How long after pregnancy is the immune system supressed?

Continues thru preg: The immune system continues to work throughout pregnancy but the placenta provides a special separation between mother and child which works most of the time. Rarely, some of the child cells can enter the maternal circulation and cause trouble. More often, a mother's disease or immunization gives the child protection from her disease. Other changes in pregnancy improve many immune diseases.

Not immunosuppressed: There is a misconception that pregnancy causes immunosuppression when in reality there is a change in the immune system, in that it modualtes it's response dependent on the virus/bacteria. So, in reality, pregnancy does not cause immunosuppression, and after pregnancy, the body returns to it's "normal" way to react to pathogens.