Safety and Immunogenicity of the mRNA-1273 COVID-19 Vaccine in Solid Organ Transplant Recipients.

BACKGROUND: Immunosuppressed individuals, including 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 adult kidney and 77 liver SOTRs and 20 immunocompetent participants. In Part A, SOTRs received three 100-µg doses of mRNA-1273; immunocompetent participants received 2 doses. In Part B, an additional 100-µg dose was offered ≥4 months post-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 pre-existing comorbidities. No vaccine-related biopsy-proven organ rejection events or deaths were reported. mRNA-1273 elicited modest neutralizing antibody (nAb) 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 the primary series vaccination. In liver SOTRs, post-additional dose responses were ∼3-fold higher versus post-dose 2 but were lower than immunocompetent participant responses. Most kidney SOTRs received multiple immunosuppressants and had reduced antibody responses versus liver SOTRs. CONCLUSIONS: mRNA-1273 (100 µg) was well-tolerated and dose 3 and the additional dose improved antibody responses among SOTRs.