IgM and IgG antibody responses following immunization of children and adults with influenza A/NJ/76 vaccines.

The character of the immune response to inactivated monovalent influenza A/New Jersey/76 (A/NJ/76) and bivalent influenza A/New Jersey/76-A/Victoria/75 (A/NJ/76-A/Vic/75) vaccines was studied in children 6 months to 18 years of age. Hemagglutination-inhibiting antibody levels were measured in post-vaccination serums before and after 2-mercaptoethanol treatment. IgG antibody predominated in responses to the influenza A/Vic/75 component of bivalent vaccines. In contrast, specific IgM antibody against influenza A/NJ/76 developed after both monovalent and bivalent vaccines, and appears to characterize the immune response to this antigenic "shift" strain in children. Prevalences of IgM antibody against influenza A/NJ/76 did not differ significantly by age, implying that type rather than extent of previous influenza experience determines the IgM antibody response to an antigenic "shift". Slit-product vaccines produced significantly fewer IgM antibody responses to influenza A/NJ/76 than did whole-virus vaccines, a phenomenon which may correlate with their diminished reactogenicity and immunogenicity in children.