Comparison of Monovalent and Trivalent Live Attenuated Influenza Vaccines in Young Children

Abstract

Fifty children, 6 months to 2 years of age, were vaccinated intranasally with a trivalent preparation containing 10⁶ TCID₅₀ each of H1N1 and H3N2 and 10⁴ (n = 14) or 10⁶ (n = 36) TCIDso of B live, attenuated, cold-adapted (ca) influenza strains. The same doses were administered as monovalent vaccines to 69 comparably aged children. Forty-five controls were given placebo. No clinically significant adverse reactions to vaccines were observed. Of children seronegative to HINI or H3N2, ⩾90% were infected by these vaccine strains. Trivalent vaccine containing 104 TCID₅₀ of B infected only 27% of children seronegative to B (3/11), which was markedly reduced from the 88% infection rate (7/8) following monovalent B vaccine of the same dose (P = .02); increasing the B dose to 10⁶ TCID⁵⁰ increased the infection rate to 81% (21/26). Replication of ca influenza viruses in tissue culture matched vaccine responses. Trivalent ca influenza vaccines can be formulated that are safe and immunogenic in young children.