TABLE 2.

Functional antibody activity and IgG antibody concentrations in infant sera following administration of full or fractional-dose regimens of the Hib PRP-T conjugate vaccine

Regimen	SBA GMTa	Avidity index (mean ± SE)b	ELISA IgG GMC (μg/ml)
Full dose (n = 19)c	85.0	71.9 ± 9.4	13.0
One-half dose (n = 19)	82.0	123.6 ± 26.8	13.7
One-third dose (n = 22)	76.2	150.9 ± 24.9d	17.0

^aTiters were defined as the reciprocal of the dilution with ≥50% killing of the initial inoculum. 

^bAvidity index of the IgG anti-PRP antibodies in the presence of 0 to 4 M NaSCN. The avidity index was calculated as the weighted average of the NaSCN molar concentration times the dilution factor. 

^cThe SBA GMTs for the full-dose and one-half dose regimens were calculated with 18 instead of 19 serum samples. One serum sample in each of these groups exhibited >25% killing in the growth controls; SBA titers could not be determined. 

^dA significant difference (P = 0.024) compared to the full-dose regimen. The Mann-Whitney rank sum test was used for comparison of groups of data. No other significant differences were found.