A fourth dose of the mRNA-1273 SARS-CoV-2 vaccine improves serum neutralization against the delta variant in kidney transplant recipients

In immunocompetent subjects, the effectiveness of SARS-CoV-2 vaccines against the delta variant appears three- to five-fold lower than that observed against the alpha variant. Additionally, three doses of SARS-CoV-2 mRNA-based vaccines might be unable to elicit a sufficient immune response against any variant in immunocompromised kidney transplant recipients. This study describes the kinetics of the neutralizing antibody (NAbs) response against the delta strain before and after a fourth dose of a mRNA vaccine in 67 kidney transplant recipients who had experienced a weak antibody response after three doses. While only 16% of patients harbored NAbs against the delta strain prior to the fourth injection – this percentage raised to 66% afterwards. We also found that, after the fourth dose, the NAbs titer increased significantly (p=0.0001) from <7.5 (IQR : <7.5−15.1) to 47.1 (IQR <7.5−284.2). Collectively, our data indicate that a fourth dose of the mRNA-1273 vaccine in kidney transplant recipients with a weak antibody response after three previous doses improves serum neutralization against the delta variant.