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

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 (DTP3) using the nationally reported number of children vaccinated with DTP3 (the numerator) and the nationally reported number of children in the target population (the denominator) and compared this value with DTP3 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 DTP3 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.