title: Attenuation of human influenza A viruses.
abstract: The attenuation of two human influenza A viruses has been carried out, using the selection of inhibitor-resistant strains and multiple passages at low temperatures. A virus related to A2/Tokyo/3/67 was obtained in an inhibitor-resistant form. When this was compared with the inhibitor-sensitive strain in a volunteer trial it was relatively non-pathogenic. The second virus, A2/Hongkong/1/68, was subjected to much longer treatment, but nevertheless remained slightly sensitive to serum inhibitor. When given to volunteers it was less pathogenic than before but attenuation was incomplete. A2/Hongkong/1/68 was also modified by passage at low temperatures. Many of these passages are apparently necessary for full attenuation.All attenuated viruses were infective and antigenic.
mesh_terms: D000917:Antibody Formation; D000941:Antigens; D000998:Antiviral Agents; D002986:Clinical Trials as Topic; D003080:Cold Temperature; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007252:Influenza Vaccines; D009975:Orthomyxoviridae / Q000472:pathogenicity*; D014776:Virus Cultivation
chemical_list: D000941:Antigens; D000998:Antiviral Agents; D007252:Influenza Vaccines