The cocirculation in several parts of the world of influenza viruses B/Yamagata/16/88 and B/Victoria/2/87, which are genetically and antigenically divergent, has prompted the question of whether immunization with one viral antigen is sufficient for protection against both strains. Twenty-three high-risk infants and young children were immunized with a commercial trivalent influenza vaccine containing the antigens of influenza virus B/Yamagata/16/88. When antibodies against influenza viruses B/Yamagata/16/88 and B/Victoria/2/87 were determined, increases developed uniformly to both in the sera of primed children previously exposed to influenza virus B/Victoria/2/87 by immunization or infection. Antibodies against B/Yamagata/16/88 developed in the sera of unprimed children with titers similar to those of the primed children. However, antibodies to B/ Victoria/2/87 were not detected in the sera of the unprimed children. These data suggest that children with out appropriate immunologic priming may not be protected against an infection with a B/Victoria/2/87 strain after vaccination with a B/Yamagata/16/88 strain. Immunization with more than one influenza B virus strain may be desirable in some high-risk pediatric patients if divergent influenza B viruses circulate.
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