ABSTRACT
Objective To analyze the genetic stability of master virus seed lots of live attenuated influenza vaccineA/17/California/2009/38(H1N1)andA/17/Perth/09/87(H3N2)strains.Methods The master virus seed lots were inoculated into chicken eggs for subculture.The complete genome of the 2nd, 3rd, 5th and 10th generations of viruses were amplified and sequenced.The genes encoding hemagglu-tinin ( HA) and neuraminidase ( NA) were compared with those of the WHO recommended circulating wild-type virus strains used for vaccine production in northern hemisphere during 2011-2012 influenza season.Six internal genes (PB2, PB1, PA, NP, M and NS) of each virus generation were compared with their master donor virus strain (A/Leningrad/134/17/57) for the evaluation of the genetic stability.Results The muta-tion rates of H1N1 and H3N2 strains after 10 passages were 0.035%and 0.022%, respectively.No muta-tions were found at the critical sites for controling thecold adapted ( ca) , temperature sensitive ( ts) and at-tenuated ( att) phenotypes.Conclusion The live attenuated influenza vaccine strains possessed high genet-ic stability as their tenth generations still shared 99% of homology with the original seed lots.All of the working virus seed lots met the requirements of Pharmacopoeia of the People′s Republic of China ( 2010 edition) .