IgM and IgG antibody responses after immunization of children with inactivated monovalent (A/New Jersey/76) and bivalent (A/New Jersey/76-A/Victoria/75) influenza virus vaccines.

The character of the immune response to inactivated monovalent influenza A/New Jersey/76 and bivalent influenza A/New Jersey/76-A/Victoria/75 vaccines was studied in children six months to 18 years of age. Titers of hemagglutination-inhibiting antibody in sera taken after vaccination were measured before and after treatment with 2-mercaptoethanol. IgG antibody predominated in responses to the influenza A/Victoria/75 component of bivalent vaccines. In contrast, specific IgM antibody to influenza A/New Jersey/76 virus developed after administration of both monovalent and bivalent vaccines and appeared to characterize the immune response to this antigenic "shift" strain in children. Prevalences of IgM antibody against influenza A/New Jersey/76 virus did not differ significantly by age. This finding implies that type rather than extent of previous experience with influenza determines the IgM antibody response to an antigenic "shifts." Split-product vaccines produced significantly fewer IgM antibody responses to influenza A/New Jersey/76 virus than did whole-virus vaccines, a phenomenon that may correlate with their diminished reactogenicity and immunogenicity in children.