Randomization and blinding
Participants were enrolled by randomization into two treatment groups according to the following steps. A master log of all screened participants was maintained. At screening, participants who signed the informed consent form and met all inclusion and none of the exclusion criteria were identified as eligible to be enrolled in the study. Eligible participants were assigned a sequential identification number when they presented to the clinic on Study Day 0. Statisticians at DF/Net Research (Seattle, WA) generated the list of randomized treatment assignments and included it in the enrollment module of the Interactive Web Randomization System (IWRS), which is integrated into the DFexplore software. The study coordinator or designee at the clinical site performed the enrollment and randomization using DFexplore. Block randomization of appropriate size was used to balance enrollment in a 1:1 ratio into each of the two groups. A designated individual at the study site was provided with a treatment key, which linked the treatment code to the actual treatment assignment and was kept in a secure place.The study was conducted as a double-blind trial. Participants, investigators, study personnel performing any study-related assessments following study injection, and laboratory personnel performing immunology assays were blinded to treatment assignment. The randomization scheme from DF/Net Research was provided to unblinded study personnel (i.e., site pharmacists performing study product preparations and unblinded study product administrators).