Q: I got the Marek's vaccination for my chickens, but one chicken seems sick! Is the vaccination not working?
A: If your chicken received the Marek's vaccination, she will most likely be protected from the symptoms of Marek's disease, but a small percentage of birds will still get sick with Marek’s, even when vaccinated. Also, there are many other illnesses chickens can get. For instance, if you got a whooping cough vaccination as a kid, you can still get the flu, or liver disease, or bronchitis, or an ear infection, or lyme disease and so on. The same goes for your chicken. Vaccinating for Marek’s disease will not protect your chicken from all sicknesses, only Marek's.
As always, if you think your chicken is sick, you will want to contact a veterinarian to get a firm diagnosis and treatment options.