Cross-strain influenza A(H1N1) antibody responses measured by HI assay.*

HI = hemagglutination inhibition; TIV = trivalent inactivated influenza vaccine. Note that undetectable titres *Unit of analysis pooled sera from 5 mice, thus 10 pools from 50 mice were available for this experiment.aMeasured two weeks after specified TIV dose;bMeasured two months after specified TIV dose.†Compared to pre-immunization for initiating antigens; compared to immediately preceding titre for boosting antigens.Brisbane = A/Brisbane/59/2007(H1N1)-like, component of the northern hemisphere 2008–09 and 2009–10 TIV.California = A/California/07/2009(H1N1)-like, component of the northern hemisphere 2010–11 TIV.