Comparative estimates of immunisation coverage from three different sources: results from the SM2015 evaluation

Abstract Background Estimating vaccination coverage is challenging in resource-poor settings where accurate records are sparse. Household surveys, a key source of coverage information, typically capture data from child health cards and rely on maternal recall when cards are unavailable. As a result, little is known about how coverage estimates based on maternal recall differ from those based on health cards for the same children. Furthermore, little is known about how these measures compare with actual rates of seroconversion, which could be used to estimate effective coverage of immunisations. This study compares the accuracy of maternal recall, health card documentation, and antibody presence in vaccination coverage estimates in the state of Chiapas, Mexico. Methods Data for this study were collected as part of the Mesoamerican Health Initiative 2015 baseline survey. A random sample of 4700 households with children under-5 and women of reproductive age were surveyed. A pre-survey census was carried out within segments that had been randomly selected with probability proportional to size. Standardised multilingual household surveys were implemented using netbooks. Anthropometric measurements were collected for all children under-5 and dry blood spot samples for the detection of measles antibodies were collected from children aged 12–23 months. Findings Preliminary results suggest that maternal recall, child health cards, and antibody tests generate differing estimates of immunisation coverage. Recall differs from card-based estimates of vaccination coverage by up to 40 percentage points. There are potentially considerable differences in measles immunisation coverage as assessed by the presence of measles antibodies versus other survey sources, highlighting weaknesses in card accuracy, card coverage, and vaccine administration. Interpretation Current national estimates of immunisation coverage based on the combination of maternal recall and children's health cards may be overestimating actual protection against vaccine-preventable diseases. Correcting for biases in recall and card coverage may produce more accurate estimates of intervention coverage. Funding Salud Mesoamerica 2015 is funded by the Bill & Melinda Gates Foundation, the Carlos Slim Health Institute, and the Government of Spain and is administered by the Inter-American Development Bank. The content is solely the responsibility of the authors and does not necessarily represent the official views of the funders or the Inter-American Development Bank.