Coronavirus is likely to keep spreading for at least another 18 months to two years -- until 60 percent to 70 percent of the population worldwide has been infected, a team of longstanding pandemic experts predicted Thursday in a new report.

They recommended that the United States prepare for a worst-case scenario that includes a second big wave of coronavirus infections in the fall and winter. Even in a best-case scenario, people will continue to die from the virus, they predicted.

“This thing’s not going to stop until it infects 60 to 70 percent of people,” Michael Osterholm, who directs the Center for Infectious Disease Research and Policy at the University of Minnesota, told CNN. “The idea that this is going to be done soon defies microbiology.”

Osterholm has been writing about the risk of pandemics for 20 years and has advised several presidents.

Because Covid-19 is new, no one has any immunity, the report said. “The length of the pandemic will likely be 18 to 24 months, as herd immunity gradually develops in the human population.”