Moderna, Inc. announced positive seven-month interim safety and immunogenicity data after the third and final vaccination in the Phase 1 study of its investigational cytomegalovirus (CMV) vaccine (mRNA-1647). The findings build on the previously reported three-month interim analysis, after two vaccinations, announced at the company’s R&D Day in September 2019. Additionally, the Company announced that the first participant was dosed in the Phase 2 dose-confirmation study. mRNA-1647 is a wholly owned program in Moderna’s prophylactic vaccines portfolio. mRNA-1647 comprises six mRNAs encoding two antigens in one vaccine, and is designed to protect against CMV infection. Of the six mRNAs, five encode the subunits of the CMV pentamer complex and one mRNA encodes the glycoprotein B (gB) protein, both of which are highly immunogenic. Both pentamer and gB proteinsare essential for CMV to enter epithelial cells, which is the first step in CMV infection. mRNA-1647 is designed to produce an immune response to both pentamer and gB antigens to prevent CMV infection. The second interim analysis of the Phase 1 trial reports safety and immunogenicity of the first three dose levels (30, 90 and 180 µg) through seven months (one month after the third vaccination) and the highest dose level (300 µg) through three months (one month after the second vaccination). Neutralizing antibody titers were assessed in two assays utilizing epithelial cells and fibroblasts, which measure immune response to pentamer and gB antigens, respectively. Safety data were consistent with those reported at the three-month interim analysis. The vaccine was generally well-tolerated and there were no vaccine-related serious adverse events (SAEs). The most common solicited local adverse reaction (AR) across all vaccinations was injection site pain (54-100% of a given treatment group). The most common solicited systemic ARs reported overall were headache, fatigue, myalgia and chills. Fever was reported in 0-55% of CMV-seronegative treatment groups and in 8-67% of CMV-seropositive treatment groups. The most common Grade 3 solicited ARs were in CMV-seropositive participants, and were fatigue (0-27% of a given treatment group), chills (0-27% of a given treatment group) and fever (0-33% of a given treatment group). In general, the highest solicited systemic AR rates were reported after the second vaccination, were more frequent in the CMV-seropositive compared to the CMV-seronegative group, and tended to correlate to dose. As reported in the previous interim analysis, one related Grade 4 adverse event (AE) has been observed, which was an isolated lab finding of elevated partial thromboplastin time (PTT), which was elevated at baseline (Grade 1) and self-resolved on the next lab test with no associated clinical findings.