Astrocytes are fixed in brain tissue, so "single injection" means intracranial surgery.. the clinical bar for injecting anything into an Alzheimer's patient's brain is high enough that this is still a long way from a treatment.
2nd, the only injection is intravenous. It uses a kind of virus that has been specifically engineered to cross the blood-brain barrier. That virus has a payload which infects/alters astrocytes already inside the brain, and the astrocytes become aggressive at clearing amyloid plaques.
3rd, I agree that the road to a marketable therapeutic could be a long way off.