It turns out the hens I got are vaccinated.
I guess I should've done more research before diving in! What are some of the cons of vaccinating chickens, other than it weakening their immune system? I found some unvaccinated chickens, is it a terrible idea to bring them into the flock, even if I keep them separated for a while to build up their gut flora to my backyard environment? Do the vaccinated chickens have any impact on the eggs they lay? Basically, is there going to be any crud in the eggs we eat from the vaccination? Similar to antibiotics I guess...?