Predicted dominance of variant Delta of SARS-CoV-2 before Tokyo Olympic Games, Japan, July 2021

Using numbers of SARS-CoV-2 variants detected in Japan as at 13 June 2021, relative instantaneous reproduction numbers (R-RI) of the R.1, Alpha, and Delta variants with respect to other strains circulating in Japan were estimated at 1.25, 1.44, and 1.95. Depending on the assumed serial interval distributions, R-RI varies from L20-1.32 for R.1, 1.34-1.58 for Alpha, and 1.70-2.30 for Delta. The frequency of Delta is expected to take over Alpha in Japan before 23 July 2021.

Automated summary

Based on the numbers of SARS-CoV-2 variants detected in Japan as of June 13, 2021, the relative instantaneous reproduction numbers (R-RI) of the R.1, Alpha, and Delta variants were estimated. The R-RI values indicate that the Delta variant is expected to surpass the Alpha variant in frequency in Japan before July 23, 2021.