Antigenic stability of H1N1 pandemic vaccines correlates with vaccine strain

In 2009 a novel H1N1 influenza virus emerged and spread rapidly. Soon after vaccine lots were released, however, the shelf life was revised downward due to an unexpected decrease in HA potency. In this study, we found differences in both stability and antigenic content of two monovalent H1N1/2009 vaccine preparations. These appear to have arisen due to differences in the A/California/7/2009-like influenza strain used to prepare vaccine.