Use of recombination in the production of influenza vaccine strains.

Recombination between influenza A viruses as a method of producing strains suitable for use in vaccines is discussed with particular reference to a recombination system involving an attentuated laboratory strain A/PR8/34 (HoN1) and a recent isolate of the epidemic strain A/Hong Kong/68 (H3N2). A variety of properties of the viruses were shown to be segregated independently of one another during recombination. These properties included the envelope antigens (haemagglutinin and neuraminidase), growth capacity in the fertile egg and attenuation for man. Some of the recombinants were considered suitable for use in vaccines either inactivated (whole virus particles or subunits) or live. The application of this technique to future requirements for vaccine strains are discussed with particular reference to the safety aspect of using recombinants in live vaccines.