Functional humoral and cellular response of monovalent COVID-19-vaccines against Omicron BA.2 variant of SARS-CoV-2 in patients with chronic lymphocytic leukemia

We designed a prospective study to evaluate the humoral (using a surrogate virus neutralization test) and cellular (using an IFN-c ELISpot) immune response among patients with chronic lymphocytic leukemia (CLL) against Wuhan-Hu-1 and Omicron BA.2 strains of SARS-CoV-2, after mRNA-based vaccination. The proportion of patients with a functional humoral response was higher among untreated CLL patients compared to treated CLL patients against both Wuhan- Hu-1 and Omicron BA.2 after the second and the third dose of vaccination, and at 12 months after the first dose. The proportion of positive cellular response against the peptide pool cover- ing the full-length Wuhan-Hu-1 spike protein was similar between untreated and treated CLL patients at all three timepoints. The cellular response to the mutated regions of BA.2 spike pro- tein was lower than the response to the corresponding regions in the ancestral spike after the second dose, but this difference was eliminated after the third dose.