U.K. Prime Minister Boris Johnson gave a sober address Thursday on his country's response to the coronavirus, saying "many more families are going to lose loved ones before their time."

The big picture: Johnson said the world was now facing "the worst public health crisis in a generation." His science advisers said the country was now moving from the "contain" phase to the "delay" phase — trying to spread the outbreak over a longer period and protect those most at risk of dying.

What he's saying: "Some people compare it to seasonal flu, alas that is not right. Owing to the lack of immunity, this disease is more dangerous," Johnson said. "It's going to spread further."

He said the true number of cases was "higher, perhaps much higher" than what had been confirmed through testing.

He asked that anyone experiencing a "new, continuous cough" or a high temperature remain at home for seven days.

Johnson did not announce cancellations of large public events like sports games, but he said that step could be taken soon. He was challenged by reporters on why he was not following other countries in taking such steps.

Experts who spoke after Johnson made several key points: