Influence of age on the effectiveness of PCV2 vaccination in piglets with high levels of maternally derived antibodies

Two field studies were conducted to investigate the influence of age on the efficacy of vaccination against Porcine Circovirus Diseases (PCVD) in animals with high levels of maternally derived antibodies (MDA). A total of 416 piglets (Study 1) and 600 piglets (Study 2) were randomly allocated to one of three groups. Two groups in each study received a single dose of a PCV2 subunit vaccine, one group at 1 week old and the other at 3 weeks of age. The third group was left untreated. Animals vaccinated at 3 weeks of age showed a significantly higher average daily weight gain and significantly reduced viraemia following PCV2 infection than the respective control groups. This difference was not observed in pigs vaccinated at 1 week of age. Furthermore, only animals vaccinated at 3 weeks of age showed an increased serological response and a higher frequency of IgM-positive animals compared with controls. The data indicated that PCV2 vaccination in the presence of high MDA levels is efficacious when used in 3-week old but not in 1-week old pigs. As the range of MDA titres of pigs vaccinated at both 1 and 3 weeks of age were comparable, the data suggest that PCV2 vaccine efficacy was independent of the level of MDA. It appears that other age-related factors affecting the active and passive transfer of immunity may perhaps have interfered with the efficacy of the vaccine in 1-week old piglets. These findings have implications for future PCV2 vaccine testing and administration strategies.     

A live-attenuated and an inactivated chimeric porcine circovirus (PCV)1-2 vaccine are both effective at inducing a humoral immune response and reducing PCV2 viremia and intrauterine infection in female swine of breeding age

The objective of this pilot study was to determine the efficacy of inactivated (1 or 2 dose) and live-attenuated chimeric porcine circovirus (PCV)1-2 vaccines in sows using the PCV2-spiked semen model. Thirty-five sows were randomly divided into 6 groups: negative and positive controls, 1 dose inactivated PCV1-2 vaccine challenged (1-VAC-PCV2), 2 dose inactivated PCV1-2 vaccine challenged (2-VAC-PCV2), 1 dose live-attenuated PCV1-2 vaccine unchallenged (1-LIVE-VAC), and 1 dose live-attenuated PCV1-2 vaccine challenged (1-LIVE-VAC-PCV2). The inactivated PCV1-2 vaccine induced higher levels of PCV2-specific antibodies in dams. All vaccination strategies provided good protection against PCV2 viremia in dams, whereas the majority of the unvaccinated sows were viremic. Four of the 35 dams became pregnant: a negative control, a positive control, a 2-VAC-PCV2 sow, and a 1-LIVE-VAC-PCV2 sow. The PCV2 DNA was detected in 100%, 67%, and 29% of the fetuses obtained from the positive control, inactivated vaccinated, or live-attenuated vaccinated dams, respectively. The PCV2 antigen in hearts was only detectable in the positive control litter (23% of the fetuses). The PCV1-2 DNA was detected in 29% of the fetuses in the litter from the 1-LIVE-VAC-PCV2 dam. Under the conditions of this pilot study, both vaccines protected against PCV2 viremia in breeding age animals; however, vertical transmission was not prevented.