TABLE 1.

Kinetics of the cellular immune response to serovar Typhi Ty21a^a

No. of days after vaccination	Frequency of respondersb
	T-cell proliferation	IFN-γ production
3	0/2	0/2
7	6/8	6/8
14	4/8	6/8
21	3/8	4/8
36	1/2	2/2

^aPeripheral blood T cells were stimulated with 10⁷ heat-killed serovar Typhi Ty21a bacteria/ml.

^bA significant response is defined as a >2-fold increase in the rate of proliferation or IFN-γ production compared to the level before vaccination in either the CD4⁺- or the CD8⁺-T-cell population. Values are numbers of vaccinees who responded/total numbers of vaccinees.