Immunogenicity and safety evaluation of a recombinant protective antigen anthrax vaccine (GC1109): A phase II,...

GC1109, a novel recombinant protective antigen (PA) anthrax vaccine, has demonstrated promising immunogenicity in previous dose-finding trials. This study evaluated the immunogenicity and safety of four intramuscular doses of GC1109 in healthy adults.

This randomized, double-blind, placebo-controlled phase 2 trial enrolled healthy volunteers aged 19 to 65 years. Participants were assigned in a 3: 1 ratio to receive either GC1109 (1.0 mL) or placebo at weeks 0, 4, 8, and 32. Immunogenicity was assessed using toxin neutralization antibody (TNA) titers and anti-PA IgG levels. The primary endpoint was the proportion of vaccine recipients achieving a TNA 50 % neutralization factor (NF₅₀) ≥ 0.56 at week 36. Safety was evaluated through solicited and unsolicited adverse events (AEs).

All participants in the GC1109 group achieved TNA NF₅₀ ≥ 0.56 at week 36 (100 %, 95 % confidence interval: 97.6-100.0) and the predefined criterion for the primary endpoint was met. TNA and anti-PA IgG levels peaked at week 36 but declined thereafter. Pruritus was the only solicited AE significantly more frequent in the GC1109 group; serious AEs were rare and unrelated to vaccination.

Four doses of GC1109 were immunogenic and generally well-tolerated. Further studies are needed to explore appropriate boosting strategies and evaluate safety in larger populations.