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(a) Overall antibody reactivity against different antigens for the entire study period (week 40, 2008 to week 34, 2010) including all countries. (b) Development of A(H1N1)pdm09 over time for all countries combined. Pandemic onset and -course per country were previously described in de Bruin et al.30. Both y-axes represent fluorescence values on a log10-scale.
