Poster: H3N2 influenza vaccine: A historical perspective

The hemagglutinin protein of H3N2 influenza A virus undergoes rapid evolutionary variation that causes many changes in its antigenic epitopes. Because of these changes, annual vaccine formulation needs to be updated to reflect the changes in order to trigger antibodies neutralizing capability. In this paper, the dN/dS ratios of the vaccine strains against the immuno-escape mutant strain circulatings were analyzed. Result shows that the position of the antigenic sites is shifting to avoid mutation in previously targeted sites by the vaccine. This suggests that the influenza virus shows a first order memory effect from the previous exposure to the antibody immune response. It was also seen that the hypervariability regions are under much larger mutation pressure than the rest of the sequence. Synonymous mutation appears to be closing the gap on the non-synonymous mutation which suggests that synonymous changes may have a major impact on fitness, contrary to a base hypothesis of being selectively neutral.