Current knowledge on PRRS virus immunology is still limited but it seems clear that modified live PRRS vaccines (MLV) are a reasonable choice for the immunization of pigs. Recently, interest in intradermal vaccination in swine has increased due to research into skin and subcutaneous tissue immunology and the possibility of using needle-free injection devices (NFIDs). The use of NFIDs in the swine industry offers some advantages over conventional needle-and-syringe methods, especially due to the reduced pain and stress to pigs and the increase in the uniformity of the dosage administered to the herd.
The MLV vaccine UNISTRAIN® PRRS has recently obtained the indication for intradermal administration with Hipradermic®, a needle-free injector with connectivity developed by HIPRA for the intradermal vaccination of pigs. A multicentre field trial was conducted under field conditions in order to demonstrate the clinical protection provided by the intradermal administration of UNISTRAIN® PRRS in swine with Hipradermic®.
A multicentre, randomized, double-blind trial was carried out in 1532 pigs distributed between 3 commercial farms (farm Nos. 1, 2 and 3) with a previous history of outbreaks of PRRS. The animals on each farm were randomly divided into two treatment groups. Group A (n=693) was vaccinated once at 3-4 weeks of age (day 0; d0) with 0.2 ml of UNISTRAIN® PRRS vaccine (103.5 CCID50/animal) administered intradermally with Hipradermic®. Group B (n=839) was injected with 0.2 ml PBS (phosphate buffered saline) also intradermally with the same device. All animals included in the trial were individually identified. An outbreak was considered to have occurred when at least 10% of the pigs showed respiratory symptoms and it was confirmed by PCR and serology. The parameters used to assess the efficacy of the vaccine against a PRRS virus outbreak were: viraemia, lesion in PRRS virus positive lungs, clinical respiratory signs, mortality, average daily weight gain (ADWG) and individual number of antibiotics administered throughout the study. Virus detection was carried out by real time RT-qPCR.
A clinical PRRS outbreak was confirmed on two farms (Farm 1: outbreak beginning at day 76 with a PRRSV 95% ORF5 homology; Farm 3: outbreak beginning at day 148 with a PRRSV 88% ORF5 homology) and thus only the results of these two swine farms are shown.
Statistical differences were observed on both farms between the vaccinated and the control group in the reduction in viraemia around and during the outbreak (farm 1: d45 and d90; farm 3: d90, d120 and d150). A statistically better mean clinical index assessment was also observed during the outbreak and specifically on days 76, 78 and 82 (farm 1) and on day 152 on farm 3. Mortality in the fattening period was also statistically reduced.
Percentage of mortality at the fattening unit during the trial:
The percentage of lung lesions among PRRSV positive animals (farm 1: 63.9% control vs 33.3% vaccinated; farm 3: 90.0% control vs 33.3% vaccinated) and ADWG from weaning to slaughter were also statistically better in the vaccinated group than in the control group.
ADWG (kg) from weaning to slaughter:
On farm 3, a statistical decrease in the percentage of animals treated with antibiotics during the fattening period was also observed.
Percentage of treated animals at fattening unit per farm:
The results obtained allow us to conclude that UNISTRAIN® PRRS administered in piglets by the intradermal route through Hipradermic® is effective when administered according to the recommended vaccination program and is a useful tool for the reduction of viraemia and the negative clinical and productive consequences of PRRS virus infection in swine in the field.