### INTRODUCTION

### MATERIALS AND METHOD

### Research area and data

### Choice experiment

*i.e.*, the combination of ‘Non acceptance of vaccine administration with price of vaccine and compensation’). Respondents were then presented with the full set of 6 pair choices (totaling 12 individual profiles). Prior to answering the survey, respondents were provided an explanation of the hypotheses in the CE question (Table 2). 8)

*i*who chooses alternative

*j*in the alternative set

*C*

*can be written in the form:*

_{i}_{ij}is known for each individual

*i*and individual alternative

*j*. Without the covariates, with the exception of the error term ɛ

_{ij}, and without considering the individual attributes, the observable deterministic component of the indirect utility function V

_{ij}is:

*i*chooses alternative

*j*is the standard logit formula:

### Modified susceptible infected recovered model

Period of analysis is one year. Only one pig was infected at the beginning of the outbreak. The vaccination was administered immediately just after the first pig was infected.

The pig population mixes homogeneously in terms of piglets, grower pigs, boars and sows. 11)

All newly introduced (both newborn and from market) animals are susceptible.

All of the infected animals will be identified and culled, under the surveillance system.

The population size is constant as the recruitment rate is equal to the exit rate.

The pig population consists of those immune and those susceptible, but they are mixed homogenously and not distinguished in the market.

The infected animals will be identified and culled under the surveillance system (

*vI*(t)), or be sold to the market (*μI*(t)), or will recover and gain natural immunity (*λI*(t)).12)

_{0}” is defined as the average number of successful transmissions per infectious pig (equation 7). And the “Optimal vaccination proportion

*θ*” is defined as if the vaccination proportion exceeded the optimal vaccination proportion (equation 8), then incidence

*π*of an infection should decrease (Vynnycky and White, 2010). As the number of vaccinated pigs increases, the herd immunity proportion also increases. By decreasing the amount of susceptible people, the disease outbreak subsides.14)

*θ*) have to be vaccinated for administering the effective PRRS vaccination (equation 8, number of pigs that have to be vaccinated [equation 9] and number of pigs infected and culled in the situation with vaccination [equation 10]). Based on those results, we calculate the benefit of the PRRS vaccination.

### Costs-benefit analysis

*i.e.*private perspective and social perspective). In the social perspective, we consider the whole study area as one unit, therefore, we do not separate the farm’s expenditure and government’s expenditure for the PRRS vaccination.

### RESULTS AND DISCUSSION

### Choice experiment

### Modified susceptible infected recovered model

*R*

_{0}= 1.3, consequently, the optimal vaccination percentage is 26% (equation 8)16). However, the

*R*

_{0}in the study by Charpin et al. (2012) was 2.6, and accordingly the optimal vaccination percentage should be 68%. (The

*R*

_{0}value could vary due to different animal disease management circumstances in different study areas). For sensitivity analysis in the CBA model, we use those two optimal vaccination percentages to calculate the vaccination cost. According to Table 8, to increase the vaccination percentage above 26% or 68%, two ways can be considered. The first one is for government to provide a subsidy to reduce the vaccine price (reduce the price to 35,000 or 20,000 VND; Table 8, left part). The second way is for the government to provide compensation to cull infected pigs (provide compensation for 20% or 100% of market value; Table 8, right part). Based on the results of CE in Table 9, we set the value of the vaccination percentage ‘θ’, and ran the SIR model. 17) The total number of vaccinated pigs and infected pigs were estimated by equation 9 and equation 10. Therefore according to the results of the CE and SIR model, four available alternative vaccination programs were designed in two vaccination scenarios (Table 9).

### Costs-benefit analysis

*i.e.*the benefit is calculated by ‘loss from disease infection within SO’ minus ‘the loss from disease infection within SV’, because the comparison [control] value [loss from disease infection within SO] is relatively low, so the benefit from the farmers’ point of view is also relatively low). On the other hand, from the social perspective, we do not consider government compensation for the benefit calculation, the benefit of SV is much higher than the cost. It means when we consider both government and the pig farmers as a unit, SV has more economic benefit than SO.

### Conclusion remarks

*i.e*. Vaccination reduces infected and culled pig number, and then total pig production is increased).