Abstract
Coronavirus disease 2019（COVID-19）is a newly emerging human infectious disease caused by severe acute respiratory syndrome coronavirus 2（SARS-CoV-2）．It had been first identified in Wuhan at the end of 2019 and the spread of SARS-CoV-2 variants has become a crucial issue worldwide. WHO categorized SARS-CoV-2 variants as "Variants of Concern; VOCs" and "Variants of Interest; VOIs" based on transmissibility, disease severity or their susceptibility to vaccines. Especially, the spread of SARS-CoV-2 variant categorized in VOCs, such as B.1.1.7 and B.1.617.2, has been a serious concern worldwide. In Japan, in addition to the B.1.1.214/B.1.1.284 variants, the B.1.1.7 variant has been rapidly spreading in Osaka and Tokyo. The B.1.617 variant was first identified in April 2021 in a patient who was under domestic quarantine and cases of community-acquired infections of the B.1.617.2 variant were first observed in May 2021. Amino acid changes in the spike protein, such as the N501Y, E484K or L452R mutations mainly observed in VOCs in addition to the D614G mutation are thought to affect the transmissibility and immune escape of the virus as well as the disease severity and this may be contributory to the rapid spread of SARS-CoV-2 variants. Now, several SARS-CoV-2 variants with additional mutations are continuously emerging worldwide and the prevailing SARS-CoV-2 variants are rapidly changing.
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