A top public health expert on Monday cautioned U.S. officials against prematurely lifting restrictions imposed to curb the spread of the coronavirus, saying that doing so could result in millions of deaths.

The warning from Tom Inglesby, the director of the Center for Health Security at the Johns Hopkins Bloomberg School of Public Health, came as President Donald Trump said during a press conference that he was considering easing social distancing guidelines after March 30.

“We’re not going to let the cure be worse than the problem,” Trump said, noting how badly virus-induced measures have impacted businesses and workers.

But Inglesby, in a series of tweets, laid out just how bad the problem could get.

“Anyone advising the end of social distancing now, needs to fully understand what the country will look like if we do that,” Inglesby wrote. “COVID would spread widely, rapidly, terribly, could kill potentially millions in the yr ahead with huge social and economic impact across the country.”

Many models report that health care systems will be completely overwhelmed/collapse by the peak of cases if major social distancing is not put in place. 12/x — Tom Inglesby (@T_Inglesby) March 23, 2020

Anyone advising the end of social distancing now, needs to fully understand what the country will look like if we do that. COVID would spread widely, rapidly, terribly, could kill potentially millions in the yr ahead with huge social and economic impact across the country. 15/x — Tom Inglesby (@T_Inglesby) March 23, 2020

In the U.S., there have been over 46,000 confirmed cases of COVID-19, the disease caused by the virus, and at least 590 deaths, according to data compiled by Johns Hopkins University. A week ago, there were just 5,000 or so confirmed cases in the country.

“Some hospitals have said publicly that within a week they will not have ventilators to treat everyone with COVID anymore,” Inglesby tweeted. “There continue to be big diagnostic limitations. ... There continues to be terrible shortages in the masks that health care workers need to keep from getting sick with this disease.”

How do we reduce the speed of spread in the U.S. and how do we lower the odds that intensive care units in hospitals will run out of supplies? Large-scale social distancing, Inglesby wrote.

He warned that social distancing measures take weeks to work, as seen in China, and noted that the U.S. was only about 7-10 days into this process as of Monday. At least 16 states, including California, Louisiana and New York, have issued “stay at home” orders. At least four others have implemented similar restrictions in certain parts of the state.

“To drop all these measures now would be to accept that COVID [patients] will get sick in extraordinary numbers all over the country, far beyond what the US health care system could bear,” Inglesby wrote. “Many models report that health care systems will be completely overwhelmed/collapse by the peak of cases if major social distancing is not put in place.”

He warned that COVID-19′s fatality rate could surge in such a scenario because hospitals would struggle to provide care for the 15% of patients expected to be severely ill due to the virus.

Social distancing guidelines, recommended by medical professionals and top U.S. public health officials, are necessary to prevent the spread of the virus. For example, China has reported few new local infections in the last week after two months of imposing strict social distancing orders.

Italy, on the other hand, failed to impose such draconian measures as the virus began to spread within its borders. Now, the Italian health care system is overwhelmed with more than 63,000 confirmed cases across the country and more than 6,000 deaths. Because there are not enough ventilators available, Italian doctors are forced to essentially decide who lives and who dies.

Italians, who have been on lockdown since March 9, have urged Americans to take the virus seriously and stay at home to avoid a similar outcome.

“Before considering big changes to social distancing measures now, we should as quickly as possible get to strongest possible position for COVID response ― we’re nowhere near that now,” Inglseby wrote.

The U.S. must take several steps, including rapidly increasing the production of supplies, such as medical masks and ventilators, as well as significantly reducing the number of COVID-19 cases so those infected can be appropriately isolated, he said.

“Once we have those things in place, it would be a far less risky time to take stock of social distancing measures in place and consider what might gradually be reduced with trial and error,” Inglesby tweeted.

In that scenario, he said, there would still need to be a “science informed dialogue about which businesses need to be closed vs what can stay open in some way if social distancing can be put in place in them.”

“But we need to press ahead for now [with] closed schools, mass telecommuting, no gatherings, strong advisory to stay home unless you need to go out,” Inglesby wrote. “All are needed to slow this epidemic.”