Since the COVID-19 outbreak first began in late December 2019, the evolution of the causative agent SARS-CoV-2 has led to the emergence of four variants of concern including the alpha (B.1.1.7) lineage that first emerged in the UK and the beta (B.1.351), gamma (P.1) and delta (B.1.617.2) lineages that were identified in South Africa, Brazil and India, respectively. Five variants of interest have also emerged, including the Eta (B.1.525), Iota (B.1.526), Kappa (B.1.617.1), Lambda (C.37), and Mu (B.1.621) lineages discovered in Nigeria, New York, India, Peru, and Columbia, respectively. The most recently recognized of these variants is the Mu (B.1.621) lineage, which was classified as a new variant of interest by the WHO on August 30th. By this point, the lineage had been detected in 39 countries. In Colombia, where the variant was first isolated in January, a huge surge in COVID-19 occurred between March and August, with cases reaching a peak of 33,594 per day on June 26th.Although the P.1 (gamma) variant of concern was dominant during the initial phase of this surge, B.1.621 outcompeted P.1 and all other variants in May and has driven the epidemic in Colombia since then.
Researchers in Japan have warned that the Mu (B.1.621) variant appears to be highly resistant to neutralization by sera from convalescent or vaccinated individuals. The B.1.621 variant, first isolated in Colombia in January this year (2021), was classified as a variant of interest by the WHO on August 30th. The resistance that emergent variants have so far exhibited can be attributed to several mutations that have arisen in the viral spike protein – the primary structure involved in mediating the infection of host cells. The majority of B.1.621 variants harbor the following eight spike mutations: T95I, YY144-145TSN, R346K, E484K, N501Y, D614G, P681H, and D950N. Several of these mutations are commonly seen in variants of concern, including E484K (present in B.1.351 and P.1), N501Y and P681H (present in B.1.1.7), and D950N (present in B.1.617.2). Now, Dr. Kei Sato and colleagues have conducted a study showing that the variant was more resistant to neutralization by serum-mediated neutralization than all other variants of interest or concern that have been identified to date.