LONDON—The scientist behind a bombshell coronavirus study that reportedly shocked Washington and London out of their light-touch response to the pandemic has gone into self-isolation after experiencing symptoms of COVID-19.

Prof. Neil Ferguson, whose terrifying Imperial College report has been cited by the White House and Downing Street, said this morning that he had come down with the classic symptoms of a persistent dry cough and fever.

He was present at a press conference with Prime Minister Boris Johnson at No. 10 just 24 hours before his symptoms first appeared.

Ferguson was the lead scientist on a report published Monday that said 2.2 million Americans and more than half a million Brits would be killed by the COVID-19 disease unless drastic steps were taken to halt the spread of the virus.

In the days since the report was published, tens of thousands of bars, restaurants, schools, and theaters have been shuttered across the U.S. and Britain, while the authors of the report have become cult social-media heroes.

While word of his analysis was racing around the world, Ferguson began to retreat from public life. He said he felt the first signs of a cough on Tuesday morning during an interview with the Today Show on BBC Radio 4, just hours after Johnson had radically altered the British government’s coronavirus response after reading his report.

“I got a slight cough, actually while I was being interviewed by you yesterday,” he said after calling in to the show again on Wednesday morning.

“In the abundance of caution, I self-isolated then, so I’m stuck in my flat on my own for seven days in central London. Then at 4 o’clock in the morning I got a high fever, which is somewhat better now but I still feel fairly grotty.”

Ferguson is one of the top coronavirus advisers to the British government, which means he has been in countless meetings with the officials battling the pandemic over the past two weeks, including the prime minister himself.

“I’ve been in so many meetings in the last few weeks, and a number of my colleagues from other universities who have been advising the government in those meetings have also developed symptoms,” he told the BBC.

Before the report was published on March 16, Britain’s only official response to the virus was urging people to wash their hands.

No. 10 insists there was no policy U-turn, explaining that it had always said there would be a gradual ratcheting up of counter-viral measures. The stark change of approach suggests otherwise, and the Imperial College report suggested there had been a miscalculation of the required capacity of intensive-care beds.

Johnson has now urged Britons to avoid all non-essential contact with others and told people not to go to cinemas, restaurants, pubs, or other social events. There has been no official shutdown. Many venues in Britain have since chosen to close down, but pubs in North London were still groaning with revelers in novelty hats on Tuesday night, St. Patrick’s Day. Schools in Britain remain open.

The White House also cited the report published by the Imperial College COVID-19 Response Team.

Deborah Birx, who is coordinating the White House coronavirus task force, reportedly said the administration was particularly focused on the report’s conclusion that the entire household should stay in isolation for 14 days if any member of it suffered from COVID-19 symptoms.