1 April 2025

4 minute read

By: Zoetis

Key takeaways

• Vaccination is one of the key approaches to control porcine reproductive and respiratory syndrome (PRRS).

• To be effective, a PRRS vaccine does not have to be from the same lineage as circulating PRRS virus strains.

• Fostera® PRRS, a Lineage 8 vaccine, is just as effective as a Lineage 1 vaccine in pigs challenged with a Lineage 1 field strain of the PRRS virus.³

Porcine reproductive and respiratory syndrome (PRRS) has been described as one of the most prevalent swine diseases of the last half-century with costs increasing 80% since 2010 to an estimated $1.2 billion per year.¹ As costs continue to add up for producers, being proactive and choosing the right vaccine strategy for your operation makes a difference for herd health and economic success.

Challenge studies produce results.

When determining the best approach, it’s important to evaluate PRRS vaccine efficacy and understand that a vaccine does not need to be from the same lineage as circulating herd PRRS virus strains.

“The PRRS virus is genetically diverse, and it has a relatively high rate of mutation and recombination. That’s why it’s important to select a vaccine that cross-protects against different strains of the PRRS virus,” says Micah Jansen, DVM, Managing Pork Technical Services Veterinarian, Zoetis U.S. Pork.

As evidence, Jansen cites a recent challenge study that compared the effectiveness of 2 PRRS modified live virus (MLV) vaccines, one a Lineage 8 strain and one a Lineage 1 strain. The challenge was with a 1-7-4 strain, which first emerged in North Carolina and has caused up to 50% mortality in growing pigs.²

Pigs were vaccinated at 2 weeks of age and received either Fostera PRRS (Lineage 8 MLV), a Lineage 1 PRRS MLV vaccine, or saline (unvaccinated controls).³ Pigs were challenged intranasally and intramuscularly four weeks later with the 1-7-4 strain, says Jansen.

Pigs in both vaccinated groups had fewer lung lesions and higher average daily gain (Figure 1) compared to unvaccinated, challenged controls. However, pigs in the Lineage 8 vaccine group (Fostera PRRS) had less viremia than pigs that received the Lineage 1 vaccine, and at times, the difference was significant (Figure 2), she says, noting that viremia reflects the severity and advancement of PRRS virus infection.³

Notes: Arithmetic means are presented for Days 7 and 28 as treatments were not yet commingled.

“Fostera PRRS was just as effective against a Lineage 1 PRRS virus challenge as the Lineage 1 vaccine,” Jansen says.³

Improve performance with a high-performance vaccine.

Vaccination is one of the key approaches to PRRS control. Although MLVs do not provide sterilizing immunity — immunity that prevents infection — they can reduce clinical signs, reduce viral shedding and improve overall performance.

In a 2005 study conducted at Iowa State University, pigs were immunized with an MLV for PRRS and then challenged with PRRS virus isolates that were only between 76-89% similar to the vaccine strain. The vaccine was still highly effective in reducing the severity of PRRS virus associated disease and lesions. In fact, the greatest reduction in lung lesions occurred in pigs vaccinated with strains that had less similarity, or less homology, with the vaccine strain. This is further proof that the degree of genetic homology between MLV PRRS virus vaccine and the infecting strain is not a good predictor of vaccine efficacy.⁴

What’s the difference and why it matters.

Jansen explains that the PRRS virus is classified into 9 lineages. A PRRS vaccine that’s based on the same lineage group as a PRRS wild strain is said to be homologous, or similar, to the circulating strain. When the lineage of a PRRS vaccine and wild strain differ, the vaccine is said to be heterologous to the circulating strain.

“We’ve known for over a decade that a PRRS vaccine does not have to be homologous to wild strains to be effective and that homology is no guarantee that a vaccine will be more effective against a circulating PRRS strain,” she says.

Conclusion

“In the end, it’s all about pig performance — that’s what affects a producer’s return on investment,” Jansen says. Knowing the lineage of the PRRS virus in your vaccine is helpful, but challenge studies demonstrate performance on the farm. A robust vaccine like Fostera PRRS, which has demonstrated protection against a variety of strains, sets your herd health strategy up for success.