Riley, S., Wang, H., Eales, O., Haw, D., Walters, C. E., Ainslie, K. E. C., … Barclay, W. (2021, June 21). REACT-1 round 12 report: resurgence of SARS-CoV-2 infections in England associated with increased frequency of the Delta variant. https://doi.org/10.1101/2021.06.17.21259103.