Table 2.

Numbers of positive specimens at various proposed cutoffs

Sampling time	na	No. (%) of specimens positive at proposed cutoff of:
		94 EU/ml	125 EU/ml	200 EU/ml
Baseline	102	0 (0)	0 (0)	0 (0)
1 wk	98	2 (2)	0 (0)	0 (0)
2 wk	96	6 (6.2)	2 (2.1)	1 (1)
4 wk	94	6 (6.4)	3 (3.2)	0 (0)
3 mo	57	2 (3.5)	1 (1.8)	0 (0)
6 mo	54	0 (0)	0 (0)	0 (0)
9 mo	47	0 (0)	0 (0)	0 (0)
12 mo	51	0 (0)	0 (0)	0 (0)
18 mo	43	0 (0)	0 (0)	0 (0)
24 mo	39	0 (0)	0 (0)	0 (0)

^aNumber of measurements available at each sampling time for the entire cohort. Note that for several subjects, specimens were not available for all sampling times between their prevaccination and last sampling times.