae type B (n = 521)

Immunization

Percentage of respondents indicating total number of doses received according to parental records (%)*

0

1

2

3

4

Diphtheria

3.0

97.1

95.0

93.3

76.8

Pertussis

4.4

95.6

93.5

90.9

75.2

Tetanus

4.5

95.6

94.1

91.6

74.3

Polio

7.4

92.6

90.3

87.7

 

Hib

12.0

88.0

85.4

83.2

64.0

*95% confidence limits range between ± 1% and ± 4.1%.

From parental records, it is estimated that 76.8% of 2-year-olds had received four diphtheria doses, 75.2% four pertussis doses, 74.3% four tetanus doses, 87.8% three polio doses, and 64.0% four Hib doses. There is a significant difference between the reported coverage rates for Hib and the other immunizations (p < 0.0001). Only 58.3% ± 4.2% of the population reported that their children had received all recommended doses of diphtheria, pertussis, tetanus, polio, and Hib according to records available at the time of interview in the home.

Table 3 shows the frequency of total reported doses for 2-year-olds for measles, mumps, and rubella. It is recommended that 2-year-olds have one dose of the measles, mumps, and rubella immunization on or after their first birthday(8).

Table 3. Two-year-olds: national immunization coverage for measles, mumps, and rubella by reported dose (n = 521)

Immunization

Number of doses reported by parental records (%)*

0

1

Measles

5.5

94.5

Mumps

6.5

93.5

Rubella

6.4

93.6

*95% confidence limits range between ± 1% and ± 4.1%.

From parental records, it is estimated that 94.5% of 2-year-olds had received at least one dose of measles vaccine, 93.5% at least one mumps dose, and 93.6% had received at least one rubella dose. Most children received all three immunizations together, and 93.2% ± 2.2% of the population recorded that their child had received the recommended dose for all three immunizations.

Given the small samples for each region, it is difficult to compare the regional estimates. Additionally, there are differences in immunization record-keeping and provision of immunization among regions, contributing to the variability in estimates, which may not be considered comparable for the purposes of this report.

Table 4 demonstrates the results of national coverage surveys for 2-year-olds based on birth cohorts from 1990 to 2000. The previous surveys were mailed household surveys, whereas this most recent one was a telephone survey. Caution should be used in comparing coverage rate results, as there are differences in methods and sample size.

Seven-year-olds

Table 5 presents the frequency of total reported doses received by 7-year-olds for diphtheria, pertussis, tetanus, polio, and Hib, which are routinely administered at the same time. Shaded cells indicate the percentage of 7-year-olds who were reported to have received the NACI recommended number of doses(8).

Table 4. Two-year-olds: national estimates of immunization coverage, 1994 to 2002*

Immunization

Coverage** at 2 years of age by birth cohort surveyed(6)

Doses

1990-91†

1991-92†

1992-93†

1993-94†

1994-95†

1995-96†

1999-2000

Diphtheria

4

84.7

84.0

84.4

87.1

86.8

84.2

76.8

Pertussis

4

80.1

81.6

82.9

84.8

85.2

83.0

75.2

Tetanus

4

82.0

82.5

83.9

85.9

85.1

83.8

74.3

Polio

>=3

89.7

89.0

87.4

89.9

85.8

90.1

87.7

Measles‡

>=1

96.1

97.2

96.2

97.0

96.0

96.2

94.5

Mumps

>=1

92.8

93.6

96.0

96.8

95.9

95.6

93.5

Rubella

>=1

93.0

94.4

96.0

96.7

95.9

95.5

93.6

Hib§

4

-

-

54.6

69.3

73.7

74.9

64.0

*Data on the birth cohorts for the years 1996-97 to 1998-99 are absent because of a gap in survey administration.

**95% confidence limits range between ± 1% and ± 5%.

†Previous surveys were conducted using a mailed questionnaire and coverage rates should not be compared with the current survey, which was conducted by telephone questionnaire.

‡Coverage is based on measles dose received at any time.

§Haemophilus influenzae type B.


Table 5. Seven-year-olds: national immunization coverage by reported dose for diphtheria, pertussis, tetanus, polio, and Haemophilus Influenzae type B from parental records (n = 459)

Immunization

Number of doses received according to parental records (%)*

0

1

2

3

4

5

Diphtheria

2.1

97.9

96.4

93.4

87.7

70.5

Pertussis

4.1

96.0

93.9

90.1

84.1

65.3

Tetanus

3.6

96.3

94.2

91.4

85.0

65.9

Polio

7.9

92.1

84.4

73.2

65.6

 

Hib

11.7

88.4

82.7

78.7

65.2

 
*95% confidence limits range between ± 1% and ± 4.4%.

From parental records, it is estimated that 70.5% of 7-year-olds had received five doses of diphtheria, 65.3% five doses of pertussis, 65.9% five doses of tetanus, 65.6% four doses of polio, and 65.2% had received four doses of Hib. Only 38.5% ± 4.4% of respondents reported that their child had received all recommended doses.

Table 6 shows the frequencies of total reported doses for measles, mumps, and rubella for 7-year-olds. It is recommended that 7-year-olds receive two doses of measles, mumps, and rubella vaccine after their first birthday(8).

Table 6. Seven-year-olds: national immunization coverage for measles, mumps, and rubella by reported dose (n = 459)

Immunization

Number of doses received according to parental records (%)*

0

1

2

Measles

4.3

95.7**

75.8

Mumps

4.4

95.6**

73.8

Rubella

4.3

95.7**

75.6

*This estimate is based on the 444 7-year-olds for whom data were collected in 2002.

**95% confidence limits range between ± 1% and ± 4.4%.


From parental records, it is estimated that 75.8% of 7-year-olds received at least two doses of measles, 73.8% at least two doses of mumps, and 75.6% at least two doses of rubella. Most children received all three immunizations together, and 73.2% ± 4.1% of the sample recorded that their child had received the recommended doses for all three immunizations.

Only 32.5% ± 4.3% of respondents reported that their 7-year-olds had received all recommended doses of diphtheria, pertussis, tetanus, polio, measles, mumps, rubella, and Haemophilus influenzae type B according to their records. For only 38.5% ± 4.4% of the 444 parents who believed that their child was up to date for all immunizations had their children actually received all the recommended doses.

Table 7. Seven-year-olds: national estimates of immunization coverage

Immunization

Percentage coverage* at 7 years of age by birth cohort surveyed(6)

Doses

1989-90**

1990-91**

1994-95

Doses

1989-90**

1990-91**

1994-95

Diphtheria

4

94.5

96.9

87.7

5

78.7

81.0

70.5

Pertussis

4

90.9

95.3

84.1

5

74.9

78.9

65.3

Tetanus

4

93.1

96.0

85.0

5

76.8

79.6

65.9

Polio

>=3

95.4

96.9

73.2

>= 4

85.1

90.8

65.6

Hib†

>=1

86.2

87.7

-

>= 4

-

-

65.2

Measles‡

1

55.9

66.5

95.7

2

   

75.8

Mumps

1

96.7

96.4

95.6

2

   

73.8

Rubella

1

97.2

96.8

95.7

2

   

75.6

*95% confidence limits range between ± 1% and ± 5%.

**Coverage is by the seventh birthday and is based on only those vaccine doses received before or on the date of the child's seventh birthday.

Haemophilus influenzae type B

‡Coverage based on measles dose received at any time

On-time Immunizations

Table 8 presents the median age at which each immunization was received as well as the range of ages that were reported. Median age was calculated only for those individuals for whom age data were available (n = 444, 2-year-olds and n = 471, 7-year-olds). According to the median ages, the immunizations were received in compliance with the recommended schedule. Parents of children in both the 2-year-old (n = 18, 3.5% ± 1.6%) and 7-year-old (n = 26, 5.7% ± 2.1%) cohorts reported that their children had received the first dose of measles immunization before their first birthday (51 weeks or earlier), against NACI recommendations(8).

Table 8. Median age in months at which dose was received according to parental records (n = 915)

Median age in months (range*)

Diphtheria, pertussis, tetanus, polio and Hib

Dose #1
Dose #2
Dose #3
Dose #4
Dose #5
2.1 (1.8-3.0)
4.2 (3.7-6.0)
6.3 (5.7-9.8)
18.6 (17.5-24.3)
60.6 (48.0-75.5)

Measles, mumps, and rubella

Dose #1
Dose #2
12.6 (11.9-18.5)
49.3 (17.5-74.6)
*The weighted range includes the 5th to 95th percentile.

Parental Knowledge and Attitudes Towards Immunization

A series of questions was asked to examine parental knowledge and attitudes towards immunization. When parents were asked to offer a general comment, 33.7% ± 2.1% of those who offered a comment stated that they supported immunizations and that immunizations were beneficial. Additionally, the majority of parents (86.9% ± 1.9%) felt that they had been given enough information about immunization. Parents who believed that their child's immunizations were up to date (88.5% ± 1.9%) were more likely to feel that they had been given enough information than parents who did not think that their child's immunizations were up to date (65.5% ± 12.2%). The most frequently stated barriers to dissemination of information were lack of detailed, complete information providing both benefits and risks (22.4% ± 6.5% ) followed by the respondents' sense that they had not been provided with enough information from a doctor, government, etc. (18.2% ± 5.9% ). When respondents were asked if they had any suggestions to improve the dissemination of information, of those with comments, more suggested the Internet (16.6 ± 2.1%) than other means.

Parents responded that the most frequent source of information on the benefits of immunization were physicians (58.0% ± 1.8%) followed by the media - TV, radio, and newspaper - (20.9% ± 1.2%), family and friends (15% ± 1.1%), and pamphlets (14% ± 1.0%). Residents of Ontario were most likely (75.6% ± 3.9%) and residents of Quebec least likely (31.8% ± 5.2%) to cite a physician as providing information on the benefits of immunization. In Quebec, the most commonly stated source of information was the Centre local de services communautaires (CLSCs) (36.0% ± 5.4%) followed by physicians (31.8% ± 5.2%). Those most likely to have reported receiving information from physicians were parents aged 36 to 45 (64.6% ± 3.9%), parents with some university education (65.4% ± 7.5%), and parents with a family income of greater than $80 000 (66.5% ± 4.8%).

Respondents reported that they had received information on the risks of immunization from a physician (36.9% ± 2.0%) followed by the media - TV, advertisements, newspapers - (27.7% ± 2.5%), and family and friends (15% ± 1.4%). Residents of Ontario were most likely (51.9 ± 4.5%) to report receiving information on risks from a physician, and residents of Quebec were least likely (22.1 ± 4.6%). Residents of Quebec reported receiving information from CLSCs (27.7% ± 5.0%) more often than from a physician. There were no significant regional differences in respondents reporting that they had not received any information on the risks of immunization (p = 0.675). Those most likely to report receiving information on the risks of immunization from a physician were parents aged 36 to 45 (41.4% ± 4.0%), parents with a family income over $80 000 (44.3% ± 3.9%), parents who had taken their child for a well-baby visit or check-up in the previous year (39.8% ± 3.1%), and parents who felt that they had enough information about immunization (38.5% ± 3.0%).

Missed Opportunities for Childhood Immunization

Almost all of the parents interviewed (99.1% ± 0.5%) reported that their child had received the majority of their immunizations in Canada, and there were no significant differences between the 2-year-old and 7-year-old cohorts (p < 0.001). A doctor's office was the most frequent source of immunizations (53.7% ± 2.8%) followed by public health clinics (27.8% ± 2.5%) and CLSCs (13.1% ± 1.9%).

The majority of parents (75.2% ± 2.4%) responded that they had taken their child for a well-baby visit or check-up within the previous year. Seven-year olds were significantly less likely to have had a check-up within that time. Parents from the Atlantic provinces and British Columbia were least likely (68.4% ± 9.3% and 65.4% ± 7.3% respectively) to report having taken the child for a well-baby visit or check-up in the previous year. Less than half of parents (43.8% ± 3.2%) who reported taking their child for a check-up or well-baby visit in the previous year reported that either the doctor or nurse discussed their child's immunization with them. The proportion of parents who had discussed the immunization history with their doctor at the last visit was significantly higher for parents of 2-year-olds (56.0% ± 4.3%) than 7-year-olds (28.4% ± 4.4%).

Less than half of parents (46.7% ± 2.8%) recalled that their child had visited a hospital, emergency department, or special clinic in the previous year. Two-year olds were significantly more likely (54.9% ± 3.9%) than 7-year-olds (38.2% ± 3.9%) to have done so. Only 21.7% ± 3.4% of parents recalled having a doctor or nurse discuss their child's immunization with them at their last hospital, emergency room, or special clinic visit. According to parental report, immunization had been discussed with parents of 7-year-olds (13.4% ± 4.7%) significantly less often than parents of 2-year-olds (27.5% ± 4.4%).

Web-based Immunization Records

Parents were divided (47.5% ± 2.1% approval) as to whether they would like to access their child's immunization records on the Internet through a government Web site on which the records would be confidential and secure. Approval was independent of child's age and region of residence. The most frequently stated reason for supporting Web-based records was that the information would be accessible when needed/parents would not have to rely on others for the information (43.4% ± 4.0%) followed by the fact that Web-based records would be convenient as a backup if current records were lost or misplaced (35.6% ± 3.9%). Respondents who did not support Web-based records most often stated that there is no need for them since the information is already available (53.4% ± 3.6%); they also had concerns about privacy, confidentiality, and security (41.7% ± 3.5%).

Likelihood of Immunization in the Event of a Bioterrorist Threat

Parents were asked whether they would immunize their child for smallpox in the event of a bioterrorist attack. The majority of parents (84.0% ± 2.0%) from both age cohorts indicated that they would immunize in the event of a bioterrorist attack.

Discussion

According to the review by MacArthur and Schouten (unpublished report), telephone surveys are a reliable tool for determining immunization status for both children and adults but are less valid for reporting timeliness of vaccine uptake or date of immunization. More specifically, Duclos and Hatcher(9) found that self-report of influenza immunization status was reliable, although no similar information has been collected regarding self-report for pneumococcal immunizations or for the recommended childhood vaccines. In telephone surveys to estimate immunization coverage, respondents were asked to consult vaccination records/booklets rather than rely on memory alone, as was done in this survey; this served to improve the reliability of the completed questionnaires when compared with physician and/or public health records(5,10). In addition, two previous studies found that over 85% of respondents had access to their child's immunization records at home, as was the case in this survey, whereas only 12% of respondents kept their child's immunization record at the doctor's office or public health clinic(5,10). Therefore, asking parents to consult their child's health record, either at home or at the physician office, during survey completion was a practical objective to estimate immunization coverage.

In an examination of coverage rates for diphtheria, pertussis and tetanus in children at 12 months of age performed for the report to the Pan American Health Organization, immunization coverage is quite high, at 93.3%, 90.9% and 91.6% respectively for both cohorts for the first three doses, recommended at 2, 4, and 6 months of age. However, coverage appears to drop for each subsequent booster dose recommended in both cohorts. The drop in immunization from the third to fourth dose may be an artifact of inaccurate record keeping, as the fourth dose of this series of immunizations is recommended 12 months after the third dose and the fifth dose is recommended at school entry. Caregivers may neglect to bring their child's original immunization record at the time of immunization, and a new record may be created or retained by the provider.

Evidence to support inaccurate record keeping can be found with the significant difference in coverage estimates between diphtheria, acellular pertussis, tetanus, and Hib antigens. These vaccines have been routinely administered in a single dose (Pentacel™, Aventis Pasteur) by all provinces and territories since 1998(6). Inaccurate record keeping of individual antigens was also suspected in the 1998 national coverage survey because of the variability in coverage(6).

More alarmingly, the drop in coverage may be real, due to lack of compliance with the recommended immunization schedule. Parents are often not reminded to update their child's immunization status until school entry and may not be aware or recognize the necessity of the booster at 18 months.

The same phenomenon is evident with measles, mumps and rubella coverage. Estimates for the first dose are high, at around 95%, and very close to achieving the national coverage target of 97.0%(4). Coverage of the second dose of measles-containing vaccine is lower, at around 75%. However, there is no significant difference in the national estimates of individual antigen recording of measles, mumps, or rubella for both cohorts, suggesting that records are kept more accurately for each of these antigens as they are typically provided in a combined product.

Although 98% of respondents reported that their child had been immunized, almost half were not fully immunized according to the NACI recommendations. Parents of only 56.7% of 2-year-olds and 32.5% of 7-year-olds included in this survey reported that all the recommended doses of diphtheria, pertussis, tetanus, polio, measles, mumps, rubella, and Hib had been received. The discrepancy between a parent's belief that their child is fully immunized and the reality may be due to several factors. Parents' recall of their child's immunization history may be inaccurate, and although the child may have been immunized according to the schedule for the first year of life, parents may not be aware of the necessity for booster doses before school entry. Familiarity with the immunization schedule may be difficult for parents, especially when new immunizations are added to recommended list of routine childhood immunizations.

Alternatively, accurate record keeping may be problematic(11). Given the complexity of the immunization schedule and the possibility that immunizations were recorded in a variety of ways within the home, the estimated rates according to records in the home are suspect. It is not uncommon for a parent or child to forget to bring a copy of the immunization record with them to immunization clinics. Clinics may provide a new record to the parent or child or advise them to update records in the home, which may or may not be done appropriately, depending on the level of understanding of immunization or the perceived need to update records in the home. Parents may not feel the need to update their personal records if they believe public health is retaining a record of immunizations on their behalf. There is a body of evidence that immunization coverage decreases with increasing age. Future studies to distinguish whether this decrease is real or an artifact of inaccurate record keeping are required.

Limitations

A decrease in immunization coverage rates was observed for both the 2-year-old and 7-year-old cohorts from the 1998 survey to the 2002 survey. This decrease in coverage should be interpreted with caution, as there was a change in coverage assessment methods.

The type of record consulted when respondents provided their child's immunization history was not captured. Respondents may have read from immunization records issued by governments or health care providers, from records transcribed to their child's baby book, or a combination of these, depending on where or when the immunizations were provided. Records in the home may not have been inclusive of all recommended immunizations.

Parents were not provided with any guidance on how to correctly interpret their immunization record or how to correctly pronounce the immunizations on their record. If the reported immunization history did not include all recommended immunizations, interviewers did not prompt the respondent for specific immunizations potentially missing from their history. This may have caused underreporting of the recorded immunizations, which may have been difficult to read or interpret, or difficult to find on the record. It was evident early in the survey that some respondents had difficulty pronouncing their child's immunizations, particularly Haemophilus influenzae B (Hib). During the pilot of the survey, Hib was frequently interpreted by interviewers as “hepatitis B” or “unknown” until clarified by Health Canada as a discrepancy in data collection.

The ability to increase the sample size at the provincial/territorial level was compromised because of the difficulty in sampling households with 2- and 7-year-old children in Canada. The survey had exhausted the sample of households with 2- and 7-year-old children in the Ipsos-Reid Household Panel, and use of random digit dialling to find more households with these children would have been costly and time-consuming.

The Ipsos-Reid Household Panel is reported to be a good estimate of the general population in Canada. Attitudes, knowledge, and beliefs of high-risk groups for vaccine-preventable disease who are not adequately protected against such diseases may not have been captured in this survey. Further study is required for special populations whose attitudes, knowledge, and beliefs as well as access to health care services may not have been reflected adequately in this survey.

National targets for immunization coverage were developed in 1996 but were not endorsed by all provinces and territories. National targets require review to assess the feasability of achieving the immunization coverage stipulated, and the creation of national standards in order to assess the achievement of national goals and objectives for immunization coverage.

Conclusions

The national immunization coverage survey was designed to estimate national coverage rates for routine childhood immunizations recommended for 2- and 7-year-olds in Canada and at the same time to measure parental attitudes and knowledge about immunization. The results suggest that a telephone survey is an excellent tool for measuring attitudes, knowledge, and beliefs related to immunization and a good measure by which to estimate immunization coverage in the absence of national standards for immunization coverage reporting.

Parents believed their children to be fully immunized, although estimates of immunization coverage in Canada based on records available in the home are lower than the national targets after the first year of life. Future study is required to determine parental knowledge of the recommended schedule of immunizations, availability of immunizations, and the need for reminders.

Parents were satisfied with the amount of information that they had received about immunization, and most had no suggestions for ways to improve dissemination of the information. Physicians were the most important resource for information on the risks and benefits of immunization and the most popular venue for receiving immunizations. Less than half of respondents who had taken their child to the physician or to a hospital, emergency department, or special clinic in the previous year reported discussing their child's immunization history with the doctor or nurse. Although this information is based on parental recall, if it is accurate then the indication is that many opportunities are missed for education about or delivery of immunization.

Validation of the parental records with other sources of records was discussed in the planning phases of the survey. By validating the results, there would be greater confidence in the representativeness of immunization coverage from parental records. Validation was not completed because of operational and confidentiality barriers, but this should be considered for any future study of immunization coverage.

Since 1996, there has been a recognized need for immunization registries to collect coverage data(7). Immunization registries may reduce the inaccuracies associated with coverage estimates obtained from parental records and provide a more robust measure of coverage in Canada. However, using a registry network to assess national coverage could have the same limitations as parental records if it is not updated and maintained for every immunization. If maintained and operated appropriately, immunization registries could provide the ideal mechanism by which to obtain timely and accurate measures of immunization coverage for all children in Canada in tandem with attitudinal surveys to measure parental awareness of immunization programs.

References

  1. Romanow RJ. Building on values: the future of health care in Canada. 2002. URL: <http://www.hc-sc.gc.ca/english/pdf/romanow/pdfs/HCC_Final_Report.pdf>.

  2. Bos E, Batson A. Using immunization coverage rates for monitoring health sector performance. Measurement and interpretations issues. World Bank HNP Discussion Papers, 2000.

  3. Health Canada. Canadian national report on immunization 1996. CCDR 1997;23(suppl S4):1-50.

  4. Canadian national report on immunization 1997. Paediatr Child Health 1998;3(suppl B).

  5. Bentsi-Enchill A, Duclos P. Vaccination coverage levels among children two years of age and selected aspects of vaccination practices in Canada. Paediatr Child Health 1997;2(5):324-28.

  6. Canadian national report on immunization 1998. Paediatr Child Health 1999;4(suppl C):23C -24C.

  7. Health Canada. Canadian national report on immunization 1996. CCDR 1997;23(suppl S4):38-39.

  8. Health Canada.. Canadian immunization guide, 6th ed. Ottawa: Health Canada, 2000. Cat. No. H49-8/2002E.

  9. Duclos P, Hatcher J. Epidemiology of influenza vaccination in Canada. Can J Public Health 1993;84(5):311-5.

  10. Duclos P. Vaccination coverage of 2-year-old children and immunization practices - Canada, 1994. Vaccine 1997;15(1):20-4.

  11. Bentsi-Enchill MB, Duclos P, Scott J et al. Childhood pertussis immunization status as reported by parents and the completeness of public-health and physician records in Nova Scotia. CCDR 1996;22(24):201-208.

Source: L McWha, A MacArthur, MHSc, T Badiani, MHSc, University of Toronto; H Schouten, RN, MHSc, T Tam, MD, FRCPC, A King, MD, FRCPC, Immunization and Respiratory Infections Division, Centre for Infectious Disease Prevention and Control, Public Health Agency of Canada, Health Canada


* This review will be appearing as a CCDR supplement in the near future.

**Members: Ms. Amy MacArthur and Ms. Tina Badiani, University of Toronto, and Immunization and Respiratory Infections Division, Health Canada; Ms. Marion Perrin, First Nations and Inuit Health Branch, Health Canada; Dr. Victor Marchessault, NACI; Ms. Lynn Cochrane, National Immunization Registry Network Working Group (NB); Ms. Rosalie Tuchscherer, National Immunization Registry Network Working Group (SK); Dr. Monika Naus, National Immunization Registry Network Working Group (BC); Dr. Bernard Choi, Evidence and Information for Chronic Disease Policy Division, Centre for Chronic Disease Prevention and Control, Health Canada; Dr. Wikke Walop, Immunization and Respiratory Infections Division, Health Canada.


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