Table 5. Geometric Mean Concentrations (GMCs) of Tetanus Toxoid (TT) Specific Immunoglobulin G (IgG) prior to (T0) and 1 Month (T1) and 1 Year (T2) after the Meningococcal Serogroup C Tetanus Toxoid Conjugate Booster.

			Age at T0		P-value difference between groups*
		10 years	12 years	15 years	10 vs. 12	10 vs. 15	12 vs. 15
T0	No. analyzed	91	91	86
	GMC TT-specific IgG µg/mL (95%CI)	5.1 (4.3–6.0)	1.6 (1.3–1.9)	0.7 (0.6–0.8)	<0.001	<0.001	<0.001
T1	No. analyzed	88	90	85
	GMC TT-specific IgG µg/mL (95%CI)	7.4 (6.5–8.5)	4.4 (3.4–5.1)	2.9 (2.4–3.5)	0.069	0.213	1.000
T2	No. analyzed	85	89	83
	GMC TT-specific IgG µg/mL (95%CI)	3.6 (3.1–4.2)	1.9 (1.6–2.2)	1.1 (1.0–1.4)	0.006	0.153	0.186
T1/T0	GMC ratio (95%CI)	1.49 (1.34–1.64)	2.75 (2.42–3.13)	4.26 (3.59–5.05)	<0.001	<0.001	<0.001
T1/T2	GMC ratio (95%CI)	2.03 (1.89–2.18)	2.34 (2.14–2.55)	2.50 (2.27–2.75)	0.048	0.001	0.921

NOTE: Differences between age groups in GMC of TT-specific IgG were determined with linear regression analyses, adjusting for concentrations at T0. GMC ratios indicate the level of increase (T1/T0) or decrease (T1/T2) between time points. Differences in GMC ratios between groups were determined with independent sample t-tests.

* P-values were adjusted for three comparisons with Bonferroni correction. Extensive results of the crude and adjusted linear regression analyses are outlined in supplementary table S1.