Figure 2

Number of study subjects with influenza-like illness and laboratory-confirmed 2009 pandemic influenza A (H1N1) infections were plotted over an epidemic curve of confirmed 2009 pandemic influenza A (H1N1) cases in Taiwan. The first epidemic wave began in late August and ended in September 2009; the second occurred between mid October 2009 and February 2010. Gray boxes indicate first, second, and third blood sampling periods. Hollow arrows indicate when a nationwide vaccination with monovalent 2009 pandemic influenza A (H1N1) vaccine was implemented.