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I thought the vaccine doesn't work on older chickens. It is only for right after hatch. Am I remembering wrong? My vet told me that I think.
It's best to vaccinate as early as possible because you want to get them before they're exposed to the virus. They need 10 days for the full effects of the vaccine to kick in so you have to be careful to keep them isolated for at least that long. The older they are the greater the chance that they've been exposed. According to one veterinarian there are some studies that say it may be beneficial to vaccinate even when you know they've been exposed.
I thought the vaccine doesn't work on older chickens. It is only for right after hatch. Am I remembering wrong? My vet told me that I think.

It's best to vaccinate as early as possible because you want to get them before they're exposed to the virus. They need 10 days for the full effects of the vaccine to kick in so you have to be careful to keep them isolated for at least that long. The older they are the greater the chance that they've been exposed. According to one veterinarian there are some studies that say it may be beneficial to vaccinate even when you know they've been exposed.