Heterologous protection in PRRS vaccination

New post in prrscontrol.com. 

Despite the fact that live attenuated vaccines have demonstrated their efficacy both under experimental conditions and in field trials, their capacity to confer cross-protection against heterologous PRRSV strains is still one of the main concerns for swine farmers and veterinarians.

Unfortunately, homology between field virus and vaccine strain is not predictive for the vaccine’s efficacy. However, UNISTRAIN® PRRS has demonstrated clinical protection against both genotype I and II highly pathogenic PRRS challenges. Thus, heterologous protection provided by UNISTRAIN® PRRS is a key point for the control of PRRS in pigs.
One hallmark of PRRS in pigs is the extremely high genetic diversity of the virus. Immune cross-protection of commercial vaccines against this wide range of different PRRS field strains is one of the most controversial and widely-discussed issues between farmers, swine practitioner veterinarians and academic researchers.
According to different studies vaccine efficacy cannot be predicted by PRRS virus strain homology between vaccine and virus infection1 and 2. Despite the fact that mechanisms of immunogenicity and development of clinical protection through PRRS vaccines have not been clearly elucidated yet, some commercial vaccines have shown different degrees of heterologous protection even against field strains of different genotypes. The specific ability of the virus used in immunization to induce cellular immunity could be an important factor for heterologous protection.
VP-046-BIS PRRS strain, the vaccine virus of UNISTRAIN PRRS, has demonstrated a strong cellular heterologous immunogenicity both when it is administered via intramuscular route and intradermally. At the same time, UNISTRAIN PRRS has demonstrated partial clinical protection against highly pathogenic PRRS in pigs of genotype I subtype 3.
Moreover, VP-046-BIS PRRs strain also showed field clinical protection against genotype II PRRS virus infection and against highly pathogenic Chinese-like PRRS virus under experimental conditions3.
Although PRRS vaccines cannot provide full and universal protection against PRRS virus infection, using a vaccine with a wide heterologous clinical protection against multiple field virus strains from both genotypes is a key point for the control of PRRS in pigs.
1. Opriessnig T. et al., 2005. Journal of Swine Health and Production. 13(5): 246-53. 

2. Prieto C. et al., 2008. Veterinary Journal. 175(3): 356-63.

3. Roca M. et al., 2012. Veterinary Journal. 193(1): 92-6.


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