Clinical reactions and antibody responses to influenza vaccines. A comparison of split or subunit vaccines in children and young adults.

The reactogenicity and immunogenicity of a trivalent split-product influenza vaccine and a trivalent subunit influenza vaccine were studied in 67 children and young adults. Subjects received two doses of either vaccine given one month apart. The reactogenicity of the two vaccines was similar. After the second dose of the split-product vaccine, the prevalence of hemagglutination-inhibiting (HAI) antibody titers of 20 or more was as follows: A/Brazil/78, 73%; A/Bangkok/79, 100%; and B/Singapore/79, 73%. Similar data for the subunit vaccine recipients were 78%, 100%, and 74%, respectively. The HAI antibody responses to the A/Brazil/78 and B/Singapore/79 antigens of both vaccines were relatively poor in those subjects who were initially seronegative (HAI antibody titer less than 5) to the specific antigen.