Here are some FAQs about the vaccine:
VACCINATIONS
How does the vaccine work?
The most important thing to know about chicken Marek's vaccines is that they are not a cure, they are not an immunity, and they are non-sterilizing. In short, this means that giving a chicken a vaccination gives the chicken's immune system exposure to a related virus (usually HVT MDV-3, HVT stands for HerpesVirus of Turkeys). This related virus cannot cause symptoms in a chicken, but gives the immune system something to target and build a resistance. The hope here is that if the chicken is ever exposed to Marek's virus later in life, that the immune system will react appropriately to fight off progression of the virus into lymphomas, and the chicken will not develop the symptoms.
Effective vaccination in chickens will not ever prevent the chicken from becoming infected with Marek's virus. In fact, it can be assumed that any chicken exposed to the virus will become infected. Instead of preventing infection, the vaccine builds resistance within the immune system which in turn will prevent lymphoid tumors from forming. As these tumors (neoplasms) are the most fatal part of the disease, effective vaccination can save the chicken's life.
Should I vaccinate for Marek's?
This is a personal choice. The best way to make this choice is to determine the risks for exposure to Marek's, evaluate your goals with your poultry, and understand the disease. If you are not sure if you want to vaccinate at all, you are in the right place. Keep reading and make the best informed decision that you can!
How effective is the Vaccine?
This is a very complicated question with a complicated answer. There are many variables at play, including: Which vaccine(s) were administered, if they were administered correctly, the breed of the chicken, the genetics of the chicken, the natural resistance vs. vaccinated resistance in the chicken, how the chickens are kept, overall health, what "strain" of Marek's the chickens are exposed to, etc.
All things being equal, you will see many hatcheries and vaccination manufacturers claim 90% or better effectiveness. This has been true in years past. Today we are seeing mutated strains of Marek's that are challenging the older vaccines. The most commonly used vaccine (derived from MDV-3, which is Turkey Herpesvirus/ HTV) is also unfortunately the 'oldest' and has been used so widely on so many chickens (mostly commercial chicken keeping) that mutated strains can now challenge it and overcome. Some research suggests that the virus is mutating faster than previously thought, to remain virulent in spite of vaccinations. It is also remember that the 90% figure comes from proper vaccinations of chickens kept in commercial farms, most of which in the USA employ long indoor housing, with chickens in great densities, that often practice "all in - all out" keeping, and can properly deep clean all indoor surfaces. Our backyard chicken keeping methods are quite a bit different. We have much less control over environmental factors, and often (and to the woe of some) we swap chickens at meets, sales, state fairs, retired battery hens, craigslist, etc etc.
These conditions and the existence of new strains (for more details, read Disease Details below) are causing the common vaccine to be 'challenged'. So, in any given flock, more than 10% of vaccinated birds that are exposed to a more virulent strain might succumb to Marek's. It's not necessarily common that this happens, but it has to be mentioned because it's a lot more than the 10% of yesteryear. Some flock keepers have experienced more than 50% loss to vvMDV-1 (very virulent Marek's).
When should I vaccinate?
Marek's vaccinations should be administered to chicks that are less than 36 hours out of the egg. Within 24 hours is recommended. This is to give the undeveloped immune system the proper amount of time to build resistance to the harmless MDV-3.
Most hatcheries will vaccinate day-old chicks for you. The cost of vaccination is typically less than $0.30 at the time of writing. It is even less at some hatcheries.
You can vaccinate your hatched chicks at home within this 36-hour period, but all proper vaccination procedures must be followed in order to guarantee an effective vaccination. Always follow all pharmaceutical guidelines offered by the manufacturer of the vaccine.
Chickens that were not vaccinated by 36-hours-old should never be considered “properly vaccinated” and should not be sold or traded under the pretenses that they were vaccinated for Marek's.
There is also some research that suggests that a follow-up vaccination at the age of two-three weeks old may increase the chances of immunity. Find out more: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2643530/
How long does it take for the vaccine to work?
After vaccination at hatch (before 36 hours of age!), it is important to isolate (quarantine) chicks from exposure to Marek's disease for a minimum of 3 weeks, for the maximum benefit and best chance for the vaccine to develop resistance within the immune system. Some chicken keepers prefer to go longer periods of time, while others do not. Exposure to other chickens (or their dander, which is easily carried on your clothes and hair) before the 3 weeks is over is not recommended. Exposure before 3 weeks should be avoided at all costs if you suspect or know your flock already has Marek's disease and are carriers. Exposing vaccinated chicks before three weeks may compromise the effectiveness of the vaccine.
My chicks were not vaccinated. Can I vaccinate after the 36 hour period?
Here is where we enter into some theory, and you must not take any of this is rock solid fact. It's hardly close, and based only on the speculations of chicken owners and their real life experiences with this disease.
Vaccinating chickens that have not been previously (properly) vaccinated cannot hurt healthy birds.
It may or may not increase their chances of building resistance if they are later exposed to MDV.
If you vaccinate chickens older than 36 hours, you should not consider them properly vaccinated, but at the same time it may give them a better chance than no vaccine at all. The younger the better, of course.
If you have chickens that have already been exposed to Marek's virus, there is little chance and no findings to suggest that vaccination will help them at this point. It will not cause a healthy bird any harm but it is probably a waste of time. If it makes you feel better, you can try, but do not expect much from it.
More info here for further reading: https://www.backyardchickens.com/a/the-great-big-giant-mareks-disease-faq
