European Centre for Disease Prevention and Control.Threat Assessment Brief:Rapid increase of a SARS-CoV-2 variant with multiple spike protein mutations observed in the United Kingdom.December 20,2020. https://www.ecdc.europa.eu/sites/default/files/documents/SARS-CoV-2-variant-multiple-spikeprotein-mutations-United-Kingdom.pdf.(2021.8.11アクセス)