Emerging SARS-CoV-2 B.1.621/Mu variant is prominently resistant to inactivated vaccine-elicited antibodies

Although it first appeared almost two years ago,the COVID-19 pandemic continues to have an impact on a global scale,in part due to newly emerging SARS-CoV-2 variants such as Delta and Lambda.The B.1.621 variant,first identified in Colombia in January 2021,was classified as a variant of interest(VOI)and designated as Mu by the World Health Organization(WHO)in August 2021.However,its infectivity and resistance to neutralizing antibodies remain largely unknown.Here,in comparison to Delta,the Mu variant showed an unexpectedly enhanced immune resistance to inactivated vaccine-elicited antibodies.Nevertheless,Mu demonstrated less infectivity than Delta,implying a biological trade-off between viral transmission and immune escape.This study strongly calls for urgent evaluation of the protective efficacy of current COVID-19 vaccines against the Mu variant.Variants of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)are of concern regarding control of the global COVID-19 pandemic(Wang et al.,2021).The SARS-CoV-2 B.1.621 variant was first identified in Colombia in January 2021.Considering its epidemiological prevalence,the WHO defined B.1.621(named Mu)as a VOI on 30 August 2021.As of September 2021,the WHO has classified four variants of concern(VOC),i.e.,Alpha(B.1.1.7),Beta(B.1.351),Gamma(P.1),and Delta(B.1.617.2),and two VOI,i.e.,Lambda(C.37)and Mu(B.1.621)(Supplementary Figure S1A).