To Vaccinate or Not? A Family Guide
Marek’s Disease and Your Flock:
Marek’s disease is a viral infection in chickens that causes tumors, paralysis, and sometimes death. For families raising poultry, deciding whether to vaccinate can feel complicated. This guide breaks down the decision process based on flock goals, explains what early symptoms to look for, and helps distinguish Marek’s from other conditions.
Should You Vaccinate? Pros and Cons
Pros of Vaccinating
Protects birds from paralysis and death: Vaccinated chickens rarely die from Marek’s disease.
Reduces visible outbreaks: Improved chance of your flock appearing healthier.
Peace of mind: Especially valuable for families raising chickens as pets and prioritize survival over eradication of the disease.
Cons of Vaccinating
Vaccine is “leaky”: Birds can still carry and shed Marek’s virus, potentially infecting unvaccinated chickens and unknowingly end up with a disease in your flock.
Does not improve the breed through natural selection: Vaccination can mask weaker genetics, so natural resistance isn’t tested in the flock. Unvaccinated birds that survive have a natural resistance and carry lifelong immunity once recovered.
Dependency on vaccine: New chicks will need vaccination if introduced into the flock later, or they will remain vulnerable.
Flock Goals as Decision Makers
Vaccination is a very personal choice. We find that families are 50/50 split on their decision to vaccinate even when we offer vaccination for free.
Your flock’s purpose may influence your vaccination decision:
Pet / backyard hobby: Families prioritize the bird’s health over genetics; early loss is emotionally painful. Typically Choose to Vaccinate.
Egg production for home use: When the number of eggs your hens produce matters, the risk of losing layers to Mareks could be seen a reason to vaccinate. Knowing that Mareks is hard to detect in vaccinated hens and that it can result in the hens laying less eggs, it could be seen as a reason to maintain an unvaccinated flock. Flexible / case-by-case personal decisions.
Self-sufficiency / breeding resilient stock: Want birds that survive without human intervention; build natural resistance. Typically prefer unvaccinated flock members.
Breeding for Breed Improvement & True Health: Want to ensure that there are no hidden diseases or illnesses that are covered up by vaccinations. Typically prefer unvaccinated flock members.
Breeding for Profit: Want to ensure all hatched birds can sell regardless of hidden illnesses as long as the birds can thrive with the assistance of a vaccination. Typically choose to vaccinate.
Show / exhibition birds: Maintaining appearance and consistent health is key; Marek’s can ruin show birds. Typically Choose to Vaccinate.
Mixed approach / small hobby flock: Some breeders vaccinate only new chicks or maintain separate vaccinated/unvaccinated lines. Flexible / case-by-case personal decisions.
Early Signs of Marek’s Disease
Marek’s disease can be subtle at first. Watch for:
Slower growth than flock mates
Reduced activity or reluctance to move
Ruffled feathers and poor grooming
Loss of appetite or weight loss
Pale comb and wattles
Crop not emptying fully
Intermittent or mild lameness
Isolation from the flock
Paralysis (leg or wing drooping) and “gray eye”
Catching it early is tricky but possible by observing behavior and condition regularly.
More Common Treatable Conditions That Mimic Marek’s
How to Tell Them Apart
Vitamin B2 deficiency (“curled-toe paralysis”): Toes curl, chicks <8 weeks, sometimes tremors: Affects very young chicks, responds quickly to supplements: Correct diet / supplement B2 and confirm crop is not blocked
Vitamin E / Selenium deficiency: Incoordination, tremors, “crazy chick disease”: Sudden onset, not progressive wasting: Correct feed / supplements and confirm crop is not blocked
Coccidiosis: Depression, ruffled feathers, bloody/watery droppings: Acute, flock-wide, no paralysis: Anticoccidial treatment, sanitation
Botulism: Flaccid paralysis, neck droops, rapid onset: Sudden, affects multiple birds exposed to toxin, no wasting phase: Remove contaminated feed/water, supportive care
Injury / trauma: Limping, wing droop, one bird: No progressive wasting, no other birds affected: Isolation, supportive care
Tip: Multiple birds showing gradual paralysis and weight loss is the hallmark of Marek’s. If there is just one bird having difficulty or is a sudden onset, it is likely something else.
Managing Your Flock
Vaccinated flocks:
The Marek’s vaccine is given at day old for optimal protection. You may vaccinate later, however, it needs to be given at least 7 days prior to being exposed to be effective.
Important: Birds are not immediately immune. It generally takes about 7 days after vaccination for the vaccine to provide significant protection. During this window, chicks are still vulnerable to infection if exposed to the virus. You should not mix birds from different sources whenever possible during this vulnerable timeframe.
Monitor for early signs, but expect very low mortality once immunity develops.
Unvaccinated flocks:
· Be vigilant, as outbreaks can be severe. Observe all birds daily for early symptoms.
· Isolate affected birds and practice good sanitation to reduce virus load in dust, litter, and housing.
· Unvaccinated birds that survive have a natural resistance and carry lifelong immunity once recovered. This becomes a desired trait to breed for.
Mixed flocks (vaccinated + unvaccinated):
· If your flock is never exposed to Marek’s you will not notice a difference between vaccinated and unvaccinated birds.
· Adding unvaccinated chickens to a vaccinated flock that was previously exposed can result in high mortality for the newcomers, because the virus is already circulating silently within your flock.
· Consider keeping unvaccinated birds separated at least 50’ from vaccinated flocks if you are unsure if the vaccinated flock has been exposed.
· If you have an existing flock of unvaccinated chickens and add vaccinated chickens that were never exposed to Mareks, you will not notice any differences unless your flock is later exposed to Mareks.
When in doubt:
· When in doubt, Isolate out! Isolate and sanitize all equipment and things that come in contact with the flock. Rule out treatable conditions like coccidiosis or vitamin deficiencies. Unfortunately, Marek’s is not treatable, so the best you can do is provide nutritional treatment and see if recovery is possible.
Nutrition & stress management:
Strong nutrition and minimizing stress help all birds resist disease complications, regardless of vaccination status. Reducing stress in a poultry flock is essential for their health, growth, egg production, and overall welfare. Providing adequate space solves most flock concerns such as pecking, low egg production due to stress, and illness prevention.
Summary
Choosing whether to vaccinate for Marek’s disease depends largely on your flock’s goals and tolerance for risk:
Pet / egg flocks → Vaccinate to protect birds and reduce stress.
Breeding / self-sufficiency flocks → May choose not to vaccinate to build natural resistance and accept potential loss to ensure a known disease-free flock. Regular observation, early detection, and understanding what else could mimic Marek’s are essential for all flocks.