The simultaneous application of tetramerized RBDs of the Wuhan strain and the Omicron BA.1 strain in flow cytometry revealed that a considerable proportion of the triple-vaccinated individuals with breakthrough Omicron-infections were able to mount B-cell responses specific to the Omicron spike protein, which is in agreement with the increased neutralization titers against Omicron. This evidence concerns the gene CHMP5 and infection.