OBJECTIVETo characterize HA1 gene of influenza B virus circulated in 1990 through 2000 in China.

METHODSViral RNA was extracted and transcribed into cDNA by reverse transcriptase and amplified by PCR. The product of PCR was purified and sequenced by ABI377. The sequence data were analyzed with epidemic records.

RESULTS1. Two major lineages of influenza B virus always circulated during the period of 1990-2000 in China; the Yamagata lineage was the main lineage, but in 1994 and 1997 the Victoria lineage was more active. 2. During 1992-2000 the Yamagata lineage evolved into two minor groups whose distance in HAI amino acid sequences was about 6%. 3. Large and non-reverse mutators led the development of influenza B epidemics in 1990-2000 in China. 4. Except for a few strains, there was little difference among the influenza B viruses of the same major lineages circulated in the same year in China.

CONCLUSIONSTwo major lineages of influenza B virus always circulated during the period from 1990-2000 in China,and the Yamagata lineage diverged into two minor groups in recent years. Exchanges of the lineages and the appearance of large non-reverse mutators possibly had important epidemic significance.