2023-07-16-世界卫生组织-Immunization_South_Africa_2023_country_profile_20页_422kb

WHO and UNICEF National Immunization Coverage Estimates Summary

Core Content

WHO and UNICEF jointly estimate national immunization coverage levels based on data submitted by Member States. These estimates aim to provide a more accurate reflection of immunization system performance by considering multiple data sources, including administrative reports, official assessments, and survey data. The estimates are not based on ad hoc adjustments but rather on a systematic review of available data, with attention to potential biases and inconsistencies.

Key Information

Vaccine-Specific Coverage Definitions

• BCG: Percentage of births who received one dose of Bacillus Calmette Guerin vaccine.
• DTP1/DTP3: Percentage of surviving infants who received the 1st or 3rd dose of diphtheria and tetanus toxoid with pertussis (DTP) vaccine.
• Pol3: Percentage of surviving infants who received the 3rd dose of polio-containing vaccine (either oral or inactivated).
• IPV1: Percentage of surviving infants who received at least one dose of inactivated polio vaccine (IPV). In countries using only IPV, it reflects the 1st dose. In sequential schedules, it reflects the 1st routine dose of IPV.
• MCV1/MCV2: Percentage of children who received the 1st or 2nd dose of measles-containing vaccine (MCV), based on the nationally recommended schedule.
• RCV1: Percentage of surviving infants who received the 1st dose of rubella-containing vaccine. Based on the first measles-rubella combination vaccine.
• HepBB: Percentage of births who received a dose of hepatitis B vaccine within 24 hours of delivery. Only available for countries with a universal birth dose policy.
• HepB3: Percentage of surviving infants who received the 3rd dose of hepatitis B vaccine.
• Hib3: Percentage of surviving infants who received the 3rd dose of Haemophilus influenzae type b (Hib) vaccine.
• RotaC: Percentage of surviving infants who received the final recommended dose of rotavirus vaccine, which may be the 2nd or 3rd dose depending on the vaccine.
• PcV3: Percentage of surviving infants who received the 3rd dose of pneumococcal conjugate vaccine (PcV), reflecting coverage with at least two doses before 1 year of age in some countries.
• YFV: Percentage of surviving infants who received one dose of yellow fever vaccine in countries where it is part of the national immunization schedule or recommended in at-risk areas.

Estimation Methods

• Administrative Coverage: Based on aggregated reports from health providers, potentially biased due to inaccurate numerator or denominator data.
• Official Coverage: Estimated by national authorities using a combination of administrative, survey, or other data sources.
• Survey Coverage: Based on population-based household surveys of children aged 12–23 or 24–35 months, considering vaccination history or caregiver recall.

WHO and UNICEF use a Grade of Confidence (GoC) to indicate the reliability of their estimates. The GoC is not a measure of data quality but of the empirical support for the estimate. It is based on:

• R+: Supported by reported data.
• D+: Supported by an independent denominator from the World Population Prospects.
• S+: Supported by at least one survey within 2 years.
• R-, D-, S-: Data sources that challenge the estimate.

Estimates are derived from:

• Directly reported data.
• Interpolation between years when data are missing.
• Survey data, adjusted for recall bias in some cases.
• Calibration of reported data with historical or future population estimates.

Data Quality and Challenges

• 2011–2013: Coverage estimates were calibrated using historical data (e.g., 2003, 2005, 2010) due to inconsistencies in reported data.
• 2014–2016: Survey data were used to adjust reported data for recall bias, but inconsistencies and unexplained declines in target population data were noted.
• 2017–2022: Estimates are based on reported data, but the private sector's contribution is not fully captured. Some years show vaccine stockouts affecting coverage.

Summary Table of Coverage Estimates

Notes on Estimation Challenges

• 2014–2016: Some estimates were adjusted using survey data and recalculated denominators.
• 2017–2022: Estimation based on reported data, but may not fully reflect private sector contributions.
• 2016: Data inconsistent with previous and subsequent years, leading to interpolation.
• 2015–2014: Unexplained declines in target population data, suggesting possible data inaccuracies or changes in reporting practices.
• 2013–2011: Data calibrated to historical estimates due to inconsistencies.

Disclaimer

WHO and UNICEF emphasize that all estimates are based on varying data quality and should be used with caution. They are not accompanied by classical uncertainty measures such as confidence intervals, and the GoC is not a judgment on the quality of data but on the empirical support for the estimate. Users are encouraged to interpret these estimates in the context of their intended use and to consider potential biases and data limitations.