Safety and Immunogenicity of the mRNA-1273 Coronavirus Disease 2019 Vaccine in Solid Organ Transplant Recipients

Background Solid organ transplant recipients (SOTRs) are at high risk for severe COVID-19.Methods This open-label, phase 3b trial evaluated mRNA-1273 in 137 kidney and 77 liver SOTRs and 20 immunocompetent participants. In part A, SOTRs received three 100-mu g doses of mRNA-1273; immunocompetent participants received 2 doses. In part B, an additional 100-mu g dose was offered >= 4 months after the primary series. Here, we report interim trial results.Results mRNA-1273 was well-tolerated in SOTRs. Four serious adverse events were considered vaccine related by the investigator in 3 SOTRs with preexisting comorbidities. No vaccine-related biopsy-proven organ rejection events or deaths were reported. mRNA-1273 elicited modest neutralizing antibody responses after dose 2 and improved responses after dose 3 in SOTRs. Post-dose 3 responses among liver SOTRs were comparable to post-dose 2 responses in immunocompetent participants. Post-additional dose responses were increased in SOTRs, regardless of primary series vaccination. In liver SOTRs, post-additional dose responses were similar to 3-fold higher versus post-dose 2 but lower than immunocompetent participant responses. Most kidney SOTRs received multiple immunosuppressants and had reduced antibody responses versus liver SOTRs.Conclusions mRNA-1273 was well-tolerated, and dose 3 and the additional dose improved antibody responses among SOTRs.Clinical Trials Registration NCT04860297. Messenger RNA-1273 (100 mu g) administered as a 3-dose primary series and an additional dose was well tolerated among solid organ transplant recipients. Antibody responses were improved after dose 3 and the additional dose, supporting the recommended doses for this immunocompromised population. Graphical Abstract