Data on immunization coverage often varies significantly depending on the source, which can make it a challenge to know which areas to target with strengthened immunization services. To determine vaccination coverage in three regions in Ethiopia, this study coupled serosurveys, which objectively estimate the prevalence of protected children, with immunization coverage surveys (based on vaccination cards, parental recall, and health facility registers) to measure the proportion of children protected against tetanus and Hib. In addition to showing the utility of biomarker serosurveys to monitor vaccine coverage and the insights revealed with they are done concurrently with coverage surveys, this study also was one of the first to conduct a serosurvey in a pediatric population that received the DTP vaccine bundled within the pentavalent vaccine.