Back to the basics
Denominator issues for immunization coverage
David Brown (UNICEF)
On behalf of the WHO and UNICEF working group for
monitoring immunization coverage (T Burton and M Gacic-Dobo, WHO; R Karimov, UNICEF)
Financial discloser / conflicts of interest
None to declare.
WHO and UNICEF estimates of immunization coverage with three doses of
DTP containing vaccine (DTP3) and estimated number of children
unimmunized with DTP3 by UNICEF region during 1980 – 2010
Source: WHO and UNICEF estimates of national immunization coverage, 2011 revision (July 2012)
Note: Circle size proportional to estimated number of children unimmunized with DTP3 based on population estimates from the
United Nations, Department of Economic and Social Affairs, Population Division (2011). World Population Prospects: The
2010 Revision, CD-ROM Edition.
Hypothetical example
National coverage level = 86%; 5 of 15 districts with coverage >99%
Coverage
number of children in the target population who are vaccinated
number of children in the target population
Target Populations
 planning services, managing stocks and supplies and
targeting interventions
 ideally would use complete vital registration
 not available in majority of low- and middle-income countries
 managers must estimate the number of children in the target
population (e.g., surviving infants) based on counts or
estimates by local programme staff or health workers or rely
on population projections from the latest census data
 changing fertility, mortality and/or migratory patterns over
time create further challenges
 how often do we get it “right”?
 steps to assess plausibility of information set
WHO Manual for Improving Target Population
Estimates for Immunization
 WHO has developed a manual to provide relevant
knowledge and practical guidance for national immunization
programs that aim to improve the accuracy of their
denominator estimates and the quality of their system for
producing coverage estimates
 Includes a series of objective quality tests on existing
denominator data, both internal and external checks, and
suggests how to use the results of these tests, how to
analyze apparent deficiencies in the data, and how to work
toward more accurate denominators when the analysis
indicates inaccurate denominators
WHO Manual for Improving Target Population
Estimates for Immunization
 Missing data checks
 Internal checks
 Equality of non-BCG denominators
 Implausible growth rates
 External checks

Consideration of new sources of target population estimates
 Fixed factors can create problems
 Civil registration
 Population projections from census counts
 Programme specific estimates
Target Population Assessment (National)
 Compare with independent data sources
 Look at time series
Example
 comparison of estimated number of live births
and surviving infants for the years 2000 –
2010 received by WHO/UNICEF with UNPD
 comparison of implied IMR to estimated IMR
from the United Nations IGME and UNPD
Target Population Assessment Observation
Exercise
 some countries report only the number of
births
 some countries report an estimate of the
number of live births that is less than the
number of surviving infants
 where data were available the implied IMR
value differed from IGME estimates by
>25%-points in 58% of reporting events
Burkina Faso
DR Congo
Kenya
Lao People’s Democratic Republic
Vaccination cards / home-based health records

provide a systematized way of recording the
vaccines received by children as
recommended by national / international
health authorities

point-of-care information resource
 enhance health professionals’ ability to
make clinical decisions and prevent
unnecessary repetition of vaccination
 empower parents/caregivers in the
health care of their children, and
 support public health monitoring

reliance on cards as a source of
immunization data will almost certainly
underestimate coverage until the proportion
of cardholders is more nearly equal the
proportion of children immunized
Vaccination card prevalence
 Review of DHS and MICS data for 87 countries since 2000
median prevalence of cardholders 72% (min: 8%; max: 99; IQR: 59-82%)
 Cardholder prevalence < 50% in 17 of the 87 countries (20%)
50-69% in 20 countries (23%)
70-79% in 25 countries (29%)
80-89% in 13 countries (15%)
>90% in 12 countries (14%)
 Cardholder prevalence < 70% in 21 of 33 least developed
countries (according to World Bank classification)
(median: 62%; min: 8%; max: 93%; IQR: 48-74%)
Thank you!