Google it. There's all you need to know on there, plus a lot you don't. Basically, if they have the skin type it will slowly get better but run through the flock, if it's the one on the internal membranes you're going to lose a lot. Someplace suggested vaccinating the rest of the flock because the virus spreads so slowly that it should have time to get working before they've all gone down with it. I don't see that it would harm the ones which are incubating the Pox.
Apparently Fowl Pox is found all over the world - I've never come across it.....