Recombinant influenza-A viruses as live vaccines for man. Report to the Medical Research Council's Committee on Influenza and other Respiratory Virus Vaccines.

The infection of volunteers with five hybrid influenza-A viruses is described. Four of these were produced in Great Britain by recombining an Ao virus, non-infective for man, with a wild Hong Kong like strain. The fifth was the American recombinant, X-31, derived from similar parents and widely used in the manufacture of killed vaccines. All five viruses had the haemagglutinin and neuraminidase of A2/Hong Kong/68. Two of the viruses were not attenuated and induced symptoms of clinical influenza. The other three were appreciably attenuated and were infective and antigenic. It seems that recombination is a rapid and effective way of producing live vaccine viruses to specification. It is also the quickest known method of attenuation.