Dynamics of Covid-19 Delta Variant in the UK - the estimate of Reproduction Number.

Delta variant is considered as Variant of Concern (VOC) due to its high transmissibility compared to the original strain and other variants. This paper assessed the transmissibility of the delta variant in the UK from March to July by estimating effective reproduction numbers. First, effective reproduction number R at initial exponential phase of outbreak was calculated by using exponential growth method, then real time reproduction number Rt was estimated by using the time-dependent method. Depending on the observed generation interval distribution, R is 1.39 and Rt is merging to 1 along the time. The result is significantly lower than the basic reproduction number R0 reported by several institutions. From the first emergence of delta variant in UK to July, even though the daily infection cases were increasing due to step-by-step lockdown relaxation, the transmissibility of delta is slightly diminishing. Control measures especially the vaccination program are considered effective from this perspective. The analysis was performed based on daily cumulative delta infection number from March to July provided by Public Health England (PHE). R studio and Microsoft Excel were used in data processing and visualization.