Notifiable Avian Influenza
Hazard Specific Plan

Appendix O: Notifiable Avian Influenza Vaccination Decision Tree

The objective of the decision tree for NAI vaccination is to demonstrate the various decision criteria that must be considered for controlling NAI. The decision tree in Figure O-1 shows the flow of decisions that must be taken; the descriptive text below proposes factors to consider when working from one decision box to the next.

The policy objective when dealing with NAI is stamping out. Traditionally this has been accomplished by depopulating infected premises and epidemiologically linked premises. In the 2004 HPAI outbreak in BC, pre-emptive destruction of premises within one kilometre was implemented and successfully controlled the spread of the virus.

More and more, pressure with regards to using other control options, such as vaccination, is being placed on regulatory authorities. These pressures follow a desire to prevent the killing of healthy, non-infected birds. In addition, preservation of genetics and of long lived uninfected birds is also desired. Therefore, vaccination must be considered as a potential control option.

Decision Box One

In decision box one, the decision maker must evaluate whether traditional stamping out of infected premises and of epidemiologically linked premises is sufficient to control the outbreak. Factors to be taken in consideration are described below.

1. Time to detection.
   
   Early in the outbreak, based on surveillance, tracing activities, and the discovery of newly infected premises, a determined action of whether important silent spread could have taken place must be made. This spread, prior to the first detected premises, will be important in determining the extent of the spread of the outbreak.
   
   When there is suspicion that a fair amount of silent spread could have taken place, movement to decision box two should be considered.
2. Extent of spread and methods of transmission.
   
   A single focus outbreak versus a multiple foci outbreak will have impacts on the physical resources to control them. Depending on how the virus is spreading, this could indicate that a wide geographical area could be affected.
3. Effectiveness of movement restrictions and biosecurity and biocontainment.
4. Density of commercial flocks in the area involved.
5. Species involved and involvement of non-commercial flocks.
6. The type of operation involved in the outbreak: commercial or non-commercial.
7. The type of production involved in the outbreak: production birds versus long-lived birds.
8. Physical and human resources required to deal with depopulation and detection activities.
9. Economical and trade impacts.

Decision Box Two

In decision box two, the decision maker must evaluate if additional culling strategies, such as pre-emptive destruction of birds on farms located within one kilometre of a known HPNAI-infected premises or the slaughter of birds located in the vicinity of an infected place in order to reduce the number of susceptible birds, would be sufficient to control the outbreak. Factors to be taken in consideration are listed below:

1. Legal authority for additional culling activities.
2. Resources available to accomplish this additional depopulation.
3. Social issues: public acceptance of depopulation of potentially healthy birds.
4. Economic and trade impacts.

Decision Box Three

In decision box three, the decision maker must evaluate if vaccination as a disease-control tool is possible. Factors to be taken in consideration are listed below:

1. Availability of an appropriate vaccine. The CFIA is working on getting a source of killed NAI vaccines.
2. Kind of vaccine to be used. At the present time, only killed NAI vaccines would be available.
3. Laboratory resources to deal with the surveillance of these vaccinated flocks. The vaccinated flocks would need to be tested on a regular basis in order to make sure that there is no silent infection. These active serology and virology surveillance activities would require a lot of laboratory resources.
4. Physical resources to vaccinate. Vaccination of poultry with a killed vaccine requires birds to be individually manipulated for the administration. If vaccination is possible, the vaccination policy objectives need to be defined. This would be done through decision boxes 4, 5, 6, and 7.

Decision Box Four

The objective of vaccination could be to protect rare birds, long-lived birds, or both. In that situation, the priority for vaccination could be as follows: rare captive birds (i.e., zoos), valuable genetic poultry stock, then long-lived poultry (i.e., multiplier breeder and egg layers).

Decision Box Five

The objective of vaccination could be to address the lack of resources for destruction. In that situation, a Vaccination Zone could be created where poultry would be vaccinated in order to reduce the number of susceptible animals in a certain infected region.

Decision Box Six

The objective of vaccination could be to prevent transmission to a non-infected area. In that situation, the vaccination could be applied as a firewall or protection band in order to protect poultry located in a non-infected region.

Decision Box Seven

The objective of vaccination could be to provide protection to poultry on a larger scale because of endemic status. In that situation, a blanket vaccination strategy would be developed.

Figure O-1: Decision Tree for NAI Vaccination

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Flowchart - Decision Tree for Notifiable Avian Influenza Vaccination

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