Porcine Circovirus 2 (PCV2) vaccines are poorly standardized in terms of antigen payload and correlates of protection. Therefore, twenty, 45-day old piglets were divided into four groups of 5 animals each and vaccinated with 800 / 266 / 88 / 0 nanograms, respectively, of an inactivated PCV2b strain formulated in the same oil adjuvant. Twenty-six days later, all the pigs were challenged intranasally with the homologous PCV2b strain. No clinical signs were observed in the pigs under study. Viremia was observed after challenge in all the control pigs, as well as in 3 pigs of the 266 and 88-ng groups (one and two, respectively). No pigs of the 800-ng group developed viremia. On the basis of post challenge viremia, the PCV2b vaccine under study had a titer of 11 Protective Doses (PD) 50 %, and 1 PD₅₀ amounted to 74 ng of PCV2b Ag. Neutralizing and ELISA Ab titers showed no obvious correlation with protection in the single animals, even though the 800-ng group developed a significantly higher mean Ab response. All the pigs with a PCV2-specific, IFN-gamma response at 3 weeks after vaccination in whole blood samples were protected against viremia. In lymphoid tissues (mainly tonsils and ileum) the presence of sparse reactive histiocytes and multinucleated giant cells was the only PCV2-associated feature and, by immunohistochemistry, only 3 out of 20 subjects showed a low viral load.

猪圆环病毒2（PCV2）疫苗在抗原有效载荷和保护相关性方面标准化不佳。因此，将20只45天大的仔猪分为四组，每组5只动物，分别接种800/266/88/0纳克在同一油佐剂中配制的灭活PCV2b菌株。二十六天后，用同源PCV2b株鼻内攻击所有的猪。在研究中的猪中未观察到临床症状。攻击后在所有对照猪以及266和88-ng组的3只猪中分别观察到病毒血症（分别为一和二）。800 ng组的猪均未出现病毒血症。根据激发后病毒血症，所研究的PCV2b疫苗的效价为11保护剂量（PD）50％，1 PD ₅₀达到74 ng PCV2b Ag。中和和ELISA Ab滴度与单只动物的保护没有明显的相关性，即使800 ng组的平均Ab应答显着更高。在全血样本中接种疫苗后第3周，所有具有PCV2特异性IFN-γ反应的猪都受到了病毒血症的保护。在淋巴组织（主要是扁桃体和回肠）中，稀疏的反应性组织细胞和多核巨细胞的存在是与PCV2相关的唯一特征，并且通过免疫组织化学，在20名受试者中只有3名表现出低病毒载量。