Quantitative anti-F1 and anti-V IgG ELISAs as serological correlates of protection against plague in female Swiss Webster mice.

A recombinant fusion protein composed of Yersinia pestis fraction 1 capsule (F1) and virulence-associated V antigen (V) (F1-V) has been developed as the next-generation vaccine against plague. In this study, female Swiss Webster mice received a single intramuscular vaccination with one of eight doses of the F1-V vaccine and exposed 4 weeks later to either Y. pestis CO92 or C12 organisms by the subcutaneous or aerosol routes of infection. Quantitative anti-F1 and anti-V immunoglobulin G (IgG) ELISAs were used to examine the relationship between survival outcome and antibody titers to F1 and V. Results suggested that each 1log(10) increase in week 4 quantitative anti-F1 and anti-V IgG ELISA titers were associated with a 1.7-fold (p=0.0051) and 2.5-fold (p=0.0054) increase in odds of survival, respectively, against either bubonic or pneumonic plague and may serve as serological correlates of protection.