Background/Objectives: Vaccination represents a significant achievement of public health and should be regarded not only as a protective measure against infectious diseases but also an active preventive intervention and a component of health promotion. Methods: This cross-sectional study assessed vaccination coverage among adults aged ≥60 years who attended a Primary Health Care Center during a predefined period of at least two months (November–December 2025) in a rural area of Crete, Greece, and examined determinants of immunization, including demographic, clinical, psychosocial, and health service utilization factors. The sample comprised 366 participants who consented to complete a structured questionnaire, primarily via interview, followed by verification of vaccination status through medical records. Results: High vaccination coverage was observed for influenza (82.5%), moderate coverage for pneumococcal (68.3%) and herpes zoster (56.0%) vaccines, and very low coverage for tetanus–diphtheria–pertussis booster doses (≈13%) and RSV vaccination (5.2%). For SARS-CoV-2, 96.2% received the three doses which were mandatory during the pandemic years. The overall Vaccination Coverage Score (VCS) averaged 43.1/100, while only 10.1% of participants achieved high coverage. Regression analysis showed that higher educational level, multimorbidity, and extensive use of health services were independently associated with better vaccination coverage (p < 0.05). Conclusions: The findings reveal fragmented vaccination patterns and underscore the need for systematic assessment of adult vaccination status within routine Primary Health Care. Targeted counseling, promotion of health literacy, and preventive vaccination strategies are expected to reduce vaccine-preventable morbidity and support healthy aging.