Letter to the Editor
Recommendations for PRRS vaccine research
Vaccines are important tools for control and elimination of infectious diseases. Research in pursuit of new and improved vaccines for diseases of veterinary significance needs to build on existing data in order to advance in a timely manner despite limited funding and resources. A particularly relevant example of the problem is porcine reproductive and respiratory syndrome (PRRS) in swine. Vaccine research to develop new PRRS vaccines dominates the funding activities of the National Pork Board PRRS Initiative and the USDA PRRS Coordinated Agricultural Project (PRRS-CAP).
We, the undersigned, are participants in PRRS-CAP. We recommend that publicly funded research and development of PRRS vaccines incorporate, as part of the research plan, a set of common elements that will encourage accelerated analysis and evaluation of ideas and technologies, minimize duplication, and facilitate unbiased scientific evaluation and comparison.
1. All projects must include a challenge experiment. Since the determinants of protective immunity are not known, there is no immunological measurement that can be used to predict vaccine efficacy. Therefore, efficacy must be determined by challenge.
2. Challenge experiments must be performed with a virulent strain substantially different genetically from the vaccine strain. PRRS virus (PRRSV) is genetically diverse, so a vaccine candidate must be able to protect against a wide variety of viral types. Genetic characterization, especially by sequencing of open reading frame 5 (ORF5), is widely accepted for determination of viral diversity and is appropriate for this purpose.
3. The challenge model can be either respiratory disease or reproductive disease or both. The challenge model must produce evidence of infection (ie, viremia) and disease (ie, lung lesions or reproductive abnormalities) in naive control animals. There is no solid evidence that anti-PRRSV immunity is intrinsically different for the two disease manifestations, so use of either model or both models is appropriate for evaluating protection against disease.
4. Challenge studies must include for comparison a positive control consisting of an existing, widely used commercial product. Since the goal of vaccine research is to improve on existing vaccines, an early experiment to assess comparative efficacy will allow earlier decision making so that research can focus on products that indicate a potential benefit over existing products.
Implementation of such requirements would facilitate rapid evaluation of candidate vaccine antigens, delivery technologies, and other immune protection strategies, thus promoting more rapid advancement of methods for the prevention and elimination of PRRS. We also realize that such a strategy would be of value for other animal diseases in which vaccine development or improvement is problematic.
Michael P. Murtaugh
Scott A. Dee
Jeffrey J. Zimmerman
Joan K. Lunney
Robert R. R. Rowland