Large-scale Synchronized Replacement of Alpha strain by the Delta Strain

In this letter, we report a large-scale synchronized replacement pattern of the Alpha strain by the Delta strain. We argue that this phenomenon is associated with the invasion timing and transmissibility advantage of the Delta strain. Alpha strain skipped some countries/regions, e.g. India and neighboring countries/regions, which led to a mild first wave before the invasion of the Delta strain, in term of reported COVID-deaths per capita.