To assess the effect of the updated mRNA JN.1 omicron vaccine (bretovameran, BioNTech/Pfizer, Mainz, Germany) in an immunocompromised and elderly population, we measured humoral immune responses after mRNA omicron JN.1 vaccination in 37 haemodialysis patients before and 21 days after vaccination. We observed a 3-fold change in anti-S IgG, and a 4.7-fold change in anti-S omicron IgG. Memory B cells (MBC) exclusively binding the receptor binding domain (RBD) of JN.1 displayed a median frequency of 0.11% before vaccination and changed significantly 3.9-fold to a median of 0.43%. Cross reactive JN.1 RBD and Wuhan-Hu-1 S-binding MBCs and MBCs only binding to Wuhan-Hu-1 S changed 2.3-fold and 1.8-fold, respectively. Using a vesicular stomatitis virus-based pseudovirus particle (pp) neutralisation assay, baseline response rates were 86% for XBB.1.5pp, 78% for JN.1pp, 73% for and KP.2pp, 65% for KP.2.3pp and KP.3pp, and 68% for LB.1pp. After vaccination, the response rates for all pseudoviruses increased significantly, and we observed a mean increase in neutralisation of XBB.1.5pp, JN.1pp, KP.2pp, KP.2.3pp, KP.3pp, and LB.1pp of 8.3-fold, 18.7-fold, 22.5-fold, 18.7-fold, 25.5-fold, and 23.5-fold, respectively. In summary, our report provides first evidence for a firm humoral immune response in dialysis patients after mRNA omicron JN.1 vaccination. Our data suggest that the vaccine could be highly effective at enhancing protection of vulnerable populations against evolving SARS-CoV-2 variants.

SP conducted contract research (testing of vaccinee sera for neutralising activity against SARS-CoV-2) for Valneva unrelated to this work. SP served as advisor for BioNTech, unrelated to this work, GMNB served as lecturer for Pfizer unrelated to this work. AD-J and TW served as advisors for Pfizer unrelated to this work. The other authors declare no competing interests.

A.D.-J. and G.M.N.B. received funding (Niedersaechsisches Ministerium fuer Wissenschaft und Kultur; 14-76103-184, COFONI Network, project 4LZF23), G.M.N.B. acknowledges funding by the European Regional Development Fund ZW7-85151373, and A.D.-J. acknowledges funding by European Social Fund (ZAM5-87006761). S.P. received funding by the EU project UNDINE (grant agreement number 101057100), the COVID-19-Research Network Lower Saxony (COFONI) through funding from the Ministry of Science and Culture of Lower Saxony in Germany (14-76103-184, projects 7FF22, 6FF22, 10FF22) and the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG; PO 716/11-1).

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