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Experts Consider 4-Strain Flu Vaccine to Fight B Viruses

January 16, 2009
by Robert Roos
CIDRAP

Picking the influenza strains to put in the flu vaccine each year is always a gamble, given the unpredictable prevalence of different strains, but choosing the influenza B strain has become particularly vexing in recent years.

Since the 2001-02 flu season, two distinct lineages of influenza B-Victoria and Yamagata-have been circulating in the United States, and experts have found it impossible to predict which one would dominate in any winter.

Because a vaccine against one lineage offers little protection against the other, the government's flu vaccine advisors have been discussing for several years the possibility of putting both lineages in the seasonal vaccine. That would turn the standard three-strain, or trivalent, vaccine into a quadrivalent vaccine. Trivalent vaccine contains two subtypes of influenza A-H3N2 and H1N1-and one of influenza B.

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