Live vaccines contain naturally occurring mild pathotype or attenuated (weakened) viruses, bacteria or coccidia and are designed to elicit local and systemic immunity in birds. They are suitable for mass administration by water or spray.
Live vaccines in broiler breeders and table layers are most often used during rearing and multiple administrations are common.
Sometimes, live vaccines are used to boost immunity during the production period. This type of vaccine can cause a “vaccine reaction”, which is a mild form of the disease because of the replication of the microorganism in various tissues. Effects of these tissue reactions are the main concern in neighbouring barns when these live vaccines are given to pullets and birds in production.
A broiler breeder or a layer pullet flock will receive one or multiple applications of live bacterial, coccidia or viral vaccines. The spread of bacterial vaccines like E. coli or Salmonella is not a concern as most of the vaccine strains do not survive well in the environment and the tissue reaction is often quite mild. Regarding the coccidia vaccine, adult birds should have already had high exposure to various coccidia organisms in the environment and developed a strong immunity.
A typical vaccination program in Canada will include the following live viral vaccines: various strains of Newcastle Disease (NDV) and Infectious Bronchitis Virus (IBV) often given together; Infectious Bursal Disease (IBD); Avian Encephalomyelitis (AE); REO virus; Chicken Anemia Virus (CAV) (broiler and layer breeders); Fowl Pox (FP); and Infectious Laryngotracheitis (ILT). Not all these vaccines pose a risk if they are spread to birds in production. For example, adult birds have regressed bursas and the administration of an IBD vaccine to a younger flock doesn’t pose any risk to them.
Regarding CAV, AE and Pox, all flocks entering production must have strong immunity. If naïve birds in production get infected with an AE vaccine or a wild strain, a severe drop in egg production can be seen and the progeny (in case of breeders) will be affected.
With regards to CAV, only the progeny will be affected. The Pox vaccine causes a mild form of the disease and the virus can spread to other naïve birds. The main problems in the field for all three diseases occur when producers forget to vaccinate their flocks, vaccine is damaged, or the vaccine is administered improperly and flocks enter the production period with no protection. Regular serological (blood test) monitoring of flocks before the start of production for AE and CAV can prevent disasters during production. Similarly, all vaccinated flocks should be examined for takes to evaluate whether the Pox vaccine was given properly.
Infectious Laryngotracheitis virus causes lifelong infection in birds. There are three types of ILT vaccine: Tissue Culture Origin (TCO); Chicken Embryo Origin (CEO); and recombinant. Recombinant and TCO vaccines are safe and will not revert to pathogenicity, so they do not pose a risk to neighbouring flocks. However, CEO vaccine can cause diseases in other birds. For example, if we move CEO vaccinated birds into a barn with birds that are not vaccinated, an outbreak is imminent. This virus easily spreads by air so all susceptible birds in proximity will be affected, if not already protected.
Most commonly, problems with spreading a vaccine virus from pullets to birds in production occur with Newcastle and Infectious Bronchitis vaccines, especially more aggressive strains like La Sota. These vaccines will cause a mild and transient drop in egg production. They will also cause eggshell quality problems.
To prevent or minimize these incidents, farms should implement biosecurity measures. These measures should be especially practiced on the day of vaccination and for three to five days later. During that period, people handling the vaccine should never enter the production barns and no equipment should be shared between barns.
Outside of those days, the reality at many farms is that the same people take care of multiple barns. Washing hands and changing boots is best practice and will minimize the spread of many disease and vaccine viruses. Using different clothing between barns is an excellent but time-consuming practice.
However, even the best implementation of biosecurity can only be partially effective when dealing with airborne viruses. Having separate pullet and breeder/layer farms following “all-in, all-out” principles is the best option but can’t always be feasible for several reasons.
It is especially difficult to manage vaccine reactions when a live boost is needed in the face of an increased Infectious Bronchitis (and Newcastle) field challenge. In such situations, live vaccines are given every six-to-eight weeks to birds in production. The best advice for multiage farms is to co-ordinate vaccination between barns and to vaccinate on the same day.
In conclusion, producers should familiarize themselves with the risks that each of the live vaccines they use pose for the neighbouring flocks in production. If birds enter production with good protection and basic biosecurity measures are practiced, problems can be prevented.