A fourth dose of an mRNA COVID-19 vaccine increases antibody response in kidney transplant recipients (KTRs) who have a weak response after 3 doses, investigators reported in the Annals of Internal Medicine.

In a case series, 92 KTRs from 3 French university hospitals had antispike immunoglobulin G (IgG) titers less than 143 binding antibody units (BAU) per mL at 1 month after a third dose. They received a fourth dose at a median 68 days after the third dose, in keeping with a June 2021 approval from French health authorities for an extra dose in this population.

After a median 29 days, median IgG levels increased significantly from 16.4 to 145 BAU/mL and 50% of patients reached the threshold of 143 BAU/mL, Sophie Caillard, MD, PhD, of Hôpitaux Universitaires de Strasbourg in Strasbourg, France, and colleagues reported. Slightly more patients reached this threshold after the mRNA-1273 than BNT162b2 vaccine (52% vs 48%), with median response of 150 vs 122 BAU/mL.

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Antispike IgG titers exceeding 143 BAU/mL appear to be protective against the wild-type COVID-19 virus and the alpha, beta, and gamma variants, but neutralization of the delta variant requires higher antispike IgG titers, the investigators noted.

There were no new safety signals. One patient with IgG levels of 28 BAU/mL after the fourth vaccine dose later contracted mild COVID-19.

“Our study indicates that a fourth dose of an mRNA-based vaccine produces a satisfactory antibody response in some kidney transplant recipients who did not respond adequately after 3 previous doses, and it supports the use of a fourth vaccine dose for these patients,” Dr Caillard’s team concluded.


Caillard S, Thaunat O, Benotmane I, Masset M, Blancho G. Antibody response to a fourth messenger RNA COVID-19 vaccine dose in kidney transplant recipients: a case series. Ann Intern Med. Published online January 11, 2022.doi:10.7326/L21-0598