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We’ve reached the coronavirus plateau. So when will the numbers begin to decline?

A Cataldo ambulance left MGH and traveled underneath a sign on the highway in Boston.
A Cataldo ambulance left MGH and traveled underneath a sign on the highway in Boston.Jessica Rinaldi/Globe Staff

The coronavirus pandemic in Massachusetts appears to be plateauing, raising the question: When are the numbers going to come down and how fast? Experts are concerned that it could take longer than we expect.

“We don’t know how far along the plateau we are,” said William Hanage, an assistant professor of epidemiology at Harvard T.H. Chan School of Public Health.

Governor Charlie Baker has said he is not seeing improvements in key measures that he is scrutinizing for clues to when it will be safe to reopen the economy. With the death toll rising to more than 3,000 this week, Baker announced Tuesday that he was extending his non-essential business closure order and stay-at-home advisory until May 18.

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Describing a straight line on a graph with his hand, Baker said at a State House news conference, “We’ve been like this for a while.”

Baker focused on hospitalizations and ICU admissions, saying, “We’ve basically been flat for 12 days. We’re flat at a high level. But 12 days, 13 days counting today -- you’re not going to find a lot of other places that just sit like this for 13 days.”

Data released by the state Department of Public Health Tuesday showed that in the two weeks from April 13 to Monday the number of hospitalizations climbed from more than 3,400 to nearly 4,000 last Tuesday. For the next six days, it lingered in the mid- to high 3,800s.

Experts have said that the first sign of victory in the fight against coronavirus will be a decline in new cases over several consecutive weeks, even as testing expands. That decline has not materialized yet. A week or two after the case decline, new coronavirus-related hospitalizations should fall, in light of the time it takes for the disease to progress.

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Samuel Scarpino, an epidemiologist at Northeastern University. said he expected hospitalization and case numbers to come down soon, but he warned that it would just be “signs that we’re past the peak,” and not a signal to immediately reopen the economy.

He said it was particularly important to leave social distancing measures in place until hospitalization and death numbers decline because they reflect the burden on the health care system, which has been under stress because of the pandemic.

Hanage and other experts are worried that the plateau might be longer than expected because in the United States, social distancing restrictions have not been as stringent as in Wuhan, China, where the pandemic began and a strict lockdown was put in place.

“The nature of the first surge of the pandemic will reflect the actions that a community takes to stop new infections. If they are stopped very quickly by very intense actions and quarantines as was the case in Wuhan, then you expect new cases to fall rapidly. However if less intense interventions are put in place the virus can continue to transmit, just more slowly. This can lead to a long plateau in which cases decline, but over a longer time period,” Hanage said in an e-mail statement.

“We do know that it could be worse," Hanage added.

Robert Hecht, a Yale University epidemiology professor and president of Boston-based Pharos Global Health Advisors, said, “I think we’re going to see this really slow decline … not that steep downhill run that we’re all looking for."

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“I think we could have done better and we still could,” he said.

Former FDA Commissioner Scott Gottlieb, who has been advising Baker, has also warned of a long downward slope nationally.

In a series of tweets Sunday, he said that, while the nation might have hit a plateau, “Our mitigation steps were not as stringent as China’s, they were leakier, and our epidemic was far more pervasive across our country. We’re likely to see a much slower decline in new cases spread across weeks not days. While there are signs of U.S. improvement, it’ll be slow.”

“We all want this to be over. And things are mostly trending in the right direction. But we’re still very much in the thick of the epidemic. What we do over the next few weeks will determine if we can get this wave more firmly behind us, or whether covid remains a combustible threat,” he said.

He said that some models, like a closely watched model from the University of Washington Institute for Health Metrics and Evaluation, predict a steep decline like the one that has been seen in China, but he suggested the US was likely to follow a more gradual slope, similar to what has happened in Italy.

“We’re not out of the woods,” he said.

Travis Andersen of the Globe staff contributed to this report.



Martin finucane can be reached at martin.finucane@globe.com.