Principles Underlying the Development and Use of Live Attenuated Cold-Adapted Influenza A and B Virus Vaccines

BIVALENT INFLUENZA A VIRUSES Generation and characterization of the influenza A/AnnArbor(AA)/6/60 ca donor virus.The influenza A/AA/6/60 (H2N2) ca donor virus was generated by adaptation to replication at low temperature as indicated in Figure 2. The multiple passages at progressively lower temperatures in primary chicken kidney cell (PCKC) culture including biological cloning yielded the A/AA/6/60 ca donor virus that exhibited LIVE ATTENUATED COLD-ADAPTED INFLUENZA A AND B VIRUS VACCINES FIG. 2. Attenuation of the influenza A/AA/6/60 (H2N2) ca donor virus by passage in primary chicken kidney cells (PCKC) at successively lower temperatures (53).The influenza A/AA/6/60 (H2N2) ca donor virus exhibits three phenotypes, that is, the ts, ca, and att phenotypes.E indicates a passage in the allantoic cavity of embryonated chicken eggs.FIG. 5. Derivation of the influenza B/AA/1/66 ca virus by passage at progressively lower temperature in primary chicken kidney cells (PCKC) and by amplification in embryonated chicken eggs (E).