The U.K.’s coronavirus outbreak is likely to last into next spring and hospitalize up to 7.9 million people, according to a secret briefing for senior National Health Service (NHS) officials by Public Health England.

“As many as 80% of the population are expected to be infected with Covid-19 in the next 12 months, and up to 15% (7.9 million people) may require hospitalization,” the document, first obtained by The Guardian, states.

The chief medical adviser to the U.K.’s government, Prof. Chris Whitty, had previously described 80 percent as a worst-case scenario, but the document viewed by the newspaper presents it as an expected outcome.

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“For the public to hear that it could last for 12 months, people are going to be really upset about that and pretty worried about that,” Paul Hunter, a professor of medicine at the University of East Anglia and a specialist in epidemiology, told the newspaper.

“A year is entirely plausible. But that figure isn’t well appreciated or understood,” he added. “I think it will dip in the summer, towards the end of June, and come back in November, in the way that usual seasonal flu does. I think it will be around forever, but become less severe over time, as immunity builds up.”

The report also projects that about 500,000 of the 5 million workers deemed essential to keep vital services and infrastructure running will need to take sick time at any given month-long period. About one-fifth of the 5 million are NHS staff.

The nation has confirmed 1,391 cases of the virus and 350 deaths as of Monday morning. Prime Minister Boris Johnson last week called on anyone with a cough to self-isolate for seven days.