Impact of vaccine stockouts on immunization coverage in Nigeria.

Improving immunization coverage requires creating reliable supply of vaccines and immunization supplies; trained and incentivized health workers; and strategies to improve the demand for immunization. Yet, the interplay of demand and supply side factors on immunization coverage has not been evaluated in literature with data. We use data from Nigeria and a mixed-effects general linear model to estimate the effect of vaccine availability on routine immunization coverage and to identify demand and health system factors which affect this relationship. We find that when vaccine stockouts occur at Local Government Area stores in Nigeria, they significantly decrease the number of children immunized, and for most vaccines, the effect lasts for several months after a stockout. Some of the demand lost when a stockout occurs is recovered over the following six months as children catch up with the regimen. The magnitude of the impact varies across different vaccines.