Vaccine protection against different PRRS virus strains
Introduction
Porcine reproductive and respiratory syndrome (PRRS) is a complex and costly disease, due in part to the high degree of genetic variation among PRRS virus field isolates. This makes it more difficult to produce vaccines that will protect against many different isolates. Throughout its 25-year history, Ingelvac® PRRS MLV, the No. 1 PRRS vaccine on the market in Canada,1 has demonstrated its ability to provide protection against numerous wild-type PRRS virus strains that differ from the vaccine strain.
Cross-protection against strains of different sequences or lineages
Although it is sometimes assumed that vaccines with similar sequence or lineage origin to current field strains may provide more effective protection, studies have shown this isn’t the case. Ingelvac® PRRS MLV is classified as lineage 5.1. To confirm the vaccine provides effective cross-protection against current and virulent PRRS virus strains of a different lineage, two challenge studies were conducted with PRRS 1-7-4 and 1-3-4 field isolates, both strains within lineage 1.2,3 In both studies, pigs vaccinated with Ingelvac® PRRS MLV showed significantly reduced lung lesions and significantly increased average daily weight gain (ADWG) compared with the placebo group. The results were either numerically or statistically significantly better than those obtained with a competitive vaccine.
Table 1: Efficacy of Ingelvac® PRRS MLV Against PRRS 1-7-4 Challenge: Day 42 Lung Lesions (Median %) and Post-Challenge Average Daily Weight Gain (ADWG)2
Treatment | Lung Lesions (Median %) | ADWG in lbs. |
Ingelvac® PRRS MLV | 8.4a | 0.61a |
Competitive vaccine | 12.9a | 0.49a |
Placebo | 25.4b | 0.24b |
a significantly different from the placebo at P ≤ 0.05.
Table 2: Efficacy of Ingelvac® PRRS MLV Against PRRS 1-3-4 Challenge: Day 42 Lung Lesions (Median %) and Post-Challenge Average Daily Weight Gain (ADWG)3
Treatment | Lung Lesions (Median %) | ADWG in lbs. |
Ingelvac® PRRS MLV | 14.9a | 0.317a |
Competitive vaccine | 27.4a | 0.052c |
Placebo | 58.3b | -0.250b |
Different letters indicate significant (P ≤ 0.05) differences.
Another paper summarized 14 studies conducted by Boehringer Ingelheim that evaluated the efficacy of Ingelvac® PRRS MLV, following challenge with seven genetically diverse PRRS virus isolates that varied by sequence.4 The paper found that Ingelvac® PRRS MLV significantly reduced lung lesions in vaccinated pigs when compared to non-vaccinates. These findings further demonstrate that sequence similarity between virus isolates is an unreliable way to predict cross-protective immunity.5 In addition, the pig challenge model used in these studies is still the gold standard for evaluating the expected level of a vaccine’s cross protection.
Table 3: Lung lesions (%) in pigs vaccinated or not with Ingelvac® PRRS MLV, and challenged with different PRRS virus strains4
Study | Vaccinated | Non-Vaccinated | Challenge isolate |
1 | 1.0 | 31.6 | NADC |
2 | 10.0 | 37.5 | VR 2332 |
3 | 0.7 | 26.0 | 17198-6 (1-4-2) |
4 | 0.3 | 37.7 | SDSU 73 |
5 | 0.6 | 14.8 | 17198-6 (1-4-2) |
6 | 12.0 | 39.9 | MN 1-8-4 |
7 | 10.4 | 36.2 | MN 1-8-4 |
8 | 8.0 | 47.0 | SDSU 73 |
9 | 15.9 | 52.7 | SDSU 73 |
10 | 29.8 | 36.0 | MN 1-8-4 |
11 | 4.5 | 32.9 | MN 1-8-4 |
12 | 1.4 | 18.0 | FI 3 (1-5-2) |
13 | 37.4 | 52.9 | FI 2 (1-4-4) |
14 | 2.4 | 17.6 | MN 1-8-4 |
Isolate Lineages |
NADC – Lineage 5.1 VR2332 – Lineage 5.1 SDSU73 – Lineage 8 17198-6 (1-4-2) – Lineage 9 MN 1-8-4 – Lineage 1 FI 3 (1-5-2) – Not classified based on the analysis FI 2 (1-4-4) – Lineage 1 |
Take home message
- Ingelvac® PRRS MLV has shown efficacy against a multitude of strains with different sequences and lineages.
References
1. Impact Vet, based on 2022 market share and number of doses.
2. Patterson A., Fergan B., Hermann J. et al. Efficacy of Ingelvac® PRRS MLV against a heterologous PRRSV 1-7-4 RFLP challenge. In: Proceedings, AASV 2017; 98-101.
3. Patterson A., Fergan B., Hermann J. et al. Efficacy of Ingelvac® PRRS MLV against a heterologous PRRSV 1-3-4 RFLP challenge. In: Proceedings, Allen D. Leman Swine Conf. 2017; 49.
4. Patterson A., Victoria J., Jordan D., et al. Modified-live PRRSV vaccination is efficacious following challenge with eight genetically diverse PRRSV isolates. In: Proceedings Allen D. Leman Swine Conf. 2013;194.
5. Murtaugh M. Use and interpretation of sequencing in PRRSV control programs. In: Proceedings, Allen D. Leman Swine Conf. 2012;49–55.
Ingelvac® PRRS MLV is a registered trademark of Boehringer Ingelheim Vetmedica GmbH, used under license.
©2023 Boehringer Ingelheim Animal Health Canada Inc. All rights reserved. CA-POR-0012-2023