Clinical reactions and serologic responses after vaccination with whole-virus or split-virus influenza vaccines in children aged 6 to 36 months.

The reactogenicity and immunogenicity of whole-virus and split-product influenza vaccines were studied in 77 children between the ages of 6 and 36 months. Subjects initially received monovalent vaccine containing either A/USSR/77 (H1N1) antigen in 1978 or A/Brazil/78 (H1N1) antigen in 1979. One month later a trivalent preparation was given which contained the respective H1N1 antigen plus A/Texas/77 (H3N2) and B/Hong Kong/72 antigens. Temperatures of greater than or equal to 37.8 C (greater than or equal to 100 F) were observed more commonly after initial vaccination with whole-virus vaccine (35%) than after split-product vaccine (14%). No child had a temperature of greater than or equal to 39.4 C (103 F) or a febrile convulsion. The trivalent vaccines were more reactogenic than the monovalent vaccines although none of the reaction indices exceeded 0.9. The whole-virus vaccine appeared to be more immunogenic, especially in those children who were initially seronegative (preimmunization hemagglutination-inhibiting antibody titer (less than 5). Only 50% of children vaccinated with split-product vaccines with initial hemagglutination-inhibiting titers of less than 5 achieved titers of greater than or equal to 20 to the H1N1 antigen after two doses of vaccine compared with 97% in similar whole-virus vaccine recipients. The degree of antibody response to the A/Texas/77 component of the vaccines was greater than the response to the A/Brazil/78 or A/USSR/77 antigens.