Figure 5. Geometric mean titers of anti-influenza A(H1N1)2009 virus antibodies among pandemic influenza-vaccinated individuals.

The serum samples from persons vaccinated with one dose of pandemic influenza A(H1N1)2009 virus vaccine were collected on day 0 (black dots), on day 21 (open circles), and one year after the vaccination (grey triangles) and analyzed by HI test with viruses detected in Finland during influenza seasons 2009–10 (A) and 2010–11 (B). Geometric mean titers (+/− 95% CI) for each virus were calculated. The significance of differences between the egg-grown vaccine virus A/California/07/2009 (Cal E2)-specific antibody responses and multiple Finnish pandemic virus isolates were calculated using Student's t-test, * p<0.01, ** p<0.001, *** p<0.0001.