Terrain theory, which was originally dismissed entirely when germ theory won, has been making a major comeback in the past decade or so under new names, such as

Terrain theory, which was originally dismissed entirely when germ theory won, has been making a major comeback in the past decade or so under new names, such as the "gut microbiome". Miasma theory as well, when it was originally proved wrong, has held back understanding of viral spread - experts stay away from aerosol spread and prefer droplet spread as much as possible because it's too similar to miasma.