Table 2.

Comparison of Antibody Responses to Tetanus and Diphtheria According to Age^a

Age Group, y	DT Ab Titer, Mean (SD), IU/mL	DT Ab Half-life (95% CI), y		TT Ab Titer, Mean (SD), IU/mL	TT Ab Half-life (95% CI), y
		Cross-sectional	Longitudinal		Cross-sectional	Longitudinal
<50	0.43 (0.70)	24 (12–∞)	19 (15–25)	4.16 (5.41)	11 (8–20)	11 (10–13)
≥50	0.28 (0.48)	30 (18–84)	21 (15–34)	3.05 (3.62)	14 (11–20)	15 (11–24)

Abbreviations: Ab, antibody; CI, confidence interval; DT, diphtheria toxin; SD, standard deviation; TT, tetanus toxin.

^a Antibody titers to DT or TT were determined after stratifying the cohort of 540 subjects of known age into age groups of <50 or ≥50 years (both n = 270). Antibody half-life estimates (in years) were determined after stratifying 388 subjects of known age and estimated time after vaccination into age groups of <50 (n = 177) or ≥50 (n = 211) years. Longitudinal data [7] were stratified by age for comparison with the cross-sectional analysis.