LONDON—British Key Minister Boris Johnson, preventing a severe coronavirus infection, was admitted to the intensive-treatment unit of a London clinic Monday night, leaving his country’s management in query at a minute of deep crisis as the virus’s distribute accelerates.

As Mr. Johnson’s situation worsened, he deputized his foreign secretary, Dominic Raab, to operate the governing administration, a spokesman mentioned. The fifty five-12 months-aged leading was conscious when he was wheeled into the intensive-treatment unit of a central London clinic at all-around seven p.m….