As we have shown FhGST-S1 to have key roles in F. hepatica, both in NEJs and adult worms, coupled with the near surface expression and release of the enzyme via the ES products, we assessed the potential of FhGST-S1 to be used as a vaccine candidate. This was especially poignant given that the S. mansoni Sigma GST homologue (Sm28) is in phase II clinical trials [12] . Unfortunately, the current goat based vaccine trial did not show any significant differences in fluke burdens between the rFhGST-S1 immunised and Quil A control group. However, a high individual variability was recorded, particularly in the vaccinated group also reported in previous trials using goats vaccinated with alternative candidates such as cathepsin L1 [64] and Sm14 [65] . The vaccine trial shown here using a target species with an acceptable adjuvant may have been adversely affected by the strain of F. hepatica used to challenge goats. Here we have shown an unusually high infectivity rate with the strain of F. hepatica used; which we have reported in a previous trial using goats [64] . Using an alternative strain of F. hepatica for experimental infections in this species has given normal infectivity rates ranging from 14% to 26.5% [65] .