I'm glad you gave me that link to the Drugs web site. I got confused along the line and thought they couldn't get their first vaccine until they were ten weeks. It's good to know they can get them at four weeks!
The vaccine comes in two bottles. One bottle has a little spongy thing in it that holds the inactive virus. The other bottle holds a blue activator. You have to use it within two hours of mixing it. For twenty-five chickens there's going to be a lot of waste. It says to burn the empty bottles, caps, and unused vaccine.
I'm not big on vaccines, so I'm holding off on giving any others. Honestly, since I only lost four out of fifty birds, I probably would not vaccinate at all if I hadn't seen what a HORRIBLE way it is to die. If I were a little more macho and could cull a sick bird, I might not be vaccinating them at all since the damage is already done and my flock is closed.
If my flock weren't already closed, I would vaccinate for anything that UTK told me was a problem around here AND that causes a carrier-for-life status. BYC has one of the best resources for different poultry diseases I've found:
https://www.backyardchickens.com/a/chicken-injuries-diseases-how-to-diagnose-treat-your-chickens It's in normal people language but has links to other reliable sources, like Merck's, so you can double check the info.
When I talked to the Pathologist (who was furious with me for calling so much) she told me that ILT was her "working diagnosis" as soon as she saw my hen. She told me the other thing she considered was cholera, so maybe that's common in our area, too?
Here's the really ridiculous thing. My hen was clean of the diseases they check for for NPIP. So, even though my Wyandottes have the potential to kill up to 70% of a flock they were introduced to (worst case scenario) I could still be NPIP.