Lifting social-distancing measures all at once could risk simply delaying the epidemic’s peak and potentially making it more severe, the scientists warned in an article published Tuesday in the journal Science.

The course of the pandemic will depend on questions not yet answered: Will the virus’s spread change with the seasons? What immunity will people have after they’re infected? And does exposure to coronaviruses that cause mild illnesses confer any protection against the pathogen that causes COVID-19?

Those questions are being weighed by government leaders who have seen economies around the globe come to a standstill because of the social-distancing measures. With millions of people out of work and staying home, pressure is growing to loosen restrictions in the U.S. and elsewhere. Doing so, experts have said, will depend on having in place measures to control the disease, such as widespread testing.

The Harvard researchers used computer models to simulate how the pandemic might play out. One possibility is that strict social distancing followed by intensive public-health detective work could chase down and eradicate the virus. That’s what happened with SARS-CoV-1, which caused a 2003 outbreak. But with confirmed cases of the new pathogen approaching 2 million globally, that outcome is seen as increasingly unlikely, the researchers wrote.

Seasonal illness

More likely is that the virus is here to stay like influenza, traveling the globe seasonally. In one model, 20 weeks of measures to limit spread were followed by an epidemic peak that was as great as an uncontrolled spread.

“The social distancing was so effective that virtually no population immunity was built,” the researchers said of that scenario. If the virus is more transmissible in colder months, delaying the peak into the autumn could exacerbate the strain on health-care systems, they wrote.

To avoid such outcomes, on-and-off social distancing measures might be needed until 2022, unless hospital capacity is increased, or effective vaccines or treatments are developed.

The authors don’t endorse a particular path forward but said they sought “to identify likely trajectories of the epidemic under alternative approaches.”

More coronavirus coverage from Fortune:

—How Fortune 500 companies are utilizing their resources and expertise during the pandemic
—Inside the surreal “Mask Economy”: Price-gouging, bidding wars, and armed guards
—When will stimulus checks be deposited or mailed? Ensure yours is not delayed
—Job hunting during a pandemic: How laid-off tech workers are faring
—How South Korea is preparing for the first nationwide election of the coronavirus era
—We need to protect whistleblowers as the coronavirus opens the door for bad actors
—There are 32 authorized coronavirus tests so far—here’s how they differ
—PODCAST: COVID-19 might have upended the concept of the best companies of the year
—VIDEO: 401(k) withdrawal penalties waived for anyone hurt by COVID-19

Subscribe to Outbreak, a daily newsletter roundup of stories on the coronavirus pandemic and its impact on global business. It’s free to get it in your inbox.