British Prime Minister Boris Johnson plans to reopen England's economy from coronavirus lockdown on July 19, but if he does so, it won't be without disquiet from some of the scientists whose advice he has followed thus far.

Despite one of the world's highest vaccination rates, Britain is facing a new wave of Covid-19. Johnson is taking a gamble: rather than shutting the country down, he is aiming to live with the virus in what is a world-first test case of the ability of vaccines to protect from the Delta variant.

Johnson has already delayed the so-called "freedom day" by four weeks to allow more people to get vaccinated, after warning that thousands more people might die...