Reply to comments on Monitoring vaccination coverage: Defining the role of surveys.

Dear Editor,

We thank Pond and Mounier-Jack for their comments on our

paper, ‘‘Monitoring vaccination coverage: Defining the role of

surveys” [1]. We agree that for many countries, administrative

estimates of coverage are greatly inflated and misleading for programme

planning purposes. The robustness of the WHO-UNICEF

estimates of national immunization coverage (WUENIC) depends

on the quality of the underlying data reviewed, which include

administrative reports, as well as probability and non-probability

sample surveys. In 2012, the Grade of Confidence (GoC) was introduced

as a means of conveying uncertainty in WUENIC [2] and is

low in the seven conflict-affected countries listed by Pond and

Mounier-Jack. Table 1 shows that in five of these countries,

vaccination cards were available for less than half the children surveyed;

when card availability is low, it is particularly difficult to

compare coverage trends. For example, in Nigeria, the proportion

of children with DTP3 according to card was similar in surveys in

2010, 2011 and 2013, but in the EPI survey of 2010 a verbal history

of vaccination was reported for 43% of children, more than double

that of previous or subsequent surveys. Elsewhere, results from

surveys did not always match expected trends (e.g. no apparent

fall in coverage between surveys despite a 7 month stockout of

DTP in one country), and some results were very unlikely (e.g. zero

dropout between DTP1 and DTP3 in one Multiple Indicator Cluster

Survey (MICS) (data from country reports at http://apps.who.int/

immunization_monitoring/globalsummary/wucoveragecountrylist.

html)).

The updated WHO guidelines on vaccination coverage surveys

(http://www.who.int/immunization/monitoring_surveillance/

Vaccination_coverage_cluster_survey_with_annexes.pdf) discuss the challenges of using a new survey to compare with an older

one, particularly an immunization coverage survey – these often

lacked information on likely biases and confidence intervals were

either not reported or not very meaningful from non-probability

samples. The best way to compare results from different surveys

is to plan a pair of surveys for such a purpose and work very hard

to ensure standardised, well-documented and high quality data

collection in both. Pond and Mounier-Jack suggest that two such

surveys are feasible within each 5 years period. We would be

reluctant to stipulate any particular interval as the usefulness of

repeat surveys will depend in part on the likelihood of a change

in coverage having occurred (which can be predicted from

monitoring other indicators) [1] and the availability of accurate

documentation of vaccination status on home-based or clinic

records. Most of all, surveys should lead to action to strengthen

programme performance and this is likely the weakest link in

many countries, including those affected by conflict.