Abstract

Characteristics of avian-human (ab) and cold-adapted (ca) influenza A/Kawasaki/9/86 (H1N1) reassortant vaccine viruses were compared in 37 seronegative adults and 122 seronegative infants and children. The 50% human infectious dose (HID50) in infants and children was 102.9 and 102.6 TCID50 for the ab and ca vaccine, respectively. The ah influenza A/Kawasaki/9/86 reassortant was reactogenic: 24% of infants and children infected with ⩾100 HID50 had fever ⩾39.4°C. Since H3N2 ah vaccines were previously shown to be adequately attenuated, it is reasonable to suggest that the genes that code for hemagglutinin and neuraminidase of the H1N1 virus apparently influence the reactogenicity of reassort antviruses derived from the avian influenza A/Mallard/NewYork/6750/78 donor virus. Because this avian virus does not reproducibly confer a satisfactory level of attenuation to each subtype of influenza A virus, it is not a suitable donor virus for attenuation of wild-typeinfluenza viruses. In contrast, the ca A/AnnArbor/6/60 donor virus reliably confers attenuation characteristics to a variety of H1N1 and H3N2 influenza A viruses.

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