Childhood National Immunization Coverage Survey (CNICS)

Detailed information for 2021

The purpose of the Childhood National Immunization Coverage Survey is to collect information on national immunization coverage for vaccines administered to children and pregnant women.

Data release - June 12, 2023 (Results for the main survey on childhood vaccination)

• Questionnaire(s) and reporting guide(s)
• Description
• Data sources and methodology
• Data accuracy

Description

The purpose of the Childhood National Immunization Coverage Survey (CNICS) is to collect information on national immunization coverage for vaccines administered to children and pregnant women. The survey is intended to:

- Determine whether children and pregnant women are vaccinated in accordance with recommended immunization schedules for publicly funded vaccines;
- Provide the World Health Organization and the Pan American Health Organization with estimates of national vaccine coverage for childhood vaccines such as those against measles, diphtheria, pertussis, tetanus and polio;
- Provide information on parental and guardian knowledge and beliefs about vaccines.

Results for the 2021 cycle of CNICS have been released in two stages: those for vaccines received during pregnancy were published in December 2022 and results for childhood vaccines have been released in the spring of 2023.

Reference period: Varies

Collection period: From winter to spring 2022

Subjects

• Children and youth
• Health

Data sources and methodology

Target population

The target population for this survey is children and youth aged 2, 7, 14 and 17 years old on March 1, 2021, and women who have given birth between September 1, 2020, and March 1, 2021, living in the 10 provinces and three territories. It excludes those residing on First Nations reserves and those living in institutions.

Instrument design

The survey content of the 2011 CNICS was developed in collaboration with the Public Health Agency of Canada. It was tested by Statistics Canada's Questionnaire Design Resource Centre (QDRC) in one-on-one interviews in participants' homes prior to collection. There were no significant content changes in 2013 and 2015. New survey content was developed in 2017 and tested by the QDRC in one-on-one interviews in testing facilities in Vancouver, Montreal and Ottawa. New survey content was also developed in 2019 when the survey moved to an electronic questionnaire and was tested by the QDRC in one-on-one interviews in Montreal and Ottawa.

For the 2021 cycle, a few questions were added to the questionnaire and were tested in one-on-one virtual interviews conducted by Statistics Canada's Centre for Social Data Integration and Development and the QDRC. The COVID-19 pandemic has highlighted the need for up-to-date data on childhood immunization coverage. A module on immunization during the COVID-19 pandemic was added to the 2021 CNICS questionnaire. In accordance with the Employment Equity Act, a population group question has been added for this cycle. This question allows to produce two main variables: the Visible minority variable and the Population group variable.

Data collection for the CNICS is composed of multiple components. For respondents with children aged 2, 7, 14 or 17 years old, the first component of the survey is an electronic questionnaire or a computer-assisted telephone interview (CATI). For this component, the person most knowledgeable (PMK) about the child's immunizations provides information about vaccines the child has received and answers questions on their knowledge and beliefs about immunization. For the second component, respondents are asked to complete and return by mail a form that provides consent for Statistics Canada to contact their child's health care provider to obtain their child's vaccine history. The receipt of the consent form triggers the third component, the Immunization Record Request form. This is a mail-out mail-back questionnaire sent to the child's health care provider, who fills out and returns the form with the child's detailed immunization history. The data from the health care provider are used to enhance the PMK-reported data.

The 2021 CNICS includes a module for women who have recently given birth. Biological mothers are asked questions about vaccines they were offered and received during their recent pregnancy, in addition to questions about their knowledge and beliefs regarding immunization. This component of the survey is conducted via an electronic questionnaire or CATI, and Statistics Canada does not contact health care providers for these respondents.

The 2021 CNICS asks respondents for permission to access their child's vaccination record from regional, provincial and territorial immunization registries. Where available, the linked data will be used to evaluate the potential to integrate immunization registry data into future cycles of the survey. To access this information, Statistics Canada must enter into data sharing and data acquisition agreements with each individual jurisdiction. Linkage will only be undertaken for consenting respondents.

Statistics Canada has data sharing and data acquisition agreements in place with Prince Edward Island and Manitoba for the 2021 survey cycle and has completed an assessment of the registry coverage for these provinces. Parents and guardians living in these two provinces will be given the opportunity to skip the detailed questions about vaccination, providing they agree to share their child's identifiers with the respective provincial immunization registry. When consent is provided, registry immunization data will be used instead of parent or guardian or health care provider data.
Women in these provinces who have recently given birth will also be asked whether they consent to Statistics Canada linking to provincial registry immunization data to assess registry coverage for this population. For the 2021 CNICS, these respondents need to respond to the detailed vaccine questions.

Sampling

This is a sample survey with a cross-sectional design.

The main objective of the 2021 CNICS is to produce national, provincial and territorial estimates of immunization coverage for women who gave birth between September 1, 2020, and March 1, 2021, and for children aged 2 years old, and national estimates of immunization coverage for children and youth aged 7, 14 and 17 years old as of March 1st, 2021. The sampling frame is stratified by age and by province or territory to ensure that the sample is representative while remaining efficient. It was determined that a sample of 19,494 units (6,781 pregnant women and 12,713 children) would yield the desired accuracy.

Data sources

Data collection for this reference period: 2022-01-10 to 2022-06-17

Responding to this survey is voluntary.

Data are collected directly from the PMK for children and youth aged 2, 7, 14 and 17 years old, and from the biological mother for children younger than 1 year old.

Data are collected using an electronic questionnaire and CATI.

With consent, data are also collected from the selected 2, 7, 14 or 17 year old child's immunization provider (e.g., physician, nurse or clinic). The data collected from the health care provider are combined with the immunization data collected from the parent or guardian.

Immunization data are also obtained from regional, provincial and territorial immunization registries when the CNICS respondent has given consent to link to and access the child's vaccination record or, in the case of women who have recently given birth, to link to and access their own vaccination record. This step happens only for jurisdictions with which Statistics Canada has concluded data sharing and data acquisition agreements.

View the Questionnaire(s) and reporting guide(s) .

Error detection

The purpose of processing survey data is to convert the collected data into a form that is appropriate for analysis and tabulation.

For the CNICS, collection was performed using a self-response electronic questionnaire (EQ) or Computer Assisted Telephone Interview (CATI), which allows for certain edits to be built into the application. For example, Validity Edits, which ensure that the response falls within the allowed range. It also ensured that only character values were entered into character fields or numeric values were entered into numeric fields.

After collection the raw data file was put through a series of standard processing steps designed to clean the data and help ensure its consistency thereby increasing its usefulness. These verifications were carried out at both at the micro and macro level.

The flow edits replicated the flow patterns used in the application and set the non-applicable questions to a value of 'Valid Skip'. Non-responses were set to a value of 'Not Stated'. These are questions that were applicable to the respondent but were not answered. When a Computer Assisted Telephone Interview (CATI) application was used for past cycles, these values were recorded as a response of 'Refusal' or 'Don't Know'.

In addition, various types of editing were done to detect missing or inconsistent information. For example, edits were performed to check the logical relationship between responses.

New variables were derived using collected data. A derived variable may be created based on a single variable (by re-grouping or collapsing categories) or based on several variables (by combining them together to define a new concept).

Imputation

Income information was not collected for this survey cycle. In order to reduce respondent burden, total household income was retrieved using linkage to tax data files. When data linkage was not possible, income was imputed using the trend imputation method or nearest-neighbour imputation method. In addition, some imputation for tetanus, diphtheria and pertussis immunization was done to account for the fact that these vaccines are only available in combination (Tdap or Tdap-IPV) in Canada.

Estimation

The Childhood National Immunization Coverage Survey (CNICS) is a probability survey. As is the case with any probability survey, the sample was selected to be able to produce estimates for a reference population. Therefore, each unit in the sample represents a certain number of units in the population.

Weighting was conducted separately for the pregnant women and children components of the sample.
Survey weights were calculated by taking the design weights and making adjustments for survey non-response. The design weight is the inverse of the probability of selection, that is, for example, the probability that a mother or a child in the population is selected into the CNICS sample.

Weights were adjusted in order that the respondents also represent the non-respondents. This ensures population totals are not underestimated. The method of response homogeneous groups (RHG) was applied to reassign the weight of the non-respondents to the respondents. The RHG method involves grouping together individuals with the same likelihood of response and then computing an adjustment factor for each RHG.

These weights are used to estimate vaccine coverage rates as well as knowledge and beliefs about vaccines for the population groups. The weights were calculated using the aforementioned methodology.

Given that exact counts of birth mothers do not exist, no post-stratification was made for the pregnant women sample. For the children's sample, post-stratification adjustments were done using projected population counts from Statistics Canada's Labour Force Survey.

To estimate variances directly, a set of 1,000 bootstrap weights is also created and made available in a separate file.

Quality evaluation

While rigorous quality assurance mechanisms are applied across all steps of the statistical process, validation and scrutiny of the data by statisticians are the ultimate quality checks prior to dissemination. Many validation measures were implemented. They included (among others):
a) Analysis of changes over time (where possible)
b) Verification of estimates through cross-tabulations
c) Consultation with stakeholders internal to Statistics Canada
d) Consultation with the Public Health Agency of Canada
e) Review of production processes
f) Coherence analysis based on quality indicators

Disclosure control

Statistics Canada is prohibited by law from releasing any data which would divulge information obtained under the Statistics Act that relates to any identifiable person, business, or organization without the prior knowledge or the consent in writing of that person, business, or organization. Various confidentiality rules are applied to all data that are released or published to prevent the publication or disclosure of any information deemed confidential. If necessary, data are suppressed to prevent direct or residual disclosure of identifiable data.

To keep the data confidential, some modifications are performed on the collected data. For example, the survey questionnaire asks for the country of origin of the child and parents; however, only the continent of origin is available in the microdata file.

Revisions and seasonal adjustment

This methodology does not apply to this survey program.

Data accuracy

As the data are based on a sample of persons, they are subject to sampling error. That is, estimates based on a sample will vary from sample to sample, and typically they will be different from the results that would have been obtained from surveying the entire population.

The quality of estimates produced with CNICS data is measured with the confidence intervals (CI), produced using bootstrap weights. The CI range will depend on the domain of interest and the prevalence of the characteristic.

The overall unweighted response rate for the pregnant women component of the survey was 51.3% at the national level. The response rate reported is calculated as the number of biological mothers who responded to questions in either the immunization or the knowledge and beliefs section of the survey, as a percentage of the number of newborns included in the initial sample, adjusted to account for out-of-scope units.

The overall unweighted response rate for the childhood vaccinations component of the 2021 CNICS was 43.9% at the national level. The response rate by age group ranged between 34.6% and 50.1% and can be found below - see additional documentation. The response rates reported here are the number of children whose parents responded to questions in either the immunization or the knowledge, attitudes and beliefs section of the survey as a percentage of the number of children included in the initial sample, adjusted to account for out-of-scope units.

In other words, for both components of the survey the response rates are calculated as:
Response rate = (number of respondents / effective sample size) * 100%

Much time and effort were devoted to reducing non-sampling errors in the survey by using a well-tested questionnaire, a proven survey methodology, specialized interviewers and quality control measures.