The rule of thumb, or rather feet, has been to stand six feet apart in public. That’s supposed to be a safe distance if a person nearby is coughing or sneezing and is infected with the novel coronavirus, spreading droplets that may carry virus particles.

And scientists agree that six feet is a sensible and useful minimum distance, but, some say, farther away would be better.

Six feet has never been a magic number that guarantees complete protection. The Centers for Disease Control and Prevention, one of the organisations using that measure, bases its recommendation on the idea that most large droplets that people expel when they cough or sneeze will fall to the ground within six feet.

But some scientists, having looked at studies of air flow and being concerned about smaller particles called aerosols, suggest that people consider a number of factors, including their own vulnerability and whether they are outdoors or in an enclosed room, when deciding whether six feet is enough distance.

Sneezes, for instance, can launch droplets a lot farther than six feet according to a recent study.

No scientists are suggesting a wholesale change in behaviour, or proposing that some other length for separation from another human, like seven, or nine feet, is actually the right one.

“Everything is about probability,” said Dr Harvey Fineberg, who is the head of the Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats at the National Academies of Sciences, Engineering and Medicine. “Three feet is better than nothing. Six feet is better than three feet. At that point, the larger drops have pretty much fallen down. Maybe if you’re out of spitting range, that could be even safer, but six feet is a pretty good number.”

One complicating factor is that aerosols, smaller droplets that can be emitted when people are breathing and talking, play some role in spreading the new coronavirus. Studies have shown that aerosols can be created during certain hospital or laboratory procedures like when using nebulisers to help patients inhale medication, which makes such procedures risky for doctors who do them.

If the aerosols that people exhale in other settings are significant in spreading the disease, the six-foot distance would not be completely protective because those are carried more easily by air currents.

Aerosols are generally considered to be particles under 5 microns in diameter about the size of a red blood cell, and can be spread in the environment by talking and breathing. But some researchers argue that this is a false dichotomy. Infectious droplets can’t easily be divided into those that are big enough to fall to the ground quickly and those that stay aloft because so much depends on environmental conditions and how deeply they penetrate into the respiratory tract.

“It’s really a continuum,” said Dr Donald Milton, who studies bioaerosols at the University of Maryland School of Public Health.

Even without the launching power of a sneeze, air currents could carry a flow of aerosol sized virus particles exhaled by an infected person 20 feet or more away.

“In any confined geometry like an office room, meeting room, department store, food store,” said Eugene Chudnovsky, a physicist at the City University of New York. In a study not yet peer reviewed, he analysed air flow and showed how, “the vortices in the air are taking the virus to different places”.

A preliminary study at the University of Nebraska Medical Center found evidence of coronavirus genetic material on various surfaces in isolation rooms where infected patients were being treated, including on air vents more than six feet from the patients. The research, which has not yet been peer reviewed, indicates that the virus can occasionally travel long distances.

“The virus is so small, it can hitch a ride even on tiny, tiny particles,” Dr Fineberg said. “But how important is each size and how well they can transmit disease is not fully understood.”

It is also unclear how many virus particles it takes to start an infection, how long the viral particles remain viable or if studies like the one in Nebraska simply detected the genetic calling card the virus left behind.

Spacing is an effective solution because it also reduces the number of people in a confined space. That reduces the likelihood of an infected person being in the group. And if there is one, fewer other people might be infected.

Dr Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said the six-foot distance would clearly “reduce the number of droplets you come in contact with. I have no doubt about that”.

But, he said: “The question is what does it take for you to get infected? And that I think is the trillion-dollar question we have.”

He said, “Maybe all it takes is an aerosol. You don’t need any droplets at all.” If that’s the case, he said, then someone who is at high risk would not want to be in the same room with someone who is infected or might be infected.

Current guidelines already suggest that anyone at high risk should stay home and not be out in public in the first place. And they seem to be working. Places where people reduced travel and started social distancing weeks ago, especially in California, New York and Washington, are starting to show a reduction in the number of new coronavirus cases.

People still need to shop and take care of necessities, Dr Osterholm said, but reducing the risk of exposure to all possible modes of transmission — infected surfaces, droplets and smaller aerosols — is important.

“Your job is to limit it as much as you can.”

Changing medicine

Just about a month ago, people stricken with the new coronavirus started to arrive in unending ranks at hospitals in the New York metropolitan area, forming the white-hot centre of the pandemic in the US.

Now, doctors in the region have started sharing on medical grapevines what it has been like to re-engineer, on the fly, their health care systems, their practice of medicine, their personal lives.

Doctors, if you could go back in time, what would you tell yourselves in early March?

“What we thought we knew, we don’t know,” said Dr Nile Cemalovic, an intensive care physician at Lincoln Medical Center in the Bronx.

Medicine routinely remakes itself, generation by generation. For the disease that drives this pandemic, certain ironclad emergency medical practices have dissolved almost overnight.

The biggest change: Instead of quickly sedating people who had shockingly low levels of oxygen and then putting them on mechanical ventilators, many doctors are now keeping patients conscious, having them roll over in bed, recline in chairs and continue to breathe on their own — with additional oxygen — for as long as possible.

The idea is to get them off their backs and thereby make more lung available. A number of doctors are even trying patients on a special massage mattress designed for pregnant women because it has cutouts that ease the load on the belly and chest.

Other doctors are rejiggering CPAP breathing machines, normally used to help people with sleep apnea, or they have hacked together valves and filters. For some critically ill patients, a ventilator may be the only real hope.

Then there is the space needed inside buildings and people’s heads.

In an instant, soaring atrium lobbies and cafeterias became hospital wards; rarelyused telemedicine technology has suddenly taken off, and doctors are holding virtual bedside conferences with scattered family members; physicians force themselves to peel away psychically and emotionally from fields of battle where the opponent never observes the ceasefire that the rest of society has entered.

More than 12,000 people have died with coronavirus in Connecticut, New Jersey and New York, where there are more than 260,000 confirmed cases. Those numbers almost certainly understate the casualties, officials acknowledge, as testing of both the living and the dead remains spotty.

The New York-area doctors have not uncovered any surefire way to fight Covid-19 — the disease caused by the virus — and not enough time has passed to say if their improvisations will hold up, said Dr Anand Swaminathan, an assistant clinical professor of emergency medicine at St Joseph’s University Medical Center in Paterson, New Jersey.

No one knows if any of the spaghetti will stick to the wall.

“I’m confident that we will have a lot of answers in months,” said Dr Reuben Strayer, an emergency medicine physician at Maimonides Medical Center in Brooklyn. “Unfortunately, that doesn’t help us right now. You have to start somewhere.”

“Never in my life have I had to ask a patient to get off the telephone because it was time to put in a breathing tube,” said Dr Richard Levitan, who recently spent 10 days at Bellevue Hospital Center in Manhattan.

Why is this so odd? People who need breathing tubes, which connect to mechanical ventilators that assist or take over respiration, are rarely in any shape to be on the phone because the level of oxygen in their blood has declined precipitously.

If conscious, they are often incoherent and are about to be sedated so they do not gag on the tubes. It is a drastic step.

Yet many Covid-19 patients remain alert, even when their oxygen has sharply fallen, for reasons health care workers can only guess.

(Another important signal about how sick the patients are from Covid-19 — the presence of inflammatory markers in the blood — is not available to physicians until laboratory work is done.)