What does it mean to lyophilize a vaccine?

Lyophilizing a vaccine refers to the process of freeze-drying it. This technique involves first freezing the vaccine and then reducing the surrounding pressure to allow the frozen water in the vaccine to sublimate directly from a solid to a gas phase. The purpose of lyophilization is to remove moisture from the vaccine while preserving its biological activity, stability, and shelf-life. This process is crucial because it allows for the long-term storage of vaccines without the need for refrigeration, making them more accessible especially in areas where cold chain logistics can be challenging. The end result is a dry powder that can be reconstituted with a liquid, typically a diluent, before administration.