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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 11: Cheaper lending rates in the country along with the government's booster via tax cuts seem to have had little effect on vehicle sales in January, with car sales decreasing by over 14,531 units, or slightly over 8 per cent, compared to January last year.

According to Rajan Wadhera, President of industry body Society of Indian Automobile Manufacturers (SIAM), which gives out the auto sales numbers, the overall slump in vehicle sales in India was due to the "rising cost of vehicle ownership and slower growth in GDP".

Barring three-wheelers, all other segments showed de-growth.

Vehicle sales across segments have been declining for over a year now. SIAM sales data last month compared with that of January 2019 showed that domestic passenger vehicle sales slipped 6.2 per cent to 262,714 units. The decline in car sales stood at 8.1 per cent, and two-wheelers 16.06 per cent.

Sales of commercial vehicles, an indicator of industrial health in the economy, slipped by 14.04 per cent to 75,289 units last month, while the vehicle sales across categories registered a de-growth of 13.83 per cent to 17,39,975 units from 20,19,253 units in January 2019, SIAM said.

However, Wadhera said, they were hopeful that recent government announcements on infrastructure and rural economy would support growth of vehicle sales, especially in the commercial and two-wheeler segments.

"We are looking forward to the early announcement of an incentive-based scrappage policy in the context of the recent assurances by the government," Wadhera said.

New Delhi, Jan 31: The Supreme Court Friday dismissed the plea filed by one of the four death row convicts in the Nirbhaya gang-rape and murder case, Pawan Gupta, seeking review of its order rejecting his juvenility claim.

The review plea filed earlier in the day was taken up for consideration in-chamber by a bench comprising Justices R Banumathi, Ashok Bhushan and A S Bopanna. 

On January 20, the apex court had rejected the plea by Pawan who had challenged the Delhi High Court's order dismissing his juvenility claim.

Advocate A P Singh, who is representing Pawan in the case, said he filed a petition on his behalf seeking review of the top court's January 20 order on Friday.

While dismissing the plea, the top court had said there was no ground to interfere with the high court order that rejected Pawan's plea and his claim was rightly rejected by the trial court as also the high court.

It had said the matter was raised earlier in the review petition before the apex court which rejected plea of juvenility taken by Pawan and another co-accused Vinay Kumar Sharma and that order has attained finality.

Singh had argued that as per his school leaving certificate, he was a minor at the time of the offence and none of the courts, including trial court and high court, ever considered his documents.

Solicitor General Tushar Mehta, appearing for the Delhi Police, had said Pawan's claim of juvenility was considered at each and every judicial forum and it will be a travesty of justice if the convict is allowed to raise the claim of juvenility repeatedly and at this point of time.

The trial court on January 17 issued black warrants for the second time for the execution of all the four convicts in the case -- Mukesh Kumar Singh (32), Pawan (25), Vinay (26) and Akshay (31) -- in Tihar jail at 6 am on February 1. Earlier, on January 7, the court had fixed January 22 as the hanging date.

As of now, only Mukesh has exhausted all his legal remedies including the clemency plea which was dismissed by President Ram Nath Kovind on January 17 and the appeal against the rejection was thrown out by the Supreme Court on January 29.

Convict Akshay's curative petition was dismissed by the top court on January 30. Another death row convict Vinay moved mercy plea before President on January 29, which is pending.

Singh has also approached the trial court seeking stay on the execution scheduled on February 1, saying the legal remedies of some of the convicts are yet to be availed.

A 23-year-old paramedic student, referred to as Nirbhaya, was gang-raped and brutally assaulted on the intervening night of December 16-17, 2012, in a moving bus in south Delhi by six people before she was thrown out on the road.