Laboratory and clinical characteristics of attenuated strains of influenza virus

摘要: Prior to 1967, attenuation of influenza virus was achieved by gradually lowering the incubation temperature until optimal growth at 25 degrees C obtained. The process a Hong Kong strain modified and considerably shortened. changed abruptly from 35 cold variant selected using plaque-assay system.A set genetic markers developed for assessing potential virulence cold-passaged variants. temperature-sensitive, acid-labile produced small plaque in primary chick kidney cells incubated C. Additional differentiating biological properties relating adaptation loss susceptible host are presented.The cold-adapted found be relatively avirulent highly antigenic mice ferrets, recovered nasopharynx infected ferrets during first 3 days. still unable grow well 41 (rct/41-), sensitive acid pH plaques larger ones C.After series purifications, showed further mice, more vigorous C, complete failure good potency.The were stable plaque-purified after least 10 consecutive passages either tissue culture or mice.Cold variants type B have narrower range sensitivity compared with A strains. Reduced plaquing efficiency reproductive capacity occurred (rct/35-) attenuated strains instead as strains.Clinical trials (A2/Aichi/2/68) demonstrated acceptability immunogenicity man.