Validity of maternal recall for estimating childhood vaccination coverage - Evidence from Nigeria

Vaccination coverage surveys in low- and middle-income countries typically estimate vaccination coverage using data from vaccination cards, parental recall, or a combination of the two. However, these surveys are often complicated by the pervasive absence of vaccination cards, forcing researchers to rely on parental recall. We assessed the validity of mothers' recall against home-based vaccination cards using data from a community-based household survey in Nigeria.

A cross-sectional survey of 1,254 mothers of children aged 12-23 months was performed in Enugu State, Nigeria in July 2020. Data on vaccination status for BCG, OPV, DPT, Measles, Yellow fever, and Vitamin A supplement were collected using two data sources: home-based vaccination cards and mothers' recall. We evaluated the level of agreement between the two data sources; estimated the sensitivity and specificity of mothers' recalls; and computed multivariable regression models to identify socio-demographic factors associated with mothers' recall bias.

Out of 1,254 mothers interviewed, 578 (46.1%) mothers with vaccination cards were included in this analysis. Vaccination coverage levels were generally similar across data sources, though recall-based data generally underestimated the coverage. The level of agreement between the two data sources was high (≥91.0% for all vaccine types) with recall bias due to under-reporting generally higher than recall bias due to over-reporting. The sensitivity of parental recalls was high for all vaccine types, while the specificity was low across vaccine types. Across all vaccines, mothers recall bias was significantly associated with the rural residence and not receiving postnatal care.

In the absence of vaccination cards, mothers' recall of their children' vaccination status for BCG, OPV, DPT, Measles, Yellow fever and Vitamin A is a valid instrument for estimating childhood vaccination coverage in this setting in Nigeria. However, additional research is needed to confirm these findings at higher sub-national and national levels.