The COVID-19 pandemic has highlighted the pivotal role of vaccination in reducing global morbidity and mortality, with vaccine efficacy underpinned by complex immunological mechanisms that coordinate both immediate and long-term protection. Innate immunity provides the first line of defense through pattern recognition receptors, type I interferons, and proinflammatory cytokines, while dendritic cells bridge this early response to adaptive immunity by presenting antigens to naïve T lymphocytes. This process initiates the differentiation of CD4+ helper subsets, CD8+ cytotoxic T cells, and B cells, leading to antibody production, affinity maturation, and the establishment of durable immunological memory. Complementing these mechanisms, the phenomenon of hybrid immunity—arising from the combination of natural infection and vaccination—has been shown to generate qualitatively superior protection, characterized by higher titers of cross-neutralizing antibodies, broader memory B cell repertoires, and sustained T cell activity, thereby offering enhanced resilience against emerging variants such as Delta and Omicron. At the same time, individuals with chronic respiratory diseases and allergic predispositions represent a vulnerable subgroup whose responses may be influenced by underlying inflammation, immunomodulatory therapy, or hypersensitivity to vaccine components, with rare but notable adverse events such as polyethylene glycol–related anaphylaxis and transient respiratory exacerbations underscoring the need for tailored vaccination strategies. By synthesizing current immunological insights, this review emphasizes the interplay between innate and adaptive responses, the synergistic benefits of hybrid immunity, and the clinical considerations for at-risk populations, thereby supporting the development of inclusive, adaptive, and evidence-based vaccination approaches that address the evolving challenges of SARS-CoV-2 and ensure equitable protection across diverse global settings.