I believe the difference is that the secondary response is faster and produces more antibodies than the primary response. The primary immune response of the body to antigen occurs on the first occasion it is encountered, following this first exposure to a foreign antigen, a lag phase occurs in which no antibody is produced, but activated B cells are differentiating into plasma cells.The secondary response mediated by B cells with the help of T cells, produces high affinity and antigen specific antibodies.