Social distancing is working, but when will things return to normal, and what will that look like?

A sign posted at a US Postal Service building in Dorchester reminded postal customers to keep their social distance.David L. Ryan/Globe Staff

With daffodils and magnolia trees in full bloom, the rites of spring have been clouded by a hard truth: No one really knows when life might return to something close to normal, when it might be safe to go back to work or get a drink at a bar.

But epidemiologists are drawing up plans for a glide path out of the purgatory, which they say could start as early as sometime in May.

Their vision of a reopening, however, is unlikely to include crowds at Fenway Park or Symphony Hall anytime soon. Even July 4 on the Esplanade remains in doubt, as do carefree weekends on crowded beaches.

It is, however, conceivable restaurants could seat diners again and stores welcome back customers, albeit with a range of new requirements before anyone enters.

The key to returning to some semblance of normal, they say: testing. More and more testing.

“The more we know about the prevalence of the virus, the closer we’ll get to being able to reopen,” said Michael Mina, an assistant professor of epidemiology at the Harvard T.H. Chan School of Public Health, who serves on a state task force dealing with the coronavirus.

In the coming days, Massachusetts and several other states will begin drawing blood from hundreds of residents around the state to get a clearer understanding of how many have already been infected and now carry antibodies to the virus. That testing — combined with a broader federal effort — should start producing results by the end of April or early May.

If the virus has infected far more people than the 525,000 Americans who have already tested positive, as Mina and others suspect, that would suggest far more people have immunity to the disease, and that it sickens and kills fewer people than feared.

If that proves true, and rigorous social distancing continues, Massachusetts could begin to see the number of newly reported cases dwindle from around 2,000 a day now to about a dozen or fewer a day by the latter half of May, Mina said.

“Once we get it under control, we can start reopening in a safe way,” he said.

Scientists say the pandemic will persist until the virus’s spread is hobbled by “herd immunity,” estimated to occur when at least 80 percent of people are immune, either through a vaccine or infection. It’s unclear how long post-infection immunity lasts.

When asked this week when the state might begin easing the shutdown, Governor Charlie Baker said he would rely on public health officials to make such decisions.

“We’re going to think about what life could be like once we get past this, but I will be incredibly careful about not permitting this insidious, awful, and horribly dangerous and contagious virus from coming back any time soon,” he said. “I get the fact that the consequences of all this are severe. But the reason we’re doing this is to keep people alive, and to keep our health care system from getting so overwhelmed.”

In an interview, Mayor Martin J. Walsh of Boston cautioned residents not to become focused on an early end to social distancing.

“When’s it going to end, none of us know,” he said. “And what it’s going to be like when it ends, no one knows.”

China, which has reached a later stage of the pandemic, offers a window into what a gradually reopened society might look like.

In Beijing, for example, anyone entering a store, office, or apartment building is usually required to have their temperature taken, and infrared cameras are located in many places to also detect fevers. Nearly everyone continues to wear face masks and is required to display special codes on their cellphones that register their medical history.

When asked if Boston might take similar precautions, Walsh noted that anyone now entering City Hall, which remains open two days a week, must have their temperature checked.

He recognizes residents are becoming antsy, and that at some point, the economy will have to reopen. But he said it was too early to discuss specific plans.

“We’re still in the middle of this battle, so I’m not at the point where I can think about what life looks like after this,” Walsh said. “But when we do open, I think we’re going to have a very different society.”

Until there’s a vaccine, one part of life in the coming months will be more testing and isolating anyone with symptoms of the virus, as is now common in South Korea, Singapore, Hong Kong, and Taiwan, epidemiologists say.

Such heightened vigilance will be required to prevent new outbreaks from exploding into larger epidemics.

That’s a central part of a new plan by a team of public health experts at the American Enterprise Institute led by Dr. Scott Gottlieb, former commissioner of the Food and Drug Administration, who has been advising Baker on the crisis.

Gottlieb said this week he expected parts of America would reopen in May and June, but that the virus would continue to spread.

The plan recommends states should relax restrictions only when they reach three milestones: confirmed cases fall for at least 14 days, which is how long the virus can take to cause symptoms; local hospitals can safely treat all coronavirus patients; and the state can test anyone with symptoms.

Afterward, schools and businesses may reopen, but life shouldn’t return to normal. The plan recommends that those who can continue to work remotely should, and that everyone should continue wearing masks in public. Gatherings should be limited to fewer than 50 people. And those older than age 60, or with underlying medical conditions, should “limit time in the community,” unless an effective treatment becomes available.

The plan also advises states to meticulously track testing data and revert to social distancing restrictions and shuttering nonessential businesses if many cases can’t be linked to known cases, infections rise for five days, or if hospitals can no longer safely treat patients.

Dr. Larry Madoff, a senior infectious disease director at the Massachusetts Department of Public Health, said state officials are still considering options, which will include a community surveillance program to help identify and quarantine anyone who has been exposed to someone infected.

“We will be examining strategies that have been utilized in other countries, plus tapping into national experts, including epidemiologists, economists, and the COVID-19 Command Center medical advisory group,” he said in a statement.

In Washington, the Trump administration is also considering its options.

While public health experts have advised President Trump to allow social distancing measures to continue, he said he would make a decision soon about whether to press for more states to restart their economies.

“I’m going to have to make a decision, and I only hope to God that it’s the right decision,” Trump said on Friday during his daily news briefing.

Thomas Tsai, an assistant professor of health policy at the Harvard Global Health Institute, said his best estimate for when businesses might start reopening would be early summer.

Larger gatherings — such as fans going to Fenway Park or moviegoers taking in a feature at the Coolidge Corner Theater — should take place only if a thorough testing and quarantine regime were in place and effective, he said.

“We know there’s a high chance that there could be another recurrence,” he said. “We need to be very careful about how we proceed, and dial up our responses as they’re needed.”

Restaurants, bars, movie theaters, and concert halls will likely need to reduce their capacities to keep people spaced at least 6 feet apart, said Helen Jenkins, a Boston University biostatistics professor.

But events with large crowds, from music festivals to busy beaches, would likely be unsafe, she said.

“The problem with large gatherings is that they can be super-spreading events where large numbers of people can get infected quite quickly,” Jenkins said.

Federal projections have found that lifting restrictions after a month of social distancing measures would lead to a dramatic spike in infections this summer, and a much higher death toll, according to a New York Times report.

The risk of a second wave means any relaxation of restrictions should come in stages, starting small and expanding over months, depending on whether infections rise, said Andrew Noymer, a population health professor at the University of California Irvine.

“You’re trading off lives against businesses,” Noymer said. “There’s no magic formula where we can do this with no collateral damage. It’s just impossible.”

Others were more sanguine about a relatively normal future in the coming months.

Under the right conditions — with new infections near zero and testing widespread — restaurants could conceivably reopen, but patrons would likely be required to wash their hands before entering, said David Hamer, an infectious disease specialist at Boston Medical Center.

The state could also begin encouraging more people to use public transportation, if everyone wears masks and surfaces are cleaned frequently, he said.

For Mina, the hope is that the virus has already infected tens of millions of Americans, without most of them knowing it.

“If that’s the case, the risks of becoming ill are very low,” he said. “That would mean I would feel a lot more comfortable taking my family to a restaurant.”