David L. Ryan/The Boston Globe/Getty Images Medical professionals in the coronavirus-testing tent at Somerville Hospital in Massachusetts on March 18.

Infectious-disease experts aren’t certain how long the coronavirus pandemic will last, but many agree the worst is yet to come for the US.

Last week, the country saw its cases spike more than 40% in just 24 hours. This week, the number of daily cases continues to rise – even as Americans practice social distancing by working from home, limiting outdoor excursions, and staying 6 feet away from one another.

To determine where the US is headed next, 18 infectious-disease-modelling researchers developed forecasts for how the outbreak could evolve in the coming months.

They estimated only 12% of coronavirus cases (including asymptomatic ones) had been reported in the US as of March 15, which would mean about 29,000 infections had gone undiagnosed by that time. The US has reported more than 69,000 cases and over 1,000 deaths as of Thursday.

The average of the researchers’ predictions suggests that the virus could kill about 195,000 people in the US by the end of the year, but that number varies widely depending on the model.

The most extreme model predicted that up to 1.2 million people could die. By comparison, a typical flu season in the US kills between 11,000 and 95,000 people, according to the Centres for Disease Control and Prevention.

Not all the coronavirus deaths that the models predict, however, would necessarily stem from the current outbreak. The researchers said a second wave of infections would likely occur in the fall, sometime between August and December. The chance of this happening is about 73%, they said.

The models account for a wide variety of outcomes

Since February, researchers from the University of Massachusetts Amherst have conducted weekly surveys of 25 infectious-disease experts on the trajectory of the coronavirus outbreak in the US. Eighteen experts’ responses were published in a report on March 18.

The disease modeler who conducted the survey, Thomas McAndrew, said he didn’t ask researchers to account for social-distancing measures in their models, but researchers still had the option.

“I do imagine they must have speculated about how interventions would impact deaths due to COVID-19,” McAndrew told Business Insider.

Sgt. Amouris Coss/U.S. Army National Guard/Handout/Reuters A Department of Health employee trains New York Army National Guard soldiers at a drive-thru coronavirus-testing centre in New Rochelle, New York, on March 14.

One researcher involved in the report – Andrew Lover, an epidemiologist from the University of Massachusetts – told FiveThirtyEight that his model was based on outbreaks in other countries and adjusted for US testing rates and population density.

Overall, the researchers’ models offered a wide variety of outcomes. Some estimated that the CDC had reported more than 20% of COVID-19 cases as of March 15, but others predicted that the agency had identified just 5% of cases. Some predicted that the US could see 1 million deaths by the end of 2020, while others predicted that the death toll would be in the thousands.

Other models predict up to 2.2 million people could die in the US

The New York Times recently used CDC data to model how the how the virus could spread if no actions were taken to stop transmission in the US. The models show that between 160 million and 214 million people could be infected and as many as 200,000 to 1.7 million people could die.

Other models have yielded even more worrisome projections. On March 16, epidemiologists at Imperial College London released forecasts about how social-distancing measures could slow the virus’ spread in the US. They predicted 2.2 million in the US could die if no efforts were made to control the outbreak. Under that scenario, the death toll would peak in late May or early June, and about 81% of the US population would ultimately get infected.

AP Photo/Jacquelyn Martin Staff of Food and Friends, a food-distribution service for people with life-challenging illnesses, practice social distancing on March 16.

But the Imperial College researchers also said three months of social-distancing measures – such as household quarantines, closures of all schools and universities, and the isolation of infected patients – could cut the number of US deaths in half.

Even if all patients were able to receive treatment at hospitals, however, the researchers predicted that about 1.2 million people in the US could die.

Many experts agree that a ‘2nd wave’ is likely

Many viruses tend to spread more easily in cold weather, so it’s possible that cases of the coronavirus could taper off in the summer and ramp up again in the fall. A recent study from researchers in Beijing (which is still awaiting peer review) showed that the contagiousness of COVID-19 declines with each degree of temperature increase and each per cent of humidity increase. And the H1N1 pandemic had two peaks in the US: one in late June and early July and another in late October and early November.

But since this particular coronavirus hasn’t been seen before in humans, scientists aren’t certain whether it will behave the same way. Plus, it’s spreading in places with high temperatures, like Australia.

A second outbreak could also arise after people resume normal activity. The US asked citizens to avoid international travel starting March 19, but opening its borders again could fuel the virus’ spread. The same goes for allowing citizens to return to work or use mass transit.

Researchers at the Chinese Centre for Disease Control and Prevention have already predicted that the outbreak could rebound in China – where new cases have been close to zero for the past week – once residents go back to work and school.

“Data is starting to come in from Hong Kong that stopping containment measures too early can lead to rebound effects,” Elaine Morrato, the dean of the Parkinson School of Health Sciences and Public Health at Loyola University Chicago, told Business Insider. “It is fair to say some form of social distancing will be required until we have a vaccine or effective treatment identified.”

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