In Germany, where Delta is still rare, scientists expect it to make up the majority of Covid-19 infections in the coming months.
In the U.K., Delta is already dominant and scientists estimate it is between 40% and 80% more transmissible than the Alpha variant, which first took hold in England and is itself about 50% more transmissible than the original virus that emerged in Wuhan, China, in late 2019, according to British public-health experts.
Still, the rebound in infections has prompted the British government to push back lifting public-health restrictions—such as limits on the size of gatherings and mask requirements—by a month, to mid-July.