Carl Creel was the only known Human who was able to survive to touching an Obelisk without needing an amputation. While he was briefly taken into S.H.I.E.L.D., Jemma Simmons and Leo Fitz took samples of his DNA, including blood. They noticed that whenever a sample of Creel's blood was added to Inhuman blood undergoing Terrigenesis, Creel's blood stopped and even reverted the process. As a result, Simmons, Fitz and Lincoln Campbell thought that Creel's blood could be the basis for a vaccine preventing further unwanted Terrigenesis. However, Daisy Johnson strongly opposed to the vaccine as she feared the governments would force Inhumans to use it should the vaccine fall in the hands of the authorities.
Despite Johnson's disapproval at the idea of the Terrigenesis Vaccine, Fitz and Simmons kept working on the project. Eventually, they were able to create a first version of the vaccine which could prevent Inhumans from undergoing Terrigenesis. Simmons suggested to try the vaccine on Andrew Garner before he completed his transition into Lash as his organism was still oscillating between the two forms, but Melinda May refused to do so.
However, Garner eventually surrendered to S.H.I.E.L.D. as he felt his full metamorphosis was close and he wanted to have a final moment with May. Garner was put in a Containment Chamber at the Playground and was injected with an IV of the vaccine. Despite that, Garner permanently transformed into Lash.
The Terrigenesis Vaccine is able to immunize Inhumans against Terrigenesis: therefore, Inhumans exposed to the Terrigen Mist would not create a Terrigenesis husk and remain powerless much like regular Humans. However, the vaccine cannot revert the effects of an already completed Terrigenesis, meaning that an Inhuman cannot become a Human again with the vaccine.