The currently available commercial PCV2 vaccines include two subunit vaccines based on the PCV2 capsid protein expressed in the baculovirus system and an inactivated vaccine based on a PCV2 virus (9). All of these vaccines are based on the PCV2a CP-673451 cost subtype,

which several studies have shown to be cross-protective against PCV2b challenge (35, 36). An experimental live chimeric vaccine was generated with the idea that it might provide more broad cross protection and better immunity, and could be adapted for use by the oral route. The experimental chimeric PCV2 vaccine was developed by replacing the ORF2 of PCV1 with the ORF2 of PCV2a in the genomic backbone of the non-pathogenic PCV1 (37). An inactivated version of the chimeric PCV2 vaccine, which was known under JQ1 chemical structure the trade name Suvaxyn PCV2 (Fort Dodge Animal Health, Overland Park, KS, USA) and developed and licensed for pigs 3 weeks of age and older, became commercially available in 2006 (9). It was later voluntarily removed from the market but was then reintroduced in August 2011 in a reformulated version under a new name: Fostera PCV (Pfizer Animal Health, Madison, NJ, USA). Previous studies using the experimental live attenuated PCV2 vaccine demonstrated no evidence of reversion of

the live attenuated PCV1-2 to its parental wild-type viruses (PCV1 or PCV2) after 11 serial passages in PK-15 cells and the PCV1-2 was found

to be genetically stable during three serial passages in pigs (38). In addition, the experimental live chimeric PCV2 vaccine was shown to be attenuated in pigs and to induce strong protective immunity in the PCV2a HSP90 challenge model (39) and in a triple challenge model (40). Recently, the vaccine efficacy of IM administration of the live-attenuated chimeric PCV2 experimental vaccine based on subtype PCV2a was tested in a triple challenge model using PCV2b, PPV and PRRSV (41). In conventional pigs with variable amounts of anti-PCV2 antibodies and degrees of PCV2 viremia at the time of vaccination, the live-attenuated chimeric PCV2 vaccine was found to reduce the amount of PCV2 DNA in serum compared to non-vaccinated challenged pigs (41). In addition to the chimeric PCV2 vaccine based on PCV2a, a novel chimeric PCV2 virus with the PCV2b capsid gene cloned into the backbone of PCV1 was recently described (42). In a single challenge model in SPF pigs using a PCV2a or PCV2b challenge, IM administered attenuated live chimeric PCV2b vaccine was found to decrease lymphoid lesions and to prevent detectable PCV2 viremia (42). The efficacy of the live-attenuated chimeric PCV2b vaccine administered by combined IM and intranasal routes was also evaluated in a PCV2b-PRRSV-PPV triple challenge model and found to induce protective immunity in SPF pigs (40).