PA-specific IgG titers elicited by S. Typhi Ty21a-PA prime followed by AVA boost. Mice were primed i.n. with Ty21(pSECPA) (A), Ty21a(pVDL9.3PA83ec) (B) or Ty21a empty vector on days 0, 28 and 56 and boosted i.n. on day 112 with Ty21a(pSECPA) (A), Ty21a(pVDL9.3PA83ec) (B) or s.c. with 0.2 ml of AVA (A and B). To compare multiple vs. single priming, a group was immunized on day 0 with Ty21a(pSECPA) or Ty21a empty vector, and boosted on day 112 with 0.2 ml of AVA in identical manner (C). A positive control group received 2 doses of AVA on day 0 and 112 (D). Mice that received only PBS included as negative controls showed no responses (data not shown). Data represent GMT and the 95% confidence intervals for each group. Arrows indicate each immunization. * indicate differences between groups primed with Ty21a-PA strains vs. Ty21a empty vector (p<0.001); # indicate differences between Ty21a-PA prime AVA-boost vs. Ty21a-PA prime and boost.