Correlation coefficiencies of the antibody titers between different virus isolates used in the HI test.

The Pearson product moment correlation coefficients (r) were calculated for all pairs for 2009–10 viruses (panel A) and for 2010–11 viruses (panel B). All correlation coefficients were significant (p<0.01). C) The scatter plots and trend lines of antibody titers for each Finnish A(H1N1)2009 virus compared to the A/California/07/2009 vaccine virus.