B cell antigen receptor (BCR) diversity increases by several orders of magnitude due to the action of terminal deoxynucleotidyl transferase (TdT) during V(D)J recombination. Unlike adults, infants have limited BCR diversity, in part due to reduced expression of TdT. Since human infants and young mice respond poorly to polysaccharide vaccines, such as the pneumococcal polysaccharide vaccine Pneumovax23 and Vi polysaccharide (ViPS) of Salmonella enterica serovar Typhi, we tested the contribution of TdTmediated BCR diversity in response to these vaccines. We found that TdT +/- and TdT -/- mice generated comparable antibody responses to Pneumovax23 and survived Streptococcus pneumoniae challenge. Moreover, passive immunization of B cell-deficient mice with serum from Pneumovax23-immunized TdT +/- or TdT -/- mice conferred protection. TdT +/- and TdT -/- mice generated comparable levels of anti-ViPS antibodies and antibody-dependent, complement-mediated bactericidal activity against S. Typhi in vitro. To test the protective immunity conferred by ViPS immunization in vivo, TdT +/- and TdT -/- mice were challenged with a chimeric Salmonella enterica serovar Typhimurium strain expressing ViPS, since mice are nonpermissive hosts for S. Typhi infection. Compared to their unimmunized counterparts, immunized TdT +/- and TdT -/- mice challenged with ViPS-expressing S. Typhimurium exhibited a significant reduction in the bacterial burden and liver pathology. These data suggest that the impaired antibody response to the Pneumovax23 and ViPS vaccines in the young is not due to limited TdTmediated BCR diversification.