Several new variants of SARS-CoV-2 have emerged since fall 2020 which have multiple mutations in the receptor binding domain (RBD) of the spike protein. Objective: We aimed to assess how mutations in RBD affected recognition of immune sera by antibodies induced by natural infection versus immunization with BNT162b2, a mRNA- based vaccine against COVID-19. Methods: We produced SARS-CoV-2 RBD mutants with single mutations in the receptor binding domain (RBD) region (E484K, K417N, N501Y) or with

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... l 3 mutations combined, as occurring in the newly emerged variants B.1.351 (South Africa) and P.1 (Brazil). Using standard and avidity ELISAs, we determined the binding capacities to mutant RBDs of antibodies induced by infection versus vaccination. Results: These binding assays showed that vaccination induced antibodies recognize both wildtype and mutant RBDs with higher avidities than those raised by infection. Nevertheless, recognition of mutants RBDK417N and RBDN501Y was 2.5-3-fold reduced while RBDE484K and the triple mutant were 10-fold less well recognized, demonstrating that the mutation at position 484 was key for the observed loss in cross-reactivity. Conclusion: Our binding data demonstrate improved recognition of mutant viruses by BNT162b2-induced antibodies compared to those induced by natural infection. Recognition may, however, be 10-fold reduced for the variants B.1.351/P.1, suggesting that the development of a new vaccine is warranted. The E484K mutation is an key hurdle for immune recognition, convalescent plasma and monoclonal antibody therapy as well as serological assays based on the wildtype sequence may therefore seriously impaired.