Reid Philips, Technical Manager for PRRS with Boehringer Ingelheim, speaks to ThePigSite's Sarah Mikesell at the North American PRRS Symposium about the role of vaccine-derived immunity.

A high percentage of the cost incurred due to PRRS in the North American swine industry is in the growing pig population, said Reid Philips, Technical Manager for PRRS with Boehringer Ingelheim.

"As we measure average daily gain (ADG) or reductions in ADG and mortalities, the cost of PRRS is pretty high and it's where a lot of the virus reservoirs," he said. "We want to control the virus, improve health and performance, but we also want to reduce the amount of virus circulation in growing pigs - a two-pronged approach."

With the appropriate vaccination protocols, the role of vaccine-derived immunity can accomplish both through a direct benefit and an indirect benefit.

"The direct benefit of vaccine-derived immunity is vaccinated pigs for protection against the virus should they get exposed to infection. It will mitigate the consequences of infection, improve health and performance as measured by ADG and reduction in mortality," Dr. Philips said. "It's what every producer wants, and it's a good return on his investment."

The indirect benefit of vaccine-derived immunity is a reduction in the amount of virus shed and spread within and between vaccinated populations.

"This is very important because at the end of the day, we want to improve health and performance, but we want to minimize, mitigate, if not even eliminate the amount of virus that's circulating in these large growing pig populations," he said.

This ultimately reduces the risk of disease transmission. Along with other complementary management practices like biosecurity and adequate pig flow, herd immunity can help move the needle in a holistic approach to control PRRS in the industry.

"Reinfection occurs when the virus is introduced one way or another into a stable or a naïve population," he said. "To mitigate that, we just have to reduce the amount of virus that's circulating in infected populations and immunity matters."