Factors Associated with Vaccination Delay and Refusal Among Children Under 12 Months of Age

Background: Delayed and refused vaccination remain challenges to timely immunization during infancy and may involve different underlying factors. Objective: To analyze the factors associated with vaccination delay and refusal among children younger than 12 months. Methods: A household-based analytical cross-sectional study was conducted with 452 children in Teresina, Piauí, Brazil. Data were obtained through caregiver interviews and review of vaccination booklets. Vaccination delay and refusal were analyzed separately using Poisson regression with robust variance. Results: Vaccination delay occurred in 30.8% of children and was associated with age 7 to <12 months (aPR = 4.71), contraindication in cases of mild illness (aPR = 1.64), the caregiver’s decision not to vaccinate the child by the scheduled date (aPR = 1.79), and vaccine shortages (aPR = 1.84); satisfactory caregiver knowledge was inversely associated with delay (aPR = 0.58). Vaccination refusal occurred in 5.5% and was associated with age 7 to <12 months (aPR = 2.25), contraindication because of a previous reaction (aPR = 6.22), having considered no longer vaccinating the child after a previous reaction (aPR = 3.19), the caregiver’s decision not to vaccinate the child by the scheduled date (aPR = 3.08), and vaccine shortages (aPR = 2.31). Moderate and satisfactory knowledge were inversely associated with refusal (aPR = 0.32 and 0.13, respectively). Conclusions: Vaccination delay was more frequent than vaccination refusal. The outcomes shared some associated factors but also showed outcome-specific factors, supporting distinct approaches to improve vaccination timeliness and address refusal.