What is the relevance of present seasonal flue vaccine (2009) in light of the current swine flue pandemic? The present flue vaccine composition was recommended by WHO in anticipation of the prevalent strain expected to circulate in the flue season of this year. Because of the swine flue pandemic, there is confusion regarding predominant prevalent strain at this time.

A unique feature of influenza epidemiology was that once an antigenic variant emerged, it displaced completely the pre-existing strain. Thus, when H1N1 strains arose in 1946-47, they became the only viruses causes human disease, and the previous H0N1 strains disappeared completely. The H1N1 strains were displaced by H2N2 strains in 1957, and they, in turn by H3N2 strains in 1968. But this rule has not been observed in recent years. H3N2 strains continued to be prevalent inspite of pandemics of Hsw1N1 strains in 1976 and H1N1 strains in 1977.

So, at present is there any data/evidence which suggest the co-existence of both the seasonal strain and the pandemic swine flu strain?, or, is swine flu strain is the predominant strain?