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WHO and UNICEF National Immunization Coverage Estimates Summary

Core Content

The document outlines the methodology and data sources used by the World Health Organization (WHO) and United Nations Children's Fund (UNICEF) to estimate national immunization coverage. These estimates are based on a combination of administrative, official, survey, and other data sources, with adjustments made when data is incomplete or unreliable. The estimates are country-specific and reflect the most likely coverage levels, taking into account potential biases and the context of the country's immunization program.

Key Information

• Estimates are not based on ad hoc adjustments but rather on empirical data, independent recalculations, and survey evidence when available.
• Interpolation is used to estimate coverage for missing years when no direct data is available.
• Grade of Confidence (GoC) is introduced in the 2011 revision to indicate the level of empirical support for the estimates. It is not a measure of data quality but rather the strength of the supporting evidence.
• Estimate types include:
  • Administrative coverage: Based on data reported by national authorities.
  • Official coverage: Reflects national authorities' best judgment using a combination of data sources.
  • Survey coverage: Derived from population-based household surveys of children aged 12–23 or 24–35 months.

Abbreviations and Vaccine Coverage Definitions

Data Sources and Estimation Process

• Administrative data: Reported by national authorities, based on aggregated vaccination records.
• Survey data: Population-based household surveys among children aged 12–23 or 24–35 months.
• Official data: National authorities' estimates that may incorporate multiple data sources.
• Interpolation: Used when no data is available for a specific country/vaccine/year combination.
• Calibration: Data is adjusted to align with known coverage levels from previous years when necessary.

Grade of Confidence (GoC) Overview

• R+: Supported by reported data.
• D+: Supported by recalculated denominator from World Population Prospects.
• S+: Supported by at least one survey within 2 years.
• R-, D-, S-: Data sources that challenge the estimate.
• No GoC: No directly supporting data or data that challenges the estimate.

Summary of Coverage Estimates (2010–2021)

WSM - DTP1

WSM - DTP3

Notes on Data Challenges

• Small birth cohorts are frequently cited as a reason for data fluctuations.
• Public concerns and vaccine hesitancy (e.g., following deaths related to MMR vaccine) have impacted coverage in some years.
• Catch-up doses during outbreaks or campaigns have influenced reported coverage.
• Survey bias (e.g., recall bias) has been accounted for in some cases.
• Data calibration to known levels is used when direct data is lacking.

Disclaimer

All data and estimates are subject to interpretation and use. WHO and UNICEF take reasonable precautions to verify information, but they cannot guarantee accuracy. Estimates should be used with caution and assessed based on their intended purpose.