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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.

Kolkata, Jun 19: The nationwide clamour for boycott of Chinese goods is getting louder amid the Ladakh face-off, with traders urging the Centre to direct e-commerce firms to restrict the sale of items from the Dragonland, which imports products worth USD 74 billion to India annually.

Of the total import from China, retail traders sell goods worth around USD 17 billion, mostly comprising toys, household items, mobiles, electric and electronic goods and cosmetics among other things, which could possibly be replaced by Indian products, a national trading body said.

"We, at 'Federation of All India Vyapar Mandal', are advising our members to clear their stocks of Chinese products and refrain from placing fresh orders. We are also requesting the government to restrict e-commerce companies from selling Chinese products," V K Bansal, the association's general secretary, told PTI.

Sushil Poddar, the president of the Confederation of West Bengal Traders Association, said its members have been told to shun trading in Chinese goods as much as possible.

Another national traders' body, The Confederation of All India Traders (CAIT), has decided to step up its movement against the boycott of Chinese goods, under its campaign 'Bhartiya Samaan-Hamara Abhimaan'.

It released a list of over 450 broad categories of commodities, comprising 3,000 Chinese products.

New Delhi, Feb 5: Taking on Delhi Chief Minister Arvind Kejriwal after Shaheen Bagh shooter Kapil Baisala was identified as an AAP worker by police, BJP chief J P Nadda on Tuesday said it exposed the party and Kejriwal who were playing with the country's security.

The Aam Aadmi Party hit back, questioning the police investigation.

In a series of tweets, Nadda said people of the country and Delhi today have seen the "dirty face" of AAP.

"For political longing, Kejriwal and his people even sold the security of the country. Earlier, Kejriwal used to insult the Army and advocate terrorists, but today relations with those who carry out their terrorist activities came to light," he said.

Nadda said he wanted to make it clear to Kejriwal that this country is bigger than any election, any government, and "this nation will not forgive those who play with its security. Kejriwal and his entire team have been exposed. The people of Delhi will give a befitting reply".

He claimed the entire country has seen "photos of Imam Hussain, the MLA and former minister of the Delhi government, with a radical terrorist organisation, PFI".

Days before Delhi goes to polls, police claimed that Baisala is a member of the Aam Aadmi Party. They said Baisala joined the party in early 2019 along with his father.

Police said it had photos of Baisala purportedly joining AAP along with his father Gaje Singh last year.

AAP's Rajya Sabha MP Sanjay Singh alleged that photos which were part of investigation were leaked to the BJP. He also said the party will approach the Election Commission to raise this issue, which has cropped up four days before the polling date.

"On whose instance, the police is giving statement? How did the photos which were part of the investigation reach the BJP? Before the news came out, Manoj Tiwari in the morning stated that the accused was from AAP. How did Manoj Tiwari get this news," Singh questioned in a press conference.

Union minister and BJP's in-charge for the Delhi polls, Prakash Javadekar, in a press conference alleged that "their (AAP's) designs are very clear from the beginning and they are trying every trick".

The whole conspiracy of AAP is to "divide society, cause fear in a community and create a vote bank," he charged.

Javadekar also claimed that photos of Baisala were recovered by police from his mobile phone although they were erased.

He also claimed that Baisala and his father were welcomed by Sanjay Singh at their joining of AAP.

"This proves AAP misleads youth and pushes them on the wrong path. AAP's strategy is to divide two communities, they want to instigate riots in Delhi," Javadekar alleged.

He further alleged that AAP leader Sanjay Singh had said violence would take place in Delhi. Their "conspiracy has been exposed by Delhi Police," he claimed.

"We condemn this politics of AAP," he said.

Javadekar also claimed this was "not an isolated incident" as AAP member Amanatullah Khan made a "very provocative speech" and the party supported Shaheen Bagh and did not give permission for the prosecution of members of the "tukde-tukde gang".

He hinted the BJP could approach the Election Commission against AAP over the issue.