I wish there was more information. Can't tell if this just happened once or if this repeats.
If you mean this paralysis came on suddenly, like over night and continues, I would guess some disease or possibly something toxic in their feed or environment.
Are there any other symptoms, like runny eyes, bubbles in the eyes or congestion? Are they still alive?
Without more information, there's not much more to say. I would need to know things like: how old they are, did you add any new chickens or poultry recently, how long have you had them, as well as if this has happened more than once, what are you feeding, are there any toxins they might have gotten into, has this affected each member of the flock at the same time?