Influenza B Virus Vaccines in Children and Adults: Adverse Reactions, Immune Response, and Observations in the Field

A double-blind trial of influenza virus vaccines was initiated in the fall of 1976. One dose of 500 chick cell-agglutinating units of subvirion influenza B vaccine gave negligible adverse reactions in schoolchildren and young adults, whereas whole-virus vaccine caused systemic reactions. Subvirion vaccines induced a complement-fixing antibody response, particularly in children, that returned to near original levels over a two-year period. Levels of hemagglutination-inhibiting (HAI) antibodies induced by the vaccine remained elevated for at least 2.5 years in the absence of natural challenge. When a major epidemic of influenza B occurred in the winter of 1979-1980, the youngest children (originally six to nine years of age) had the highest infection rate (53%); in this group protection was estimated at 44% +/- 17% by serologic evidence of infection. Little vaccine efficacy was demonstrated in older age groups at three years after vaccination, despite the persistence of HAI antibodies induced by the vaccine.