Fig. 3: Introductions and regional dynamics of Delta transmission lineages.

a, The number of independent introductions per UTLA in England derived from continuous phylogeographic analysis of all Delta transmission lineages with more than five sequences. b, Trends in aggregate intra- and inter-UTLA mobility normalized to pre-pandemic levels (yellow) and the number of virus lineage movements between postcode districts. Letters denote stages of lockdown easing: A, schools re-open and limited outdoor mixing between households is permitted (8 March 2021); B, ‘stay at home’ directive is lifted, more outdoor mixing (up to six people from two households) is allowed (29 March 2021); C, non-essential retail, holiday lets and campsites re-open and outdoor dining is permitted (12 April 2021); D, indoor hospitality re-opens and indoor mixing is permitted (17 May 2021). c, The proportion of virus lineage movements between postcodes more than 25 km apart: the y axis denotes the proportion of movements that are less than or equal to the value on the x axis. This is shown for movements before lockdown easing (C (blue)), between C and D (yellow) and D (red). C and D are defined in b. d, Virus lineage movements inferred by continuous phylogeographic analysis for four example large transmission lineages (transmission lineages IV, VI and VII are shown in Extended Data Fig. 5). The direction of lineage movement is anticlockwise, and dots represent the start and end points of movements, coloured by inferred date. The size of each lineage and its inferred TMRCA date are shown below each map. Distance kernels for each lineage are shown in Extended Data Fig. 7.