For this study, researchers wanted to test a subunit plague vaccine’s one-year immunogenicity and safety. In the first research, 240 healthy people between the ages of 18 and 55 were given two doses of 15 or 30 g plague vaccine on days 0 and 28, respectively. They tested the immunogenicity and safety of the plague vaccination for up to a year in our prolonged follow-up research. Titers of antibodies to envelope antigen fraction 1 (F1) antigen reached new highs at month 6, then gradually dropped to month 12, but remained higher than at day 56. At months 6 and 12, geometric mean titers (GMTs) of F1 were considerably greater in the 30 µg group than in the 15 µg group (P<0.0001 and P<0.001). At both time intervals, however, approximate 100% seroconversion rates of F1 antibodies were detected in both the 15 and 30 µg groups. Titers and seroconversion rates for antibodies to recombinant virulence (RV) antigen dropped dramatically at month 6 and continued to fall at month 12. The GMTs and seroconversion rates in the 15 and 30 µg groups were not substantially different. There were no significant adverse events (SAEs) associated with the vaccination.

In individuals aged 18–55 years, the novel plague vaccine (F1+rV) generated a strong immune response that lasted up to 12 months and had an excellent safety profile.