Even though the first results showed that PMWS vaccination is having a positive effect, we should not forget that PMWS is a multisystem disease, so using a vaccine on its own would not be enough to control the disease (especially on farms that are badly affected). Furthermore, as vaccination does not produce a sterilising immunity, the pathogen is still present on the farm and could potentially cause problems. So vaccination should be accompanied by increased biosecurity and farm hygiene and other good husbandry practices which combat other diseases that are linked to PMWS.
Also, in farms that are low or medium affected, clinical signs are not as obvious, so one might think that the farm is not affected anymore, but there can still be a delay in growth.
Additionally, we should not forget that the vaccine does not go without a cost (currently in England piglet vaccine costs €2.3 per dose).
Finally, we cannot dismiss the possibility that PCV2 could in future mutate and in this situation, the present vaccines will be less or not at all effective.