Diminished antibody response against SARS-CoV-2 Omicron variant after third dose of mRNA vaccine in kidney transplant recipients

Background: Available SARS-CoV-2 vaccines have reduced efficacy against the Omicron variant in immunocompetent individuals. Kidney transplant recipients (KTRs) have diminished antiviral responses to wild-type SARS-CoV-2 after vaccination, and data on antiviral responses to SARS-CoV-2 variants, including the Omicron variant, are limited. Methods: We conducted a prospective, multi-center cohort study of 51 adult KTRs who received three doses of BNT162b2 or mRNA-1273. Blood and urine samples were collected before and four weeks after the third vaccine dose. The primary outcome was anti-viral antibody responses against wild-type and variants of SARS-CoV-2. Secondary objectives included occurrence of breakthrough SARS-CoV-2 infection and non-invasive monitoring for rejection using serum creatinine, proteinuria, donor-derived cell-free DNA and donor-specific antibodies. Sera from pre-pandemic healthy controls and KTRs were used for comparison. Results: 67% of KTRs developed anti-wild-type spike antibodies after the third vaccine dose, similar to the Alpha (51%) and Beta (53%) variants, but higher than the Gamma (39%) and Delta (25%) variants. No KTRs had neutralizing responses to the Omicron variant before the third vaccine dose. After the third dose, fewer KTRs had neutralizing responses to the Omicron variant (12%) compared to wild-type (61%) and Delta (59%) variants. Three patients (6%) developed breakthrough SARS-CoV-2 infection at a median of 89 days. No KTRs developed allograft injury, de novo donor-specific antibodies or allograft rejection. Conclusion: In KTRs, a third dose of mRNA vaccines increases antibody responses against wild-type and variants of SARS-CoV-2, while neutralizing responses to the Omicron variant remain markedly reduced.