I was having exactly this conversation with someone yesterday especially around where you'd draw the line on frequency of boosting and whether the same logic should therefore apply to nobivac too! With filavac, the advice arose because of its origins as a meat rabbit vaccine. The meat farms would batch vaccinate all the rabbits at one point in time, and they were still getting outbreaks in spite of this, hence the original data sheet said duration of immunity 12m but you can boost at 6 months if you like. So it's a bit of a belt and braces approach to ensuring that the rabbit has developed a good immune response, and the chances of them having not received a good immune response are likely in higher stress situations such as breeding, rescues, showing, places with high turnover of rabbits (boarding, rescue) etc. The advice from RWAF is that while it's not ideal, because of the prevalence of these diseases, it's far less risky than under vaccinating.
