One of the most important safety concerns with live PRRSV vaccines is the ability of the vaccinal virus to spread. The following laboratory and field trials were done to determine the ability of the Porcilis PRRS vaccinal virus to spread.
A critical parameter to determine spread is the reproduction ratio of a virus (Ro). Ro represents the number of animals that will be infected by one infected animal.
Method
Part 1
4 groups of 10 pigs each were used. In each group:
Part 2
Method as in Part 1. Vaccination with with live modified vaccine based on the American serotype.
Results
| Group | Seroconverted sentinels | Ro |
|---|---|---|
| A | 2 | 0.37 |
| B | 0 | 0 |
| C | 0 | 0 |
| D | 0 | 0 |
| Total | 0 | 0.11 |
| Group | Seroconverted sentinels | Ro |
|---|---|---|
| A | 3 | 0.53 |
| B | 3 | 0.53 |
| C | 1 | 0.2 |
| D | 1 | 0.2 |
| Total | 8 | 0.38 |
The R0 value observed in other trials with Porcilis PRRS has been below 0.1 (0.03-0.06)
In this field study, performed in a small PRRS virus negative herd in Denmark, the ability of Porcilis PRRS to spread from vaccinated to unvaccinated fully susceptible pigs and sows were assessed (Astrup, P. et al., 2002).
Method
Results
| Sample time | Vaccinated | Sentinel sows | Sentinel pigs |
|---|---|---|---|
| Start | 0 | 0 | 0 |
| Week 3 | 73 | 0 | 0 |
| Week 6 | 2 | 4 | 0 |
| Week 9 | 1 | 0 | 0 |
| Week 12 | 0 | 0 | 1 |
| Week 15 | - | - | 0 |
| Week 18 | - | - | 0 |
The study showed that spreading of Porcilis PRRS vaccine virus was very limited to only a few animals and ceased spontaneously.

Spreading of Porcilis PRRS vaccine virus was very limited to only a few animals and ceased spontaneously.