Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain
the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in
Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles
When the first cases of the SARS-CoV-2 Delta variant were detected in the United Kingdom in mid-April, the nation was getting ready to open up. COVID-19 case numbers, hospitalizations and deaths were plummeting, thanks to months of lockdown and one of the world’s fastest vaccination programmes. Two months later, the variant, which was first detected in India, has catalysed a third UK wave and forced the government to delay the full reopening of society it had originally slated for 21 June.