British Prime Minister Boris Johnson is said to be in stable condition and "good spirits", after he was hospitalized in an intensive care unit due to a deterioration of his COVID-19 symptoms. Johnson -- the first leader of a major world power to suffer so drastically from coronavirus complications -- received oxygen support at London's St Thomas's hospital, but has not required ventilation.

55-year-old Johnson was first admitted to hospital on Sunday night (April 5), after suffering from a high temperature and a cough, for over 10 days.

Downing Street says that his condition worsened rapidly over 24 hours.

Johnson’s personal battle with the virus comes as the country enters what scientists say is likely to be one of the most deadly weeks of the pandemic.

Over 5,300 people have so far died in Britain.

The UK doesn’t actually have a formal line of succession should a prime minister become incapacitated, but in the days prior Johnson had asked Foreign Secretary Dominic Raab to deputize for him "where necessary." Even when Johnson was in hospital on Monday (April 6), Raab told a news conference that the PM was still in charge.

But now Raab stands at the helm -- starting with a COVID-19 emergency response meeting on Tuesday morning.

Also on Tuesday, it was reported that another member of Johnson's team, Cabinet Minister Michael Gove, is self isolating as a member of Gove's family is showing symptoms.