Childhood National Immunization Coverage Survey (CNICS)

Detailed information for 2019

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.

Data release - November 10, 2020 (Results for vaccines administered during pregnancy); May 3, 2021 (Results for 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 if children are vaccinated in accordance with recommended immunization schedules for publicly-funded vaccines
- Determine if pregnant women are being vaccinated against pertussis (whooping cough) and the flu, vaccines recommended during pregnancy
- Provide the World Health Organization and the Pan-American Health Organization with estimates of national vaccine coverage for childhood vaccines such as measles, diphtheria, pertussis, tetanus and polio
- Provide information on parental and guardian knowledge and beliefs about vaccines.

Results for the 2019 cycle of CNICS was released in two stages, with those for vaccines received during pregnancy published in November 2020 (this component is also referred to as the Survey of Vaccination during Pregnancy) and results for childhood vaccines released in April 2021.

Reference period: Varies

Collection period: December 2019 to August 2020

Subjects

• Children and youth
• Health

Data sources and methodology

Target population

The target population for the 2019 cycle of this survey is children aged 2, 7, 14 and 17 years old on March 1, 2019, and women who have given birth between September 2, 2018 and March 1, 2019, living in the 10 provinces and three territories, not residing on First Nations reserves, not in foster care and not institutionalized.

Instrument design

The survey content of the original CNICS in 2011 was developed in collaboration with the Public Health Agency of Canada (PHAC). The survey content was tested by the Questionnaire Design Research Centre (QDRC) of Statistics Canada during 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 added for CNICS 2019 and tested by the QDRC through one-on-one interviews in Montreal and Ottawa.

For respondents with children aged 2, 7, 14 and 17 years old, data collection included multiple phases. The first phase of collection was conducted through a self-response electronic questionnaire (EQ) or a computer assisted telephone interview (CATI) during which the person most knowledgeable about the child's immunizations (PMK), provided information about vaccines the child had received and answered questions regarding their knowledge and beliefs about immunization. In the second phase of collection, respondents were asked to complete and return by mail a form which provides consent for Statistics Canada to contact their child's immunization providers to obtain their child's vaccine history. The receipt of the consent form, triggered the third phase, the Immunization Record Request form, a mail out/mail back questionnaire sent to the child's health care provider(s) who filled out and returned the form with the child's detailed immunization history. The data from the health care providers were used to enhance the PMK reported data.

For the first time, in 2019, the CNICS included a component on prenatal vaccination, also known as the Survey of Vaccination during Pregnancy. For this component of the survey, biological mothers were asked questions about vaccines they were offered and received during their recent pregnancy, in addition to questions about their knowledge and beliefs regarding immunization. Data on vaccines received during pregnancy were collected via a self-response electronic questionnaire (EQ) or a computer assisted telephone interview (CATI), and Statistics Canada did not contact immunization providers for these respondents.

The 2019 CNICS asked respondents for permission to access their child's vaccination record or, for pregnant women, their own vaccination record held by regional, provincial and territorial immunization registries. Where available, and where permission has been given, the linked data will be used to evaluate the potential to further integrate immunization registry data in future cycles of the survey. In order to access this information, Statistics Canada must have data sharing agreements and data acquisition agreements in place with each individual jurisdiction.

To this date, Statistics Canada has completed an assessment of the registry coverage for Prince Edward Island and Manitoba (after having put in place data sharing and data acquisition agreements) for childhood vaccination. As a result, parents and guardians living in these two provinces were given the opportunity to skip the detailed questions about vaccination, providing they agreed to share their child's identifiers with the respective provincial immunization registry. When consent was provided, registry immunization data was used in the place of parent or immunization provider data. Women in these provinces who had recently given birth were also asked whether they consented to Statistics Canada linking to provincial registry immunization data in order to assess registry coverage for this population. For the CNICS 2019, these respondents were asked to respond to the detailed vaccine questions.

Sampling

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

The main objectives of the 2019 CNICS are to 1) produce national, provincial and territorial estimates of immunization coverage for women who have given birth between September 2, 2018 and March 1, 2019 and 2) national estimates of immunization coverage for children and youth aged 2, 7, 14 and 17 years old. The target population is stratified by age and by province and territory to ensure that the sample is representative while remaining efficient. It was determined that a sample of 9,096 units for pregnant women, and 4,830 units for the children portion would yield the desired accuracy.

Data sources

Data collection for this reference period: 2019-12-02 to 2020-08-31

Responding to this survey is voluntary.

Data are collected directly from the Person Most Knowledgeable (PMK) for children aged 2, 7, 14 and 17 years old, and from the biological mother for children under 6 months of age, as of March 1, 2019.

Data are collected using a self-response electronic questionnaire (EQ) and a computer-assisted telephone interviewing (CATI).

With consent, data are also collected from the selected child's immunization provider (e.g. physician, nurse, or clinic). The data collected from the immunization provider is combined with the immunization data collected from the parent or guardian.

Immunization data is also obtained from the regional, provincial and territorial immunization registries when the CNICS respondent has given consent to link to and access the child's vaccination record. This step only happens for jurisdictions with whom Statistics Canada has concluded data sharing and data acquisition agreements. For this cycle, Statistics Canada has agreements with Manitoba and Prince Edward Island.

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 so as 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.

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 population counts from Statistics Canada's Labour Force Survey.

For the 2019 cycle, in contrast to past cycles of the survey, only one set of weights are calculated for each of the samples (children and mothers) included for CNICS. 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.

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 information it collects which could identify any person, business, or organization, unless consent has been given by the respondent or as permitted by the Statistics Act. 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.

In order to keep the data confidential, some modifications are performed on the collected data.

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 58.9% at the national level - see additional documentation. 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 2019 CNICS was 54.5% at the national level. The response rate by age group ranged between 43.9% and 60.0% 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 was 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.

• Additional documentation