TABLE 2.

Protective efficacy 4 days post-challenge

Shigella serotype	LPS multiplier	Number of eyes protected/total	Protective efficacy a (%)	P-value b
S. flexneri 2a	1×	0/12	0%	1.0
	2×	5/12	42%	0.040
	4×	9/12	75%	0.0005
	8×	7/12	58%	0.005
	Saline	0/10	–	–
S. flexneri 3a	1×	8/12	60%	0.036
	2×	9/12	70%	0.012
	4×	7/12	50%	0.089
	8×	6/12	40%	0.193
	Saline	2/12	–	–
S. flexneri 6	1×	8/14	44%	0.120
	2×	8/14	44%	0.120
	4×	7/14	35%	0.237
	8×	10/14	63%	0.021
	Saline	3/13	–	–
S. sonnei	1×	11/12	92%	<0.0001
	2×	9/12	75%	0.0003
	4×	7/12	58%	0.005
	8×	9/12	75%	0.0003
	Saline	0/12	–	–

^a Calculated as [(% disease in control animals − % disease in vaccine group)/% disease in control animals] × 100.

^b P-values determined by Fisher’s exact test of experimental group compared to saline control group.