Marek’s Vaccine For Older Chickens

Marek’s Disease is as confusing as it is frightening and devastating. Because it manifests a variety of different symptoms and many of those same symptoms occur in other diseases, many flock keepers aren’t aware that Marek’s is lurking in their flock.  And many flock keepers don’t realize that no matter how stringent they are in their husbandry practices and no matter how meticulously clean their coop, their flock still has a high potential for Marek’s.  If you’re concerned about the potential for Marek’s in your coop, I suggest you take this easy two-step Marek’s detection test right now.  1—Go to your coop.  2—Open the door and look.  Do you see chickens?  Then your potential for Marek’s is high.  This, of course, is an exaggeration to make a point, but only a slight exaggeration. 


Marek’s Disease is by far one of the most common illnesses in small flocks and not treatable once the clinical signs have begun. Yet, it is one of the most preventable illnesses out there. There has been much discussion and misinformation about Marek’s Disease. So here are some clarifications concerning this disease.

Marek’s Disease affects chickens and is caused by a chicken herpes virus. It will not make people sick. Like many herpes viruses, once an animal becomes infected, it will be infected for life. Not all infected birds, however, will get sick. The percentage of clinically sick birds in a flock depends on the strain of virus (some virus strains are more virulent than others) and the breed of bird. Leghorns and light egg-type breeds tend to be more vulnerable to disease than meat type breeds. Silkies in particular, are highly susceptible to Marek’s Disease. The percentage of illness and death in a flock can be anywhere from 1% to up to 50%. The clinical disease is typically seen between 6 weeks to 30 weeks of age. But Marek’s Disease can develop in older birds as well.

Features of Marek’s Vaccine For Older Chickens

You may be a little discouraged after having read what I had to say about genetics and biosecurity and perhaps you’re holding great hope for what I have to say about vaccination.  Well, here’s the good news:  Vaccine manufacturers and hatcheries will tell you that vaccines have an effectiveness of greater than 90%.  While that statistic is undoubtedly true since it’s based on hard evidence, you need to bear in mind that for the vaccine to work, it has to be administered correctly and at the right time.  Also, since the virus is capable of mutating to more resistant forms, the current vaccines will without a doubt become less effective as time goes on.  There are currently three different varieties or “serotypes” of vaccine—each is made from a different strain of the virus:

Serotype 3 vaccine is made from a strain of Marek’s virus that occurs in turkeys that does not cause disease in chickens.  It’s also referred to as Herpes Virus turkey (HVT).  It was developed in the 1970’s in Michigan and is the oldest of the vaccines, thus it’s the least effective serotype due to mutated resistance. 

Serotype 2 vaccine is made from a strain of virus that naturally occurs in chickens but doesn’t cause tumor formation or disease. 

Serotype 1 vaccines (there are several of them) are made from the disease-causing virus.  These vaccines are “attenuated”—they’ve been manipulated in a laboratory to weaken their ability to cause disease but they still cause immunity in the chicken that receives the vaccine. 

Bivalent and Trivalent Vaccines:  Serotype 1 vaccine is not very effective, but when given in a “bivalent” vaccine combined with Serotype 3 vaccine, the vaccine is more effective than either serotypes 1 or 3 given separately.  Most hatcheries, as standard practice, give the bivalent vaccine or a trivalent vaccine that contains all three serotypes. 


  1. Mix turkeys and chicks together to prevent Marek’s Disease so the chickens will be exposed naturally to turkey herpes virus. This is not correct! Not only will the chickens not get Marek’s Disease protection, but turkeys might be exposed to other common chicken diseases such as Mycoplasma and Blackhead.
  2. Don’t vaccinate birds so that the survivors will become resistant. Genetic disease resistance takes decades to develop and so far, has not been successful with Marek’s Disease. If it were successful, one would think the commercial chicken genetic companies would have developed resistant chickens by now.
  3. Only vaccinate a few birds and the vaccine will leak and protect the other chickens. This is incorrect. Every bird needs to get a full dose of vaccine before they become exposed to the actual disease-causing virus. This is the only way to achieve protection.
  4. Don’t vaccinate birds because this vaccine is dangerous and might make the chickens ill. If careful mixing of the vaccine in a sanitary manner is not followed, the birds may get a bacterial infection. Wash hands, use a sterile needle, and avoid touching the needle with hands or any soiled object. Use only commercial vaccines. The companies making these vaccines are testing for potency and making sure the vaccine does not become contaminated with other diseases.

Prices of Marek’s Vaccine For Older Chickens

 $25.00-$50.00 / Piece

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