<qa>  What is the Phase 1 double-blind, randomized, placebo-controlled study?This is a Phase 1, double-blind, randomized, placebo-controlled study to evaluate the safety, tolerability, and immunogenicity of Px563L or RPA563 administered intramuscularly. All subjects will be followed for safety and tolerability for 393 days after the initial vaccination. Immunogenicity analyses will be performed for up to 182 days, including an interim analysis based on Day 70 results, after the initial vaccination. 