Hathaway Hens - I ordered fowl pox vaccine to vaccinate mine - it takes a couple of days at most to arrive, but it takes a while for the disease to spread through the flock. When I had an outbreak about 2 years ago, I called Gary Butcher - the UF avian extension vet - and he recommended to vaccinate all that did not already have signs of disease to try to prevent illness in those, or minimize the severity. Most of mine had the dry form, but I had a few with the wet form, and sick enough to need to be brought inside and isolated from the rest of the flock (to give them a break, mostly, let them rest and recuperate without having to deal with the flock). I now vaccinate my new birds prophylactically. I don't like it when my birds get sick and it is a lot of work and worry to take care of them when the do! The ones that got the wet form survived - but I don't think at least one of them would have without my nursing care.
As far as lifelong immunity, I think in Florida the natural exposure is pretty common, and vaccinated birds will essentially get "boosters" naturally and keep the immunity without getting visibly sick. I don't know if that has been studied, but I think it is likely.