<i>Y. pestis</i> Kim53ΔJ+P strain confers prolonged protection against plague.

<p>(A) Mice (7–8 per group) were infected subcutaneously with 1×10⁵ cfu of Kim53ΔJ+P (circle); EV76 (× symbol); or EV76ΔJ+P (triangle). Control animals were treated with saline (square). Animals were bled for ELISA determination of anti-F1 antibody titers 45 days following immunization. Titers following immunization with Kim53ΔJ+P ranged from 64,000 to 100,000, with GMT of 18,500, while titers for the EV76 or EV76ΔJ+P immunized animals ranged from 640 to less than 10, with GMT of 30 and 10, respectively. Animals were challenged subcutaneously with 1×10³ cfu (∼1×10³ LD₅₀) of <i>Y. pestis</i> Kim53 (panel A) or intranasally with 8×10³ cfu (∼15 LD₅₀) of <i>Y. pestis</i> Kim53 (panel B).