Flu Season Dynamics

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Science  24 May 2002:
Vol. 296, Issue 5572, pp. 1367
DOI: 10.1126/science.296.5572.1367d

The gradual mutation of the hemagglutinin surface protein of influenza A produces immunologically distinct strains (drift variants). If you survive an influenza infection, you gain lasting immunity to that drift variant, but within a few years you become susceptible to influenza again as new drift variants arise. Hence, vaccines have to be updated to be useful.

An expanding database of sequences allows for the reconstruction of hemagglutinin evolution, and the resulting phylogenies show how the most immunogenic part of the molecule, HA1, periodically accumulates the kind of mutations that will cause amino acid changes. This clustering effect suggests that HA1 is under strong Darwinian selection, and the clusters can be used to predict where a phylogentic branch point may emerge, signaling a new lineage. Plotkin et al. have developed a computational technique, complementary to phylogenetic techniques, to predict the course of influenza evolution and thereby offer a tool for updating vaccines. — CA

Proc. Natl. Acad. Sci. U.S.A.99, 6263 (2002).

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