Explanations for the Low Effectiveness of the Influenza H3N2 Vaccine

Influenza vaccine strains are selected annually from clinical isolates based on epidemiologic and antigenic properties. However, large-scale production of virus particles for vaccine preparation is usually done in chicken eggs. Adaptation of the virus to growth under these conditions may induce subtle alterations in the hemagglutinin protein (the viral attachment factor) that may affect vaccine antigenicity. Two new studies now confirm the hypothesis that such effect explain the low effectiveness of the H3N2 influenza vaccine component in recent years. Wu and colleagues performed x-ray structural and immunological analysis of the 2007 H3N2 influenza strain and identified a single amino acid substitution that appeared after only a few passag…