Improving the Quality of Lyophilized Animal Vaccines: A Review of Optimization Strategies for Freeze-Drying Processes

Vacuum freeze-drying, commonly referred to as lyophilization, is one of the primary processes in vaccine industrial manufacturing. It offers significant advantages, including a marked extension of the shelf-life of dried products, effective preservation of biological activity, and user convenience. However, in the production of animal freeze-dried vaccines, the diverse nature of antigens, the complexity of heat-stable protectant formulations, and variations in manufacturing equipment pose substantial challenges to process design for animal freeze-dried vaccines. Commercially available animal freeze-dried vaccines commonly suffer from antigen potency loss, insufficient product stability, low production efficiency and high manufacturing costs. Freeze-drying process optimization can markedly improve the quality of freeze-dried vaccines, with key evaluation indicators including vaccine stability, shelf-life, sample morphology, and residual moisture content. Focusing on multiple types of animal vaccines, this review summarizes research advances in improving the quality of animal freeze-dried vaccines from the perspectives of modifying material properties, enhancing freezing-stage regulation, increasing the specific surface area for drying, and optimizing heat conduction. Finally, future research strategies for animal freeze-dried vaccines are prospected. Although numerous approaches have been proposed to enhance the quality of animal freeze-dried vaccines, comprehensive considerations from multiple dimensions are still required to provide more holistic theoretical support for cost reduction and efficiency improvement in the production of animal freeze-dried vaccines.