FIG 4.

Antigenic distance of reference swine N2 to the N2 from human seasonal vaccines. (A) Antigenic distance between swine and human N2 increased over time. The NAI of swine N2 antisera against human seasonal N2 was determined using the ELLA. Antigenic cartography was used to chart the NAI data and calculate antigenic distances. The antigenic map reflects the introduction of human N2 into the U.S. swine population in 1998 and 2002 by A/Wuhan/359/1995-like and A/Fujian/411/2002-like viruses, respectively. (B) Graphical representation of antigenic distances between N2 of selected reference swine and human seasonal vaccine strains. Each contemporary antigen is listed on the x axis, and the distances to reference antigens of the N2-98 lineage (bottom) and N2-02 lineage (top) are represented by colored dots. Bold line indicates an antigenic distance of 3 AU.