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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.

Bharuch, Mar 5: Vijay Kumar, a resident of the Tamil Nadu has sought help from his friend Abdulkhuda Mohd Hanif Shaikh who is residing in Gujarat to build a temple in his village.

Abdulkhuda Mohd Hanif Shaikh, who also belongs to Tamil Nadu's Paraipatti village and has been residing in Gujarat' Bharuch for a decade has collected Rs 3 lakh from his friends as a donation to build the temple in Paraipatti village in Dindigul district.

"They'd told me 4 months ago and came to me 10 days back. From Vapi to Mehsana, there are several Madrasis, even here in the village too. I personally went to them and collected around Rs 3 Lakh," Shaikh said.

Vijay Kumar said that he stayed in Gujarat for ten days and collected Rs 3 Lakh with him.

"I had sought help from him. I stayed here in Gujarat for 10 days, and went with him from people to people and collected Rs 3 Lakh. No one lives like Hindus or Muslims in our village, everyone lives like friends," he said.

Months after the outbreak of COVID-19 in Wuhan city of central China, families of those deceased, who contracted the contagious infection, stood in long queues at funeral homes demanding to receive the cremated ashes of their loved ones.

Now this has spurred questions about the actual tally of COVID-19 related casualties in Wuhan, in a renewed pressure on the Chinese government that is already struggling to control its containment narrative of the pandemic spread.

Chinese media outlet Caixin showed how trucks carrying 2,500 urns with the ashes of the deceased COVID-19 cases were being shipped in a funeral home last week. Another picture published revealed how 3,500 urns were stacked within these funeral homes. It is therefore unclear how many urns have been filled in.

According to media reports, workers at several funeral parlors declined to provide any details as to how many urns were waiting to be collected, saying they either did not know or were not authorised to share the number.

Some families said they had been forced to wait for several hours to pick up the ashes. The photos circulated as mass deaths from the virus spiked in cities across the west, including Milan, Madrid and New York, where hospitals were erecting tents to handle the overflow as global infections soar past 500,000, with 24,000 dead.

According to Chinese government figures, 2,535 people in Wuhan have died of the virus. The announcement that a lockdown in place since January would be lifted came after the country said its tally of new cases had hit zero and stepped up diplomatic outreach to other countries hard hit by the virus, sending some of them medical supplies.

But some in China have been skeptical of the accuracy of the official tally, particularly given Wuhan's overwhelmed medical system, authorities' attempts to cover up the outbreak in its initial stages, and multiple revisions to the way official cases are counted.

Residents on social media have demanded disciplinary action against top Wuhan officials.

Many people who died had Covid-19 symptoms, but weren't tested and excluded from the official case tally, Caixin said. There were also patients who died of other diseases due to a lack of proper treatment when hospitals were overwhelmed dealing with those who had the coronavirus.

There were 56,007 cremations in Wuhan in the fourth quarter of 2019, according to data from the city's civil affairs agency. The number of cremations was 1,583 higher than those in the fourth quarter of 2018 and 2,231 higher than the fourth quarter of 2017.

Two locals in Wuhan who have lost family members to the virus said online that they were informed they had to be accompanied by their employers or officials from neighborhood committees when picking up the urns, likely as a measure against public gatherings.

COVID-19 is affecting 199 countries and territories around the world. Over 664,000 coronavirus cases have been registered globally out of which 30,890 have succumbed to the infection.