RECENT INFLUENZA-B VIRUSES IN EUROPE - A PHYLOGENETIC ANALYSIS

Background: Influenza B virus evolution is currently in a unique situa tion having two cocirculating main lineages B/Yamagata/16/88 (YM/88)-l ike and B/Victoria/2/87 (VI/87)-like viruses. Continuation of this bif urcation would mean development towards distinct forms resembling the HA subtypes of influenza A viruses. Objective: We wanted to examine bo th intraepidemic heterogeneity and recent evolution in these two linea ges. The initial purpose was to determine the geographic distribution of the two sublineages of the VI/87-like viruses in Europe in 1989-199 0 under circumstances of low epidemic activity. Due to the outbreaks o f YM/88-like viruses since 1991, the study was extended to contain the evolution of these viruses and their genetic relationship with the va ccine strains of that time. Study design: The HAI gene sequences of 33 influenza B strains isolated in ten European countries since 1989 wer e determined and compared with those available through databases or pe rsonal contacts. Results: The two main lineages, YM/88-like and VI/87- like viruses, both continued to circulate. In both lineages, changes i n the potential glycosylation sites were observed. Two sublineages of the VI/87 lineage cocirculated during the 1989-1990 season with somewh at different geographic distributions. A high degree of intraepidemic heterogeneity was observed, as well as examples of conserved nucleotid e sequences. Conclusions: It is important to follow the evolution and circulation of VI/87-like viruses. Current vaccines give poor or no pr otection against VI/87-like viruses in immunologically unprimed childr en or even in primed adults (Levandowski et al., 1991, Pyhala et al., 1994). Changes in the potential glycosylation pattern in the latest vi rus isolates of both main lineages have occured and it is interesting to see the significance of these changes to viral evolution.