NYT — Prime Minister Boris Johnson was hospitalized on Sunday evening after 10 days of battling the coronavirus, unnerving a country that had gathered to watch Queen Elizabeth II rally fellow Britons to confront the pandemic and reassure them that when the crisis finally ebbed, “we will meet again.”

The British government said that Mr. Johnson would be undergoing tests and that he would continue to carry out his duties.

But the uncertainty generated by his persistent illness underscored the sense of crisis that led the queen to address the country in a rare televised speech that evoked the darkest days of World War II.

“I am speaking to you at what I know is an increasingly challenging time,” the queen said. “A disruption that has brought grief to some, financial difficulties to many, and enormous changes to the daily lives of us all.”

Her remarks were taped at Windsor Castle, where she has sequestered herself against a virus that has infected at least 40,000 people in Britain, including her eldest son and heir, Prince Charles, and other senior British officials besides Mr. Johnson.

Speaking in terms both personal and historical, the queen likened the enforced separation of Britain’s lockdown to the sacrifices families made during World War II, when parents sent away their children for their own safety. She urged a country that has approached these measures with some nonchalance to commit itself to the cause.

“Today, once again, many will feel a painful sense of separation from their loved ones,” the queen said. “But now, as then, we know, deep down, that it is the right thing to do.”

Before being transferred to the hospital, Mr. Johnson, 55, had been in isolation in his apartment next door to 10 Downing Street, where officials said he was running a high temperature. Early last week, Mr. Johnson’s aides said they expected him to end his self-isolation on Friday. But he still looked visibly weakened when he made a statement in a video late in the week.

The queen’s speech was only the fourth time in her 68-year reign in which she has addressed the British people, apart from her annual Christmas greeting — and it carried a distinct echo of the celebrated radio address her father, George VI, delivered in September 1939, as Britain stood on the brink of war with Germany.

Like the king eight decades ago, the queen appealed to the quintessential British traits of stoicism and solidarity, and explicitly linked the pandemic to the war as a defining moment for modern Britain. This time, she said, the country needs to come together to vanquish an enemy that brings death not in the terrifying bombing raids of the Blitz but in the ordinary encounters of people transmitting a dangerous pathogen.