In the human world there is a lot of controversy swirling about the efficacy and safety of vaccines. Which ones are necessary? Which ones are optional? What are the side effects?

There isn’t the same kind of polarization in the poultry community, but there does seem to be some confusion about vaccinations for chickens: What can we protect our birds from? Where do we get them? Do they really work?

I am by no means an anti-vaxxer, but I do think we all need to have some understanding about what any vaccine actually does; what are its limitations; and when to use, or not use, them.

When I started this piece I thought I’d be writing about a small handful of vaccines, but as it turns out there is a lot more to this topic than I expected. There are three types of vaccines, about a dozen different ways of administering them and twelve different illnesses that you can vaccinate for. As you can imagine if I write about each illness and detailed information about the appropriate vaccine it would be a really long read. Instead, I’ll offer an overview of some basics and write more in detail of separate posts about each pathogen.

How Vaccines Work

Vaccines help develop immunity by imitating an infection, without actually causing the illness, by triggering the body to produce T-lymphocytes and antibodies. Once the imitation infection goes away, the body is left with a supply of “memory” T and B-lymphocytes, that will remember how to fight that disease in the future. It typically takes a few weeks for the body to produce them so its possible that a chicken person infected with a disease just before or just after vaccination could develop symptoms and get a disease, because the vaccine has not had enough time to provide protection. Whenever you vaccinate birds they need to be kept away from unvaccinated birds for the period it takes for them to build immunity. They are not always 100% effective and can lose their efficacy (i.e. become weaker) over time.


Live vaccine: the active part of the vaccine is the live organism that causes the disease and can infect birds that haven’t had previous contact that pathogen. Vaccinated birds  are able to infect non-vaccinated birds if housed together (i.e. Marek’s Disease, Infectious Bronchitis, Infectious Laryngotracheitis).

Attenuated vaccine: the organism has been weakened so that it has lost its ability to cause the serious form of the disease. At worst, the birds may contract a very mild form of the disease, however, the vaccine still has the ability to trigger the immune system to produce antibodies.

Killed vaccine: the pathogen has been killed and is unable to cause the disease, but can trigger the immune system; immunity is weaker than that produced by live and attenuated vaccines.

Until I started doing research for this piece I thought that vaccinations were relatively simple – that the vaccine was administered by injection, orally or in their water. I knew that some, like Marek’s Disease were a bit more complicated in terms of storage and the amount of doses it is sold by. Little did I know that vaccines come in three forms (liquid, freeze dried and dust) and are given in a wide variety of ways:

Cloacal: uncommon; vaccine is introduced into to the mucus membranes of the cloaca with an abrasive applicator.

Drinking water

Water Vaccination

Feather follicle: feathers are removed and vaccine is brushed into the empty follicles.

In Ovo: applied via needle to five different areas of the egg: the air cell, the allantoic sac, the amniotic fluid, the body of embryo and the yolk sac. ( e.g. Marek’s Disease, Newcastle Disease, Infectious Laryngotracheitis (ILT) and Infectious Bursal Disease)

Intramuscular: needle into the muscle (usually the breast).

Nasal: dust or liquid drops in a bird’s nostrils.

Ocular: eye crops that make their way into the respiratory tract.

Oral: liquid drops that travel into the respiratory system or digestive tract before entering the body.

Spray: atomised spray that falls onto the chickens and is inhaled or enters the body as they pick at the droplets of vaccine.

Spray Vaccinations

Subcutaneous: injection under the skin.

Wing stab: needle is pushed into the skin of the wing.

Fowl Pox Vaccination

Some vaccines are given to day-old chicks, while others are administered right up to 16 weeks of age. All vaccinations should be given before a bird is potentially exposed to a pathogen.  If chicks are raised by a broody hen they can pick things up from their mother and once integrated into a flock, are vulnerable to a variety of illnesses carried in the soil, from contaminated feed or water containers, and by other birds. Their greatest threat is from older birds who are asymptomatic, but carriers for a whole host of pathogens.

Here is a list of the various pathogens that can be vaccinated for :

A Counterpoint To Vaccinations

This is a blog catering to small flock keepers, not large commercial operations where vaccinating on a large scale is economically more feasible and more necessary. An outbreak in a barn with 10,000 birds could spell disaster. Often vaccines require particular storage requirements, must be purchased in large quantities and used quickly.

Frankly, I don’t think it’s practical for someone with a handful of birds to routinely vaccinate. If you buy birds from a large hatchery you can often get them vaccinated for Marek’s and Coccidiosis. The former is a bit problematic in that it’s considered a ‘leaky’ vaccine – it will not stop your bird from becoming infected; the goal is to prevent serious illness. That bird, once infected, is a carrier of the virus for life and can infect any unvaccinated birds. If you do vaccinate it’s all or nothing – don’t mix birds that are protected with those that are vulnerable.

I’m more of a pragamatist.

I think that many of us imagine our bodies as pristine and only on occasion the subject of a bacterial or viral invasion. The fact is that there are many more trillions of bacteria in our bodies than there are human cells. Contrary to what advertising for anti-bacterial soaps would have you believe only 10% of bacteria are potentially harmful. The vast majority, the remaining 90%, are benign or actually helpful.

I would hazard a guess that the same is true for chickens. Their bodies are hosts to many varieties of ubiquitous bacteria, viruses and parasites that under normal circumstances live in balance. It’s often when birds are stressed or immuno-compromised that the balance shifts and those pathogens and parasites are allowed to reproduce in large numbers, causing illness.

The best strategy for keeping our birds healthy is to ensure they are healthy to begin with. That sounds like common sense, but a sick bird is more likely to become symptomatic with a secondary infection than a healthy bird to become sick at all.

  • We can do that by making sure we start out with healthy stock – robust chicks that are the offspring of two disease-free parents.
  • Young birds (less than six months old) are vulnerable due to their lack of exposure and resistance to pathogens.
  • Feed your birds the appropriate food for their stage in life. Young birds fed layer pellets, with calcium levels in excess to their requirements, can suffer life-long or life-threatening kidney damage, like gout.
  • Make sure your birds don’t get dehydrated and always have access to fresh, clean water.
  • Provide nipple-style waterers that are less likely to harbour pathogens due to fecal contamination.
  • Routinely clean your coop and remove poop that might carry diseases.
  • Practice biosecurity between pens and between farms.
  • Quarantine new birds.
  • Stress is a huge factor in allowing pathogens to become unbalanced. Monitor their pecking order, new additions, predator attacks or any events that might be construed as stressful.
  • Remove sick birds from your flock and treat or euthanize.
  • Understand that birds who have recovered from an illness may be life-long carriers. They may appear healthy, but are potential incubators for that pathogen.
  • No flock is without parasites and pathogens – that’s a given for birds who are pecking in the soil and are exposed to feces from rodents and wild birds. Our job is to manage the balance of those bacteria so there is no heavy load.

Whether you vaccinate or not, understand how your birds are protected and any limitations of those vaccines. Remember if you vaccinate some birds you need to vaccinate them all or you’ll be leaving those birds vulnerable to viruses carried by asymptomatic carriers.

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