The procedures employed at the two survey waves related to sampling and data collectionwere very similar and are described in detail elsewhere [17]. In brief, participants were selected based on two-stage complex sampling procedures. In the first stage, considering the number of children immunized in each center, random drawing of the immunization center within the capital immunization centers were selected; in the second stage, infants waiting to be vaccinated were also systematic randomly selected. Mothers were interviewed using a standard questionnaire with closed ended questions. Data were collected on socio-economic and demographic infant, maternal and household characteristics, pacifier use, and consumption of breast milk and other foods by the infant in the previous 24 hours.