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The coronavirus can stay aloft for hours in tiny droplets in stagnant air, infecting people as they inhale, mounting scientific evidence suggests.

This risk is highest in crowded indoor spaces with poor ventilation, and may help explain superspreading events reported in meatpacking plants, churches and restaurants.

It’s unclear how often the virus is spread via these tiny droplets, or aerosols, compared with larger droplets that are expelled when a sick person coughs or sneezes, or transmitted through contact with contaminated surfaces, said Linsey Marr, an aerosol expert at Virginia Tech.

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Aerosols are released even when a person without symptoms exhales, talks or sings, according to Marr and more than 200 other experts, who have outlined the evidence in an open letter to the World Health Organization.

What is clear, they said, is that people should consider minimizing time indoors with people outside their families. Schools, nursing homes and businesses should consider adding powerful new air filters and ultraviolet lights that can kill airborne viruses.

What does it mean for a virus to be airborne?

For a virus to be airborne means that it can be carried through the air in a viable form. For most pathogens, this is a yes-no scenario. HIV, too delicate to survive outside the body, is not airborne. Measles is airborne, and dangerously so: It can survive in the air for up to two hours.

For the coronavirus, the definition has been more complicated. Experts agree that the virus does not travel long distances or remain viable outdoors. But evidence suggests it can traverse the length of a room and, in one set of experimental conditions, remain viable for perhaps three hours.

How are aerosols different from droplets?

Aerosols are droplets, droplets are aerosols — they do not differ except in size. Scientists sometimes refer to droplets fewer than 5 microns in diameter as aerosols. (By comparison, a red blood cell is about 5 microns in diameter; a human hair is about 50 microns wide.)

From the start of the pandemic, the WHO and other public health organizations have focused on the virus’s ability to spread through large droplets that are expelled when a symptomatic person coughs or sneezes.

These droplets are heavy, relatively speaking, and fall quickly to the floor or onto a surface that others might touch. This is why public health agencies have recommended maintaining a distance of at least 6 feet from others, and frequent hand washing.

But some experts have said for months that infected people also are releasing aerosols when they cough and sneeze. More important, they expel aerosols even when they breathe, talk or sing, especially with some exertion.

Scientists know now that people can spread the virus even in the absence of symptoms — without coughing or sneezing — and aerosols might explain that phenomenon.

Because aerosols are smaller, they contain much less virus than droplets do. But because they are lighter, they can linger in the air for hours, especially in the absence of fresh air. In a crowded indoor space, a single infected person can release enough aerosolized virus over time to infect many people, perhaps seeding a superspreader event.

For droplets to be responsible for that kind of spread, a single person would have to be within a few feet of all the other people, or to have contaminated an object that everyone else touched. All that seems unlikely to many experts: “I have to do too many mental gymnastics to explain those other routes of transmission compared to aerosol transmission, which is much simpler,” Marr said.

Can I stop worrying about physical distancing and washing my hands?

Physical distancing is still very important. The closer you are to an infected person, the more aerosols and droplets you may be exposed to. Washing your hands often is still a good idea.

What’s new is that those two things may not be enough. “We should be placing as much emphasis on masks and ventilation as we do with hand washing,” Marr said. “As far as we can tell, this is equally important, if not more important.”

Should I begin wearing a hospital-grade mask indoors? And how long is too long to stay indoors?

Health care workers may all need to wear N95 masks, which filter out most aerosols. At the moment, they are advised to do so only when engaged in certain medical procedures that are thought to produce aerosols.

For the rest of us, cloth face masks will still greatly reduce risk, as long as most people wear them. At home, when you’re with your own family or with roommates you know to be careful, masks are still not necessary. But it is a good idea to wear them in other indoor spaces, experts said.

As for how long is safe, that is frustratingly tough to answer. A lot depends on whether the room is too crowded to allow for a safe distance from others and whether there is fresh air circulating through the room.

What does airborne transmission mean for reopening schools and colleges?

This is a matter of intense debate. Many schools are poorly ventilated and are too poorly funded to invest in new filtration systems. “There is a huge vulnerability to infection transmission via aerosols in schools,” said Don Milton, an aerosol expert at the University of Maryland.

Most children younger than 12 seem to have only mild symptoms, if any, so elementary schools may get by. “So far, we don’t have evidence that elementary schools will be a problem, but the upper grades, I think, would be more likely to be a problem,” Milton said.

College dorms and classrooms are also cause for concern.

Milton said the government should think of long-term solutions for these problems. Having public schools closed “clogs up the whole economy, and it’s a major vulnerability,” he said.

“Until we understand how this is part of our national defense, and fund it appropriately, we’re going to remain extremely vulnerable to these kinds of biological threats.”

What are some things I can do to minimize the risks?

Do as much as you can outdoors. Despite the many photos of people at beaches, even a somewhat crowded beach, especially on a breezy day, is likely to be safer than a pub or an indoor restaurant with recycled air.

But even outdoors, wear a mask if you are likely to be close to others for an extended period.

When indoors, one simple thing people can do is to “open their windows and doors whenever possible,” Marr said. You can also upgrade the filters in your home air-conditioning systems, or adjust the settings to use more outdoor air rather than recirculated air.

Public buildings and businesses may want to invest in air purifiers and ultraviolet lights that can kill the virus. Despite their reputation, elevators may not be a big risk, Milton said, compared with public bathrooms or offices with stagnant air where you may spend a long time.

If none of those things are possible, try to minimize the time you spend in an indoor space, especially without a mask. The longer you spend inside, the greater the dose of virus you might inhale.

New Delhi, Feb 14: Senior Congress leader P Chidambaram on Thursday said there must be a "huge mass movement" if any Muslim was sent to detention camps in case the Supreme Court upheld the validity of the Citizenship Amendment Act (CAA).

Speaking at the JNU campus, the former Union minister said the CAA was an outcome of the "NRC fiasco" in Assam that left 19 lakh people out of the document.

The CAA was brought to accommodate the 12 lakh Hindus among the 19 lakh people who could not be included in the National Register of Citizens (NRC) in Assam, he claimed.

Replying to a question by a student on the best course of action if the CAA was upheld by the apex court, Chidambaram said, "When they touch the excluded...they will only be Muslims, to identify and throw them out, declare them stateless, there must be a huge mass movement, resisting any Muslim being thrown out or kept in detention camps."

He also said the Congress believed that the CAA must be repealed and there should be a political struggle so that the National Population Register (NPR) was pushed beyond 2024.

Claiming that the NRC, CAA and NPR were "closely connected" to each other, Chidambaram said, "The CAA was brought due to the NRC fiasco in Assam and the opposition to the CAA gave way to the NPR."

He asserted that the Congress was protesting against the CAA and the NRC across the country, but had consciously avoided going to Shaheen Bagh, as in that case, the ruling Bharatiya Janata Party (BJP) would brand the demonstration against the amended citizenship law as a "political" one.

"See, we are not going to Shaheen Bagh because that would be falling into the BJP's trap. If we go there, they (BJP) will say it is political," the senior Congress leader said.

Slamming the CAA and the NRC as instruments undermining the very basis of the formation of India, he said the country, instead, needed a "broad law" on refugees.

Speaking at an event against the NRC, CAA and NPR hosted by the Congress's student wing, NSUI, at the Jawaharlal Nehru University (JNU), Chidambaram accused the BJP of spreading lies against Opposition parties.

"The BJP says the Congress, the Left and other liberal parties are against citizenship to persecuted Hindus, Sikhs from Pakistan, Bangladesh. But we are not against those included, our opposition is against exclusion," he said.

Questioning the rationale behind the CAA, the former finance minister said it excluded people on the basis of religion.

"Why only three countries, what about other neighbouring countries — Nepal, Bhutan, China? What about others treated much worse? The Ahmadiyas and Shias of Pakistan, the Rohingyas of Myanmar, Tamil Hindus are equally persecuted, why are they left out?" he questioned.

Chidambaram also said the CAA did not cover persecution based on language, political ideology and economic deprivation.

Slamming the NRC, he wondered which country would accept those left out of the document.

"Which country is going to accept them? How will they go? Where will you send them? (Home Minister) Amit Shah saying that they are termites and he will throw them out by 2024 is talking through his hat," the senior Congress leader said.

New Delhi, May 6: The Central Board of Indirect Taxes and Customs (CBIC) has extended the validity of electronic way (E-way) bills, whose expiry date fell between March 20 and April 15, till May 31.

"Notification No. 40/2020-Central Tax issued to extend the validity of e-way bills till May 31 for all those e-way bills which were generated on or before March 24, 2020 and had expiry between the period from March 20 to April 15, 2020," the CBIC tweeted on Tuesday.

E-way bill is produced by transporters and businessmen before a Goods and Services Tax (GST) inspector for moving goods worth over Rs 50,000 from one state to another.