Fig 2. Estimates of the date of emergence of the Alpha variant in the United Kingdom (UK).
(A) The epidemic curve corresponding to the data used to calibrate the model, for context. A total of N = 406 samples carrying the Alpha variant were collected between September 20 and November 11, 2020 [21]. (B) Violin plots for the distributions of the date of emergence. We estimated the emergence of the Alpha variant in the UK at August 21 (95%IPR: Jul 23–Sep 5), 2020 (top, blue; upper and lower bound of the 95%IPR depicted by bars). For comparison, we also show the distributions of the estimates from an updated version of the model developed in [11]—which relies on a single observation on September 20—where we set R = 1.9 and a negative-binomial distribution for the number of the secondary cases (middle, orange). The distribution for the estimated time of most recent ancestor (tMRCA) [12] is also shown (bottom, gray).