In this study we have shown that the use of adapted adjuvants can improve the efficacy of a live PRRS
vaccine in pigs while preserving its safety properties (no local reactions and low pyrogenicity). A crucial
information to collect when selecting an adjuvant for a live vaccine model is the compatibility of the
adjuvant with the live vaccine. No viricidal effects could be observed in PRRS live vaccines with either
Montanide Gel 01 PR or Montanide ISA 15A VG. However, pathogen production or attenuation is a
complex mechanism and each antigenic media is unique for its process. Thus, such compatibility studies
should be performed on any new antigenic phase before field trials in order to validate the result.
The main targets of adjuvant addition in live vaccines are the increase of the efficacy of vaccine and
the reduction of the antigenic load per dose in order to reduce costs, reduce risks of reversion and increase
production capacity. We could show that adjuvanted vaccines containing the same antigenic dose as the
unadjuvanted commercial vaccine could significantly improve the resistance to challenge (length of
hyperthermia and lung lesions) despite similar antibody titers compared to the commercial nonadjuvanted
reference. Lung lesions are a good indicator of vaccine performance as they are strongly
linked to the body weight gain of the animals. It should also be noted that the challenge was highly
discriminative for the vaccines (experimental as well as commercial). Indeed, the virulent strain of virus
we used presents 95% of genetic homology to the 2006/2007 Chinese strain which induced more than
40% of mortality in field condition.