U.K. Prime Minister Boris Johnson, who is battling coronavirus, remains in intensive care after a third night in hospital, though he is in stable condition.

Johnson was admitted to the ICU at St. Thomas’s Hospital in London on Monday night at 7 p.m. local time, having first entered the hospital for precautionary testing on Sunday night. The ICU move was to allow Johnson to be closer to a ventilator if necessary.

A Downing Street spokesperson has said the PM is in “good spirits,” though he is being monitored closely.

The spokesperson said Tuesday that Johnson had been “receiving standard oxygen treatment and is breathing without any other assistance. He has not required mechanical ventilation or non-invasive respiratory support.”

The 55-year-old Johnson is the first major world leader to have revealed a coronavirus diagnosis.

Buckingham Palace said Tuesday that Queen Elizabeth sent a message to Johnson — with whom she traditionally speaks with each week in a private briefing — and his pregnant partner Carrie Symonds, saying they were in her thoughts and wishing Johnson a speedy recovery.

Meanwhile, Prince William also tweeted his wishes to Johnson on Tuesday: “Our thoughts are with the Prime Minister and his family, who like so many in the U.K. and around the world are affected by coronavirus. We wish him a speedy recovery at this difficult time.”

Foreign Secretary Dominic Raab has been standing in for the prime minister since Monday night and has been leading “war cabinet” meetings around the government’s response to COVID-19. At a press briefing Tuesday evening, Raab described Johnson as a “fighter” and said he had complete “confidence” in Johnson’s plans, noting “total unity and total resolve on implementing them.”

It was first revealed that Johnson had coronavirus on March 27, and though he has been working from his residence, a persisting cough and fever prompted his admission to hospital on Sunday.

However, Johnson took to Twitter on Monday to update that he was in “good spirits” and keeping in touch with his team, which rendered the ICU development later in the day a shock to the nation.

The U.K. has been hard hit by the coronavirus outbreak, which has so far claimed 6,159 lives. There are 55,242 cases of COVID-19 to date, with numbers steadily rising each day.

Unlike other countries that were quick to implement precautionary measures such as gatherings bans and lockdowns, Johnson’s government was slow to act on such public health safeguards in the U.K. and has struggled in recent weeks to convey the seriousness of the pandemic to the public.

It is thought that the prime minister’s hospitalization and intensive care stay will go some distance in demonstrating the severity of the virus.

While the government had initially said it would review lockdown measures after three weeks, which would have been April 13, it has now extended that review period.