The vaccine is labeled for chicks under 36 hours old. However, I have read studies where chicks have been vaccinated at 23 days and had better immunity than those vaccinated at 1 day. Another study vaccinated at 1 day and again at 3 weeks. The chicks had better immunity with the booster than if they had just had one vaccine.At what age can birds be vaccinated against Mareks? I read somewhere it had to be day old chicks. Is that true?
It takes at least 3 weeks for the chick's immune system to produce antibodies after the vaccine. They have to stay isolated and unexposed to Marek's birds or anything with the virus on it during this 3 week period. Some people think 6 weeks is safer to keep them isolated. You can vaccinate a bird at any age, but if it has already been exposed to the virus the vaccine will not do any good.