Knowledge, perceptions, and adherence to vaccination schedules among Brazilian adults: an online cross-sectional survey

Abstract

Introduction: Despite the historical advances of the National Immunization Program (PNI), adherence to the adult vaccination schedule in Brazil remains insufficient, contributing to increased vulnerability to vaccine-preventable diseases.

Objective: To analyze the level of knowledge, perceptions, and vaccination habits of Brazilian adults, identifying barriers and potential strategies to strengthen lifelong immunization.

Methods: An observational, descriptive, cross-sectional study conducted through an electronic questionnaire consisting of 16 multiple-choice questions, disseminated via social media between June 10 and June 19, 2025. Adults (≥18 years), residing in Brazil and active users of social media, were included.

Results: The sample comprised 139 participants, predominantly women (69.1%), with a high level of education (89.9% with university degrees). While 90.6% had completed the childhood vaccination schedule, only 43.9% reported keeping their vaccinations up to date in adulthood. Regarding knowledge, 68.3% reported doubts or lack of awareness about the adult vaccination schedule, and only 27.3% stated they were well informed. Full confidence in vaccines was reported by 77.7% of respondents, whereas 20.9% expressed doubts and 1.4% reported distrust. Among healthcare professionals (n = 53), 13.2% reported uncertainties regarding vaccine safety and efficacy.

Conclusion: The findings highlight significant gaps in adult immunization continuity in Brazil, including among highly educated individuals and healthcare professionals. Clear communication strategies, continuing education, and the use of social media as a tool for disseminating reliable information may help improve adherence to the adult vaccination schedule.