By saying to weeks I suppose you are referring to one week old. Now fowl pox can affect birds of all ages however the prevalence will depend on the management level with mixed ages birds more prevalent to early infection than all in all out. For short term protection, attenuated tissue culture origin (TCO) pox vaccine in combinations with mareks at day old depending on the vaccine availability otherwise for long term protection chick embryo origin type of fowl pox vaccines is preferred at between 3-6 weeks of age via wing web stub.