TABLE 2.

Antibody generation after booster immunizations performed at different times after primary immunization with 1 μg of PA^a

Day of revaccination	Anti-PA Ab titer by ELISA		Neutralizing Ab titer
	GMT ± SD	No. of responders/total	GMT ± SD	No. of responders/total
0	<50 ± 1	0/12	<50 ± 1	0/12
14	381 ± 6.48	8/10	331 ± 4.26	7/10
28	7,000 ± 4.12	9/10	8,500 ± 3.59	9/10
65	12,000 ± 2.83	10/11	8,000 ± 4.24	9/11
180	10,000 ± 3.24	9/10	12,000 ± 2.35	9/10

^aThe PA vaccine (1 μg) was injected (0.5 ml s.c.) into 54 guinea pigs. Groups of 10 to 12 animals were boosted with the same PA vaccine dose on day 14, 28, 65, or 180 after the primary immunization. Anti- PA (ELISA) and neutralizing Ab titers were determined 14 days later as described in Materials and Methods. The day zero group was not boosted.