Vaccine development for porcine epidemic diarrhea virus and porcine Deltacoronavirus: Updated progress, challenges, and future perspectives.

Porcine Epidemic Diarrhea Virus (PEDV) and Porcine Deltacoronavirus (PDCoV) are considered the greatest threats to the world swine industry since they cause a very high morbidity rate in piglets. Although vaccines with various formulations have been tested and validated in different settings, they still cannot be considered to provide long-lasting, comprehensive protection against these pathogens under real-world conditions. This review provides a comprehensive and critical overview of parallel efforts to develop vaccines against PEDV and PDCoV, with particular emphasis on vaccine formulation strategies, virus strains used in challenge studies, and the geographical applicability of these vaccines. Recent advances in vaccine development are discussed, highlighting the use of newly developed adjuvants and advanced delivery systems to enhance vaccine efficacy, especially in terms of inducing mucosal immune responses. Rather than merely summarizing progress in vaccine development to date, this review presents challenges, including viral diversity, lack of cross-protection, and maternal antibody interference, which reduce vaccine efficacy. Additionally, we discuss novel directions for future research on broadly protective next-generation antigen-detection systems and integrated approaches targeting different porcine coronaviruses. Thus, this review offers an up-to-date, in-depth overview of the current state of PEDV and PDCoV vaccine research, while also outlining future perspectives to drive innovation toward practical and sustainable disease control.