What are the risks of Avian Influenza vaccination?

Even when an efficacious vaccine is used, the risks identified with AIAvian Influenza vaccination are the same as those identified for other vaccinations

Even when an efficacious vaccine is used, the risks identified with Avian Influenza vaccination are the same as those identified for other vaccinations, against the Newcastle disease, Infectious bronchitis, Marek’s disease or any other diseases.

Over-confidence in vaccination

Vaccination is a powerful tool in the control of infectious diseases, but can never be a stand-alone solution. Most of the time vaccines protect against the disease, i.e. the consequences of infection, and not against the infection itself, so that the field virus can still infect, replicate and be shed. There are only very few veterinary vaccines that have the capacity to totally block the pathogenic agent, which is scientifically called “sterile immunity”. Even if limited, or reduced, the shedding of the challenging infectious agent is always possible. Thanks to vaccination, the risk is lower, but not totally eliminated. Biosecurity programs always need to be present and strong, having in mind that the best protection against any kind of challenge is simply to avoid the challenge.

Poor vaccine application

In every flock, there will be some birds missed during the vaccination process. It is generally acceptable for an epizootic disease like Avian Influenza (or Newcastle Disease) if the percentage of missed birds remains low (less than 3-4%) and if the challenge pressure is not constantly applied to every chicken (as it is for the Infectious Bursal Disease of Marek’s disease).

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Vaccination at the hatchery is much easier to control and consequently, far more reliable than any other type of vaccination, in particular compared to vaccination on the farm, and this is why hatchery vaccination is preferable ( #18 ). This does not mean that big mistakes cannot be made. There are flocks where as many as 50% of chickens are improperly vaccinated, so monitoring and assessment of vaccination are necessary.

When it comes to using a vaccine like the vector rHVT H5, Vectormune AIAvian Influenza, it is important to keep in mind that this vaccine does not spread, so that if not vaccinated, the chicken will never be protected by the vaccine received by its hatch-mates. For this reason, all the critical steps of the vaccination process including storage, distribution, reconstitution, injection need to be regularly monitored.

Another important advantage of vaccination in the hatchery is the elimination of the well identified risk of transmission of Avian Influenza viruses by the vaccination crews going from farm to farm.

Factors of a good immune response

Vaccination stimulates the immune system to produce an immune (protective) response. If the immune system is compromised, at the time of vaccination or later, then protection is also compromised. This is why vaccination works so well on some farms and less well on others. Quality of day-old chickens or day-old poults, housing, feed, environment, farming, ventilation, as well as control of concurrent infections are also critical factors in the success of vaccination


The fact that Avian Influenza is still endemic in countries where vaccination has been applied is often presented as an argument against vaccination. In fact, this situation is a consequence of many factors including the following, which have been already detailed above:

  • In all countries, the AI vaccines used were mostly, if not exclusively, of the classical inactivated type and for this reason, were unable to:
  • The vector Fowl Pox ( rFP-HAHemagglutinin) vaccine was tried in Vietnam, as well as the vector Newcastle Disease (rNDV-HA) in China, but they were soon found to be inefficacious when administered to chickens carrying MDA against AIVAvian Influenza Virus or NDVNewcastle Disease Virus.
  • Vaccination was implemented more or less as a stand-alone solution, without comprehensive monitoring plan of the infection.
  • Dedicated technical and financial means were generally poor so there was no coordinated action plan and no compensation system for farmers affected by the disease. This latter point led to farmers trying to save surviving birds, taking them to the market and doing so, helping the disease to spread.

The vector rHVT-HA5 vaccine, Vectormune AI, has been introduced recently in Mexico, Egypt and Bangladesh but, as of today, only on a limited scale so that the benefits cannot yet be clearly evaluated. However, a survey conducted in Egypt under the supervision of FAO and CIRAD (a French NGO) has shown that vaccination at the hatchery with this vaccine was clearly beneficial       ( #18 ).

Find out more about this new vaccine.