A Comparison of National Immunization Programme Target Population Estimates with Data from an Independent Source and Differences in Computed Coverage Levels for the Third Dose of DTP Containing Vaccine

Abstract

Background: Comparison of target populations for immunization used by national immunization programmes with independent sources can be useful for identifying irregular patterns. Similarly, understanding differences in computed coverage levels that result from changes in target population estimates can be important. Methods: Using data reported annually by national immunization programmes to WHO and UNICEF, we compared the national number of births and surviving infants with estimates reported by the United Nations Population Division (UNPD). We also re-computed and compared coverage levels for the third dose of DTP containing vaccine (DTP 3 ) using the nationally reported number of children vaccinated with DTP 3 (the numerator) and the nationally reported number of children in the target population (the denominator) and compared this value with DTP 3 coverage computed using the nationally reported number of children vaccinated and the UNPD estimate of the national number of surviving infants as an independent denominator. Results: We observed differences in the number of births and surviving infants reported by national immunization programmes compared with those estimated by the UNPD. Year-to-year changes in the number of births and surviving infants reported by national immunization programmes often exceeded those estimated by the UNPD. The re-computed administrative coverage levels for DTP 3 using a nationally reported target population tended to be higher on average than those re-computed using the UNPD target population estimates. Conclusion: Target population estimates are a challenge for immunization programmes, and comparison to independent sources can be useful. There is increasing need to trace and better understand the processes and conditions affecting the enumeration and recording of the number of children in the target population for immunization services and the number of children vaccinated while recognizing that the challenge to do so is greater in some locations than others.

Assessing the quality and accuracy of national immunization program reported target population estimates from 2000 to 2016

“…WHO Member States that use the administrative method to estimate vaccination coverage have been reporting national-level immunization coverage data for recommended vaccines to the WHO/UNICEF JRF since 1998 [5]. The JRF currently collects data on administered doses (the numerator in coverage estimates) and national target populations for each scheduled antigen (the denominator in coverage estimates) [5].…”

“…The JRF currently collects data on administered doses (the numerator in coverage estimates) and national target populations for each scheduled antigen (the denominator in coverage estimates) [5]. Countries that recommend the BCG vaccine typically do so at birth, so the target population is LB [3].…”

“…This list was selected because it includes elements related to data quality, such as completeness of reporting (1 and 2), unlikely (3 and 4) and implausible values (5 and 6), and external inconsistencies (7 and 8) [3,5]. Also, these elements have been already used to assess denominators used for immunization [3,5].…”

“…Studies comparing the United Nations Population Division (UNPD) projections of LB and SI to administrative estimates have suggested a tendency for administrative target populations to be lower than UNPD estimates [4]. Another study found that coverage levels of a third dose of a diphtheria-tetanus-pertussis containing vaccine (DTP3) were higher when calculated using JRF target populations as the denominator compared to coverage estimates re-calculated using UNPD target population estimates [5]. …”

Trends in differences between births and surviving infants reported for immunization program planning and external data sources in Eastern and Southern Africa 2000–2013

“…Because of concerns of frequently observed administrative coverage rates over 100%, e.g., when measles or polio district coverage rates are needed for outbreak risk assessments, and to inform our support for immunization programs in WHO Member States in Eastern and Southern Africa, we compared annual trends in target populations reported by Member States through the WHO-UNICEF joint reporting form (JRF) [2] with United Nations (UN) population projections and modeled infant mortality estimates. Inconsistencies between JRF and external source data have been reported in the literature, indicating the need to better understand the processes and conditions affecting target populations estimates used in national EPI programmes [3][4][5]. The objective of our analysis was to determine differences in trends of JRF and external data sources, identify possible reasons for overestimating immunization coverage and discuss strategies for improvement in the Member States that our team supports.…”