Comparison of the evolutionary phylodynamic of Delta and Omicron variants of SARS-CoV-2

Due to the inconsistency of the information regarding the evolution of the last two waves caused by the Delta and Omicron variants, we are attempting to provide a phylodynamic analysis. We used the nucleotide sequences of the Delta (n = 89) and Omicron (n = 74) variants recorded in the GISAID database to perform an analysis based on the contemporary model of the birth-death horizon. An average rate of evolution of 3.677 × 10^− 4 subs /site/year (range,1.311× 10^− 4−6.144×10^− 4 ) for the DELTA variant, this gives an estimated mean of tMRCA corresponding to the root of the tree dated at 43.5 days. While for OMICRON a mean evolutionary rate of 3.898×10 − 3 subs/site/year (range,2.686×10^− 3 − 5.102×10^− 3) gave an estimated mean of tMRCA corresponding to the root of the tree dated at 26.4 days. The median of Re for the Indian DELTA = 1.81 (range, 0.196–3.94), and increased to 3.837 ≈ 4 on March 30, 2021. While for the South African OMICRON Re = 0.97 (range,0.41–1.54), and rose to 9.59 ≈ 9 on December 14, 2021. The average doubling times of the two waves are estimated respectively at 9 days for the DELTA variant and at 3 days for the OMICRON variant. The spread of the OMICRON pandemic is almost three times faster than that of the DELTA. The mean doubling times of the two waves are 9 days for the DELTA variant and 3 days for the OMICRON variant, respectively. As a result, the OMICRON pandemic is spreading nearly three times faster than the DELTA.