Shandong Provincial Key Laboratory of Infectious Disease Control and Prevention, Shandong and else where. BQ. 1.1 and XBB possess substitutions relative to BA. 5 and BA. 2, respectively, in the receptorbinding domain of their spike protein (appendix p 4), which is the major target for vaccines and therapeutic monoclonal antibodies (mAbs) for COVID-19. Both variants have the substitution R346T, which confers resistance to certain therapeutic antibodies, 1 raising concerns that mAbs or vaccines might be less effective against BQ. 1.1 and XBB than against other omicron strains. We showed that BQ. 1.1 and XBB have enhanced immune evasion capabilities compared with earlier omicron variants, including BA. 5 and BA. 2, by evaluating the efficacy of therapeutic mAbs against BQ. 1.1 and XBB. 2 However, the neutralising ability of plasma from convalescent individuals and COVID-19 vaccinees against BQ. 1.1 and XBB clinical isolates remained unknown. Accordingly, we evaluated the neutralising ability of antibodies in plasma from three different groups against BQ. 1.1 and XBB clinical isolates: individuals (180–189 days after the third dose; n= 20) who received three doses of the monovalent mRNA vaccine BNT162b2 (Pfizer–BioNTech) or mRNA-1273 (Moderna), or both; individuals (33–57 days after the fourth dose; n= 20) who received four doses of the monovalent mRNA vaccine BNT162b2 or mRNA-1273, or both; and indi viduals (29–89 days after the infection; n= 10) who received three doses of monovalent BNT162b2 or mRNA-1273 before the BA. 2 breakthrough infection. Using a live-virus neutralisation assay, we determined the 50% focus reduction neutralisation titre (FRNT50) of the plasma samples against BA. 2 (hCoV-19/Japan/UT-NCD1288-2N/2022), BA. 5 (hCoV-19/Japan/TY41-702/2022), BQ. 1.1 (hCoV-19/Japan/TY41-796/2022), and XBB (hCoV-19/Japan/TY41-795/2022). For plasma from individuals who received a third dose of the mRNA vaccine, 17 (85%) of 20 samples or 18 (90%)