Maternally derived antibodies (MDA) are induced by both the exposure to natural disease and through passive immunity to newborn piglets from active immunization of gilts or sows. These antibodies can interfere with the piglets’ own immune response to vaccines.

MDA interference appears to be possible with all types of vaccines and predominantly affects the antibody response. Immune priming for an anamnestic antibody response, meaning exposure to a second agent leads to an increase in the production of antibodies to the agent of primary exposure, and generation of cell-mediated immunity (CMI), an immune response that does not involve antibodies, may both still occur in conditions where antibody formation is inhibited. However, higher levels of MDA may also suppress priming.

Serological response to PCV2 vaccination

MDA can inhibit serological responses to PCV2 vaccination. However, vaccination can still induce memory and priming for an anamnestic antibody response in conditions where initial production is inhibited by MDA. Having said that, a 2008 study by Opriessnig et al., did find an increase in titer within one week of an experimental challenge in MDA-positive pigs that showed no evidence of a post-vaccination response, although one was seen in MDA-negative pigs.¹ There seems no reason to doubt the fact that B-cell memory for PCV2 can be induced in the presence of MDA interference, and the assumption does not seem to be challenged, even though it is not well-proven in literature.

Although it is assumed that priming can occur under conditions of high MDA, it is still believed that very high levels of MDA might inhibit it, probably because researchers have observed instances where this seems to have occurred. However, no specific study or analysis could be found that conclusively proves the point or identifies a possible threshold.

CMI response to PCV2 vaccination

It is well-established that CMI can play an important role in protection against PCV2, including viral clearance², and that both the capsid and replicase proteins are targets³, which is an important consideration for vaccines that can or are most likely to only stimulate immunity against the former.

Key points to remember about MDA interference⁴:

1. MDA can interfere with serological response to PCV2 vaccination.
2. Establishment of “immunological memory” is less sensitive to MDA interference than primary Ab response.
3. CMI is equally important for PCV2 protection. CMI develops even in the presence of high MDA.
4. PCV2 vaccine appears to be efficacious in conditions of high MDA, including those where a serologic response wasn’t seen.