TABLE 4.

Serum bactericidal antibody responses of selected adults and children to meningococcal vaccination^a

Subject or pool no. (mean age [yr])	Strain 4243 (OAc positive)			Strain 4335 (OAc negative)
	Reciprocal titer in preimmunization sera	Postimmunization sera		Reciprocal titer of preimmunization serab	Postimmunization sera
		1/Titerb	BC50c		1/Titer	BC50c
Subjects
54 (adult)	<4	<4	INDETd	<4	<4	INDET
55 (adult)	<4	21	2.3	<4	101	0.4
60 (adult)	<4	50	1.1	<4	170	0.1
Pools
1 (9.5)	<4	100	1.1	<4	300	0.3
2 (4.5)	<4	<4	>3.5	<4	12	0.6
3 (4.6)	NDe	<4	>3.0	ND	<4	>2.2
4 (2.6)	<4	<4	INDET	<4	<4	INDET

^aFor description of pools, see footnote a of Table 3.

^bDilution of sera giving 50% killing in the presence of human complement. Note that all sera with titers of <1:4 were also negative (titer, <1:4) when retested with rat complement.

^cBC₅₀ for strain 4243 was calculated from the total antibody concentration measured by the RABA divided by the reciprocal bactericidal titer. A similar calculation was done to calculate the BC₅₀ of strain 4335 except that the total anticapsular antibody concentration was adjusted to take into consideration the percentage inhibition by soluble OAc-negative polysaccharide (i.e., the portion specific for OAc-negative polysaccharide equals the total antibody concentration measured by RABA multiplied by the percent inhibited by OAc-negative polysaccharide in the ELISA (see Fig. 1).

^dINDET, indeterminate because of low concentrations of anticapsular antibody.

^eND, not done.