Fig 3

Diphtheria-specific Abs measured by ELISA and neutralizing assay. The concentrations of diphtheria-specific Abs measured by ELISA are shown in correlation to the highest plasma dilution factor able to neutralize diphtheria toxin (8 ng/ml). Diphtheria-specific Abs were compared in samples taken before (day 0_2010), 4 weeks after (day 28_2010) as well as 5 years after (2015) the booster shot. Elderly adults (n = 27) are represented by empty diamonds and solid trend-lines, young adults (n = 17) by filled dots and dashed trend-lines. Spearman rank correlation was applied and correlation coefficients and p-values were determined