Vaccination Barriers in Brazil: Exploring Hesitancy, Access, and Missed Opportunities in a Cohort of Children (2017–2018)—National Vaccination Coverage Survey Results (2020–2021)

Background/Objectives: In recent years, Brazil has experienced declining vaccination coverage, raising concerns about vaccine hesitancy and barriers to access. This research analyzes the reasons for non-vaccination among children born in 2017 and 2018 in a metropolitan area of the state of São Paulo in 2020 and 2021. Methods: Data were obtained from a retrospective cohort of children born in 2017 and 2018, living in Campinas, monitored during the first 24 months by vaccination records. A stratified and clustered sample by census sector was performed according to socioeconomic conditions. The reasons for non-vaccination were obtained from interviews with the children’s guardians. Results: A total of 1775 caregivers were interviewed, and 63.1% of children had complete vaccination coverage, with lower socioeconomic groups presenting the highest rates for non-vaccination. The study identified three main groups for non-vaccination: vaccine hesitancy (e.g., fear of side effects, misinformation) in 1.7% of respondents, access difficulties (e.g., service location, financial constraints) in 7.9%, and missed opportunities (e.g., lack of vaccines, administrative barriers) in 16.4%. Conclusions: The findings indicate that the main reported barriers to childhood vaccination are missed opportunities in healthcare services, often due to vaccine shortages or administrative issues, along with social vulnerabilities. Vaccine hesitancy stems from misinformation and fear of side effects. Despite these challenges, families persist in seeking vaccination. However, coverage remains below the national targets, particularly in the second year of life. Targeted public health interventions are urgently needed to improve vaccine confidence, accessibility, and healthcare system efficiency.