Background: Declining vaccination coverage (VC) and vaccine hesitancy among medical students are global challenges. These challenges reflect individual and logistical barriers to a sufficient adherence toward essential vaccines for healthcare professionals, as well as presenting a need for educational strategies during undergraduate training. Methods: This is a prospective study for evaluating VC rates, sociodemographic associations, and the vaccine confidence among medical students at a federal university in Brazil. The data collection included questionnaires and individual analyses of the participants’ vaccination records. Results: A total of 237 medical students from all six years of an undergraduate program participated, of whom 124 (52.3%) had a vaccination record. Although the majority considered the vaccines to be “Completely Safe” (86.9%), the VC rates for complete vaccination schedules were relatively low, ranging from 87.9% (hepatitis B vaccine) to 3.2% (meningococcal B vaccine), including the vaccines from the National Immunization Program (NIP) and the private sector. Higher VC rates were found to occur among students in the final years of their undergraduate studies, in those from families with higher monthly incomes, and those from private secondary schools. Conclusions: Given the low VC rates among medical students, other factors in addition to vaccine confidence may be determinants, thus highlighting the importance of reviewing policies for the inclusion of priority groups in the NIP and in implementing educational interventions during undergraduate training.

Objectives: To evaluate determinants of vaccine hesitancy among medical students at a Brazilian federal university using the 5C model as a theoretical framework. Methods: A cross-sectional observational study was conducted among medical students at the Federal University of Rio Grande do Sul, Brazil, between December 2024 and March 2025. Data were collected using a self-administered questionnaire conceptually based on the 5C model (confidence, complacency, convenience, communication, and context). The questionnaire was pilot-tested among medical students before application to assess clarity and comprehensibility. Sociodemographic variables and vaccine-related perceptions were analyzed descriptively and inferentially using Pearson’s chi-square, Fisher’s exact, Student’s t, and Mann–Whitney tests. Statistical significance was set at p < 0.05. Results: Out of 809 eligible students, 230 participated in the study (response rate: 28.4%). Most participants reported complete confidence in vaccines (83.5%). Complete confidence in vaccines was more frequently reported among female students than male students (89.4% vs. 75.5%; p = 0.006) and among students from private schools compared with those from public schools (87.7% vs. 78.7%; p = 0.04). Although most participants perceived moderate or high risk for vaccine-preventable diseases, 28.8% reported low risk perception. Higher perceived risk was significantly associated with higher vaccine confidence (p = 0.010). Regarding convenience, 54.0% of participants reported moderate to very high impact of logistical barriers on vaccination decisions. Healthcare professionals (32.3%) and scientific or academic sources (30.1%) were the most frequently reported information sources, although 19.9% identified social media as their primary source. Sociocultural influences on vaccination decisions were considered low or absent by most participants (66.9%). Conclusions: Medical students demonstrated high confidence in vaccines; however, determinants potentially associated with vaccine hesitancy were identified, particularly within the domains of complacency, convenience, and communication. These findings highlight the need for institutional and educational strategies to improve vaccine access, strengthen immunization education, and promote critical appraisal of health information during medical training.