Vaccine immunogenicity
Vaccine immunogenicity was evaluated for a subgroup of patients and controls by measuring serum IgG antibody levels against SARS-CoV-2 trimeric spike S1/S2 glycoproteins, 2–8 weeks after the second and the third vaccine doses. We used the FDA-authorized LIAISON (DiaSorin, Sallugia, Italy) quantitative assay. The assay provides an indication for the presence of neutralizing IgG antibodies against SARS-CoV-2 and its clinical sensitivity and specificity is >98%. A value of >15 binding antibody units (BAU) was considered positive according to the manufacturer’s instructions.