CONCEPTUAL FRAMEWORK FOR A COST-BENEFIT ANALYSIS OF AVIAN
INFLUENZA VACCINATION IN SMALL SCALE PRODUCTION SYSTEMS:
THE CASE OF VIETNAM
M. PEYRE1, S. DESVAUX2, T. VU DINH3, T. PHAN DANG3, J.F. RENARD1, F. ROGER1
1.CIRAD,
Epidemiology Unit, France; 2.CIRAD, NIVR, Vietnam;
3.
Hanoi Agricultural University, Vietnam
INTRODUCTION
Biosecurity
level
Total poultry
production#
(%)
Poultry
producers#
(%)
Sector 1
Industrial integrated system with
birds/products marketed commercially
High
1-5
0.1
Sector 2
Commercial poultry production system
with birds/products marketed
commercially (no contact with other
poultry or wildlife)
Moderate to
High
10-15
0.5
Sector 3
Commercial/Semi-commercial system
with bird/products entering live bird
markets
Low to
minimal
20-25
5
Sector 4
Village or backyard production with
birds/products consumed locally
Duck pasture
minimal
65
>90
Definition
Highly Pathogenic Avian Influenza caused by H5N1 virus has become endemic in some developing countries and millions of birds have been
culled with large economical and sociological impacts. Since the end of the first vaccination campaign in Vietnam limited outbreaks in nonvaccinated domestic poultry have been reported. However, the virus is still circulating as confirmed by routine surveillance programs. Vaccination
is a useful tool to be used to control the disease, but the cost-benefit impact of different strategies needs first to be addressed at local level,
where implementation is decided. Cost and outcome of a vaccination campaign depend on the vaccination coverage rate, the size of the flock
and the risk faced. The choice of a vaccination strategy depends on the epidemiologic context and is function of the vaccine type (inactivated or
vectored), the targeted species (chicken, ducks, geese…) and the targeted poultry production types (breeders, layers, broilers). Here a
conceptual framework on the cost-benefit evaluation of various vaccination strategies is presented. Questionnaire based interviews will be used
to collect data at farm, district and provinces levels in order to parameter and validate this model. Using this model different vaccination strategies
could be evaluated and compared based on their cost-benefit at farm and provincial levels.
Fig 2. Provinces selection
Poultry density
Risk level
Vaccination efficacy**
STRATEGY
# National
Statistic Office, Vietnam
Table 1. Vietnam poultry production sectors*
RATIONALE
- Vaccination cost depends on the number of doses administered and the size of the flock.
- Vaccination benefit depends also on the number of doses administered (commercial benefit, « free »
protected flocks) and on the infection risk of the flock.
- Choice of vaccination strategy depends on the type of vaccine used (inactivated or vectored) and the
targeted species (chickens, ducks, geese etc…) and type of production (breeders, layers, day old
chicks, broilers)
The small scale production sectors (3 and 4) are at high risk for infection with minimal to low level of biosecurity
(Table 1) and where mass vaccination against HPAI is the most difficult to implement and to monitor.
The number of vaccine dose to be administered depends on the species and the breeding types (breeders,
layers, broilers). The risk of infection and the uncertainty of vaccine administration also depends on the
breeding systems: confined, enclosed with outdoor access, free-ranging, transhumant, mix population.
For our study, the small scale production sectors (3 and 4) were divided into 5 production categories (Figure 1)
according to the type of breeding and the confinement level.
4 provinces from the North and 6 from the South were pre-selected for the study according to the following selection criteria
(Figure 2): high poultry density, “at risk” level (19 “at risk” provinces identified from previous HPAI outbreaks**, virus circulation**
and recent outbreaks) , vaccination efficacy** (>50% sero-converted birds from post-surveillance sampling);
A 2nd selection will be performed based on the diversity of poultry production systems to be studied (by categories) within each
provinces and on the collaboration of the local authorities.
HAI DUONG
TAI BINH
The cost and benefit will be evaluated both at farm and provincial levels (or other appropriate administrative aggregation level).
There is a need to identify who is paying and who is gaining from each situation. Field surveys and analysis of national statistics
will be performed to evaluate:
NAM DINH
- Vaccination costs such as administration (vaccine price/dose,
equipment, staff…) training and post-vaccination surveillance.
VINH LONG
-Vaccination benefits by identifying the losses prevented
because of vaccination (bird value, sales keep up at local
markets…) and evaluating the cost of an outbreak in absence of
vaccination (market closure and quarantine for restricted area;
culling, disinfection and disposal of carcasses …)
CAN THO
BEN TRE
HAU GIANG
Fig 1. Categories for the study
(type and system of production)
TIEN GIANG
TAI BINH
MODEL DESIGN
Vaccination cost and benefit both depend on the number of vaccine dose administered. To study the cost-benefit impact of vaccination we have designed a
stochastic model based on different scenarios and outcome of vaccination (Table 2). The model is based on the calculation of a cumulative coverage
value, associated with the probability of administration of each vaccine dose. For example, for backyard poultry there is more or less chances of
administration of the 2nd dose depending on the distance from the farm to the collective vaccination centre or the farmer knowledge on vaccination
efficiency. Each dose could be linked to the previous one with a positive or a negative output: if there is an increased or a decreased probability for the
farmer to administer the 2nd dose when he has administered the 1st one, the doses are linked together; if the administration of the1st dose do not influence
the administration of the 2nd dose, the doses are independent. Different scenarios could then be anticipated, with different outcome of flock protection. The
scenarios could be run for each production category previously defined.
Model scenarios
Number of doses
Administration
Description
Scenario 1
2 primary
independent
2 doses, the probability of receiving the 2nd dose is
independent from the 1st one
1, 5
3 doses, the probabilities of receiving the 2nd or 3rd dose are
independent from the 1st or 2nd one
2 doses, the probability of receiving the 2nd dose is
increased with the 1st one
3 doses, the probability of receiving the 2nd or 3rd dose is
increased with the 1st or 2nd one
1, 5
Scenario 2
2 primary +
1 booster
independent
Scenario 3
2 primary
linked
Scenario 4
2 primary +
1 booster
linked
1
2
Sector 3, duck breeders
and layers outdoor
3
Sector 3, duck broilers
transhumant flocks
Categories
2, 3, 4
Sector 3, duck broilers
rice field feeding
4
Sector 4, mix of backyard
ducks and chickens
5
Main assumptions:
We will survey only known
vaccinated farms.
We assume the vaccination is well
performed and the vaccine used is
efficient.
Sector 3, chicken breeders
and layers outdoor
2, 3, 4
Table 2. Cost/benefit analysis model scenarios
2
OUTCOME & PERSPECTIVES
This preliminary stochastic model integrates all the variables linked to a vaccination campaign and is based on preliminary data obtained from international databases and field
missions carried out in Vietnam. Questionnaire based interviews will be used to collect data at farm and province levels in order to further parameter and validate this model. For the
selected production systems, the cost-benefit ratio of the vaccination will be evaluated within different control policies at the farm and at the provincial (and possibly national) levels.
Different control policies will be evaluated such as stamping out only the infected farm, stamping out all birds in a 3km buffer zone from the infected area. Different vaccination
strategies not yet in place in Vietnam will also be evaluated with a cost-benefit approach using this model: strategic vaccination of specific breeding type, specific breeding systems
or specific geographic zones.
An extrapolation of this model at a national level could be used by decision makers to evaluate and compare different vaccination strategies based on their cost-benefit ratio.
References:
*Guiding principles for HPAI surveillance and diagnostic networks in Asia, FAO expert meeting report, Bangkok, July 2004 (http://www.fao.org/docs/eims/upload//210749/Gui_principlesHPAI_july04_en.pdf)
Centre de coopération Internationale en Recherche Agronomique pour le Développement (CIRAD)
HA TAY
**Nick Taylor (FAO consultant), Do Huu Dung (MARD, Viet Nam). An analysis of data generated by post-vaccination sero-monitoring and surveillance activities, following HPAI vaccination in Viet Nam 92005-2006). Technical FAO and MARD report, January 2007.
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