Given that the pre-vaccination sera S1 samples were collected over one year post the pH1N1 outbreak (March 2009), some of the vaccinees may have been exposed and seroconverted to the pH1N1 virus before the 2010–2011 influenza season, resulting in the observed bindings of S1 to rH1 and rHA2, as well as rHA1 to a lesser extent. The gene discussed is PSMD1; the disease is influenza.