Yes, birds that are vaccinated for Marek's Diseaes can still get Marek's. The vaccine is effective 90-95% of the time, usually. It gives chickens time to build resistance to the disease, but due to things like secondary infections, weakened immune systems, or exposure to the disease before immunity can develop can all cause vaccinated birds to still get Marek's.
X2. One of the big things that makes the vaccine fail is early exposure after vaccine.let me explain.after the bird is vaccinated the bird must be kept from exposure (exposure meaning the outside and adult birds) for the very minimum of 14 days to allow the bird to build antibodies and immunity to the virus.if they are exposed before the antibodies had a chance to build resistance the bird will catch the virus before the antibodies form. Their are other reasons as well that vaccine fails like improper handling of the vaccine ect. Even in perfect conditions the vaccine is not 100% but for now that and breeding for resistance is our only defenses. In my opinion even though it's not 100% it is one of the most important things we can do for our birds. Mareks IS everywhere! ! So we should vaccinate and give immunity and antibodies time to build before exposure.
Yes. Chickens that were properly vaccinated with Marek's Vaccine, if exposed to the virus at ANY point in their lives, will contract the virus. Chickens that have built resistance (via the help of the Vaccine) will not show symptoms, but the virus will live in latency in their cells, and they have the potential to spread it. Chickens that have not built resistance (either because the virus challenged the immune system and won, or the vaccine was not given properly, or the chick was not given enough time to build resistance, etc), even with the vaccine, will become symptomatic and may die, or recover. It is hard to say. There are a lot of variables. If you want to do some more in-depth reading about the vaccine, you can go here:https://www.backyardchickens.com/a/the-great-big-giant-mareks-disease-faq In short: Yes, ANY chicken that is exposed to Marek's virus and inhales it will actually contract the disease, vaccinated or not. It's just that vaccinated birds have a higher chance (anywhere from 50% to 90% chance depending on the virus strain) to build up resistance and those that do never actually get "sick". The virus will still live in these birds, without harming them.
