Predicted domination of variant Delta of SARS-CoV-2 before Tokyo Olympic games, Japan

Using numbers of SARS-CoV-2 variants detected in Japan, the relative instantaneous reproduction numbers of the R.1, Alpha, and Delta variants with respect to other strains circulating in Japan were estimated at 1.245, 1.437, and 1.948, respectively. The numbers can vary within 1.190–1.319 for R.1, 1.335–1.580 for Alpha, and 1.703–2.30 for Delta depending on the assumed serial interval distributions. The frequency of the Delta is expected to take over the Alpha in Japan around July 12, 2021.