Trials in man with live recombinants made from A/PR/8/34 (H0 N1) and wild H3 N2 influenza viruses.

A long-term study is described of recombinant influenza viruses produced from the avirulent laboratory strain, A/PR/8/34 (H0 N1), and newly isolated H3 N2 influenza virus variants. A number of H3 H2 recombinants were found to be attenuated for man and capable of inducing antibody formation, and were therefore potentially usable as live vaccines. However, the volunteer trials as a whole suggested that, in this system, there might not be complete segregation of virulence and antigenic characteristics. No H3 N2 recombinants were detected which were non-infective for man, like the A/PR8 (H0 N1) parent, and reciprocal hybrids (H3 N1 and H0 N2) always reflected some of the virulence of the parent from which they had inherited their haemagglutinin. This property is not a feature of mouse influenza.