preserve (someone or something) against (something)
To keep someone or something safe or protected from something. Many of these chemicals used to preserve our foods against decay have deleterious effects on our health. Parents are all so preoccupied with preserving their children against danger that they end up sheltering them from many of the things that make childhoods memorable.
preserve someone or something against something
to guard or protect someone or something against something. (Stilted or old-fashioned in reference to people.) I hope that the vaccine will preserve us against influenza. There is nothing in the jam to preserve it against spoilage.