There is a fowl pox vaccine available at several online stores. It has to be given correctly and take a few weeks to create immunity. It won't work if the chickens have already been exposed to the pox virus.
Separation of affected birds can help to contain it, since pecking of scabs or shed scabs can help to spread the virus. Permethrin is a safe insecticide for chickens' housing. I have even heard of friends in Florida using hanging strands of screen over doorways to keep them out of the coop. Keeping puddles of water cleaned up, and changing drinking water daily can keep mosquito larvae from collecting and hatching.