Influenza B in the Spring of 1965

Abstract

Summary Strains of influenza B virus recovered from children who had acute respiratory illnesses during the spring of 1965 showed antigenic deviation from the B/Md/ 1/59 strain of influenza virus. This finding was most evident in comparative hemagglu-tination-inhibition tests with chicken antisera but was also shown in the relatively poor antibody response against 1965 B strains compared with homologous virus in children who were given 3 doses of a heptavalent respiratory virus vaccine containing B/Md/1/59 antigen. Further evidence was given in the demonstration of less than expected efficacy of the vaccine in protecting children against influenza B in 1965 in a controlled field study. Sera from normal adults collected in June of 1965 often showed low antibody titers and this was consistent with the sporadic occurrence of influenza B which was recorded in the U.S.A. during the 1964-65 respiratory disease season. The findings in the study may be of value as a guideline for judging the significance of future antigenic deviation of influenza B viruses. The 1965 influenza B viruses were unique in being sensitive to a nonspecific inhibitor in chicken and human sera which was “created” by treatment with periodate. This finding emphasized the importance of establishing the utility, with each virus, of the methods used to remove nonspecific inhibitors prior to their routine application.