Furthermore, the study demonstrates that vaccination does not produce potentially harmful inflammatory reactions in the young pigs, confirming the vaccine’s safety profile.

The study, which was conducted by Zoetis and published in Porcine Health Management, looked at immune responses to PRRSV following vaccination of day-old pigs with a modified-live vaccine based on PRRSV-1, a European strain of the virus.¹

“PRRSV is known to interact with the host’s immune system. Some strains can induce a slow and weak innate immune response and a delayed adaptive immune response,” explained Monica Balasch, PhD, director of research and development at Zoetis and one of the study’s authors.

“Moreover, the immune system of the neonatal pig is not fully developed. This has created concerns about using live vaccines in young pigs, so we did this study to confirm whether pigs could safely and effectively mount an adequate immune response to PRRSV when vaccinated at 1 day of age.

“Our results confirm that pigs can be vaccinated on day 1 without impeding innate or adaptive immune development. This helps ensure the young pigs are protected from PRRSV early, before they enter a period of high risk.”

Study design

The study was conducted in 25 pigs born to PRRSV-seronegative sows. The pigs were vaccinated at 1 day of age by the intramuscular (n = 10) or intranasal (n = 10) route, or given saline (n = 5). Eighteen weeks later, the pigs were challenged with a PRRSV-1 field strain.

To characterize immune development, study investigators took blood samples at several points after vaccination and after challenge to measure levels of various immune molecules, known as cytokines, that are associated with the innate and adaptive arms of the immune system. The innate immune system is non-specific and provides animals with their earliest form of immune protection, Balasch explained. Meanwhile, the adaptive immune system — consisting of humoral and cell-mediated components - targets specific antigens and develops later in life.

Cytokines measured in the study included IL-8, IL-10, TNF-a and IFN-a. IFN-g-secreting cells and neutralizing antibodies (NA) to the vaccine strain were also measured.

Results

Results from the vaccinated pigs demonstrated:

• Undetectable or low levels of pro-inflammatory cytokines IL-8 and TNF-a. Inflammation can be harmful to young pigs, so this finding reinforces the strong safety profile of the vaccine.
• No production of IL-10, a cytokine that is known to interfere with innate immune response.
• Consistent induction of IFN-a- and IFN-g-secreting cells. The presence of these cytokines following vaccination predicts the development of robust cell-mediated immune response later in life.
• Induction of NA to the vaccine strain, an indicator of humoral immune response. After PRRSV challenge, there was a rapid boost in NA, indicating a priming effect of the vaccine.

Based on these findings, investigators concluded that piglets vaccinated at 1 day of age can develop innate, humoral and cell-mediated immune responses to the vaccine strain very early that are sufficient to protect them from an experimental challenge with a wild-type PRRSV strain.

A paradox and a ‘plus’

According to Balasch, the ability to safely and effectively vaccinate pigs on day 1 is both a paradox and a “plus” when it comes to PRRSV protection.

“It’s a paradox because day-old pigs generally have a reduced ability to respond to immunological stimulation compared to pigs of weaning age,” she noted.

“However, that was not the case with the vaccine used in our study. Despite the immaturity of their immune systems, the pigs vaccinated on day 1 were still able to mount an immune response that was adequate to clear the challenge virus when infected.”

The ability to vaccinate pigs at 1 day of age, rather than at weaning, has meaningful benefits, Balasch added.

“By vaccinating pigs on day 1, producers can ensure the pigs are protected at weaning, helping to close the gap between the loss of maternal immunity - usually around 3 to 4 weeks of age - and the onset of active immunity, 3 to 4 weeks after vaccination,” she explained.

“The earlier onset of protection we see with this live PRRSV vaccine, combined with the robust innate, humoral and cell-mediated responses we observed in our study, make it a reliable insurance policy against PRRSV as well as the costly secondary infections and production losses that are associated with it.”

To view the full study, click here.