Vaccination continues to be one of the most successful public health measures; however, the traditional vaccine platforms face constant hurdles, such as the efficacy of vaccines being variable in different populations, poor mucosal immunity, the need for cold chain storage, and reduced immunogenicity in the setting of immune compromise or microbiome dysbiosis. Over the past decade, there has been an increasing body of evidence that has revealed the human microbiota to be a critical regulator of innate and adaptive immunity, significantly influencing susceptibility to infection and vaccine response. This chapter explores the concept of microbiota-based vaccine alternatives as a revolutionary shift in the field of immunoprophylaxis. It critically examines the role of commensal microbes, microbial metabolites, and microbiota-derived materials as endogenous adjuvants, antigen carriers, or independent immunomodulators. The fundamental mechanisms explored include pattern recognition receptor activation, immune modulation by microbial metabolites, antigen presentation enhancement, and the generation of mucosal and systemic immune memory. This chapter also focuses on the importance of probiotics, prebiotics, postbiotics, genetically engineered microbial vectors, outer membrane vesicles, and fecal microbiota transfer in enhancing or replacing traditional vaccine approaches. The ethical, biosafety, and regulatory issues associated with live microbial therapy are also critically discussed, in addition to the issues of interindividual microbiome diversity and translational limitations. Finally, future directions are outlined, incorporating the concepts of synthetic biology, next-generation probiotics, and personalized microbiome engineering, thus positioning microbiota-based vaccine alternatives as a rapidly advancing area of research for the development of safer, more effective, and context-specific immunotherapeutic approaches.