Memory B cell repertoire from triple vaccinees against diverse SARS-CoV-2 variants

Omicron,the most heavily mutated SARS-CoV-2 variant so far,is highly resistant to neutralizing antibodies,raising unprecedented concerns about the effectiveness of antibody therapies and vaccines 1,2.We examined whether sera from individuals who received two or three doses of inactivated vaccine,could neutralize authentic Omicron.The seroconversion rates of neutralizing antibodies were 3.3%(2/60)and 95%(57/60)for 2-and 3-dose vaccinees,respectively.For three-dose recipients,the geometric mean neutralization antibody titre(GMT)of Omicron was 16.5-fold lower than that of the ancestral virus(254).We isolated 323 human monoclonal antibodies(mAbs)derived from memory B cells in 3-dose vaccinees.