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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.

Washington, Jun 6: Washington mayor Muriel Bowser on Friday renamed an area near the White House that has become the epicenter of anti-racism protests over the past week "Black Lives Matter Plaza" -- unveiling a giant street mural.

But in so doing, the African-American mayor piqued the ire of the very movement she was supporting, as well as of President Donald Trump.

The protests are focused on the May 25 death in Minneapolis of 46-year-old black man George Floyd while in police custody. A white officer kneeled on his neck until he lost consciousness.

That officer and three others are now in custody and facing charges -- second-degree murder for the kneeling officer, and aiding and abetting that crime for his colleagues.

Just north of the White House, the words BLACK LIVES MATTER were painted in huge yellow letters along the street leading to the presidential mansion, along with the symbol from the DC flag.

"The section of 16th street in front of the White House is now officially 'Black Lives Matter Plaza'," Bowser tweeted.

A city worker put up a new street sign with the name.

"Determination to make America the land it ought to be," she said on Twitter.

The corner of 16th and H is significant -- in a controversial incident on Monday, peaceful protesters gathered there were dispersed with tear gas.

Shortly afterwards, Trump walked from the White House to a nearby church for a photo op, during which he held the Bible in his hand.

"There was a dispute this week about whose street this is. Mayor Bowser wanted to make it abundantly clear that this is DC's street and to honor demonstrators" who protested on Monday, her chief of staff John Falcicchio tweeted.

Rose Jaffe, one of the artists in the collective that painted the BLACK LIVES MATTER sign, told AFP it was "about reclaiming the streets of DC."

But she added that Bowser "has to do more than just a photo-op -- she must carry on when this is washed away" on issues like police accountability.

Stars Like LeBron James praised her move on Twitter, but the local chapter of the Black Lives Movement balked, calling the mural a "performative distraction from real policy changes."

"This is to appease white liberals while ignoring our demands," it said on Twitter, saying Bowser had "consistently been on the wrong side" of the movement.

'We are well equipped'

The US government deployed a significant contingent of federal officers and National Guard troops from other states -- many of them not wearing any identifying garb or badges -- to handle protests in Washington.

Bowser had called up the local Guardsmen but the Justice Department moved to take partial control of peacekeeping, with Guard troops from as far away as Utah brought in.

In a letter to Trump dated Thursday and tweeted early Friday, Bowser called for "all extraordinary federal law enforcement and military presence" to be removed.

She said their deployment was "inflaming demonstrators and adding to the grievances of those who, by and large, are peacefully protesting for change and for reforms to the racist and broken systems that are killing black Americans."

"These additional, unidentified units are operating outside of established chains of command," she added.

"We are well equipped to handle large demonstrations and First Amendment activities," including the right to assemble, Bowser said.

Trump reiterated on Friday that authorities need to "dominate the streets," and has been unapologetic about the deployment of forces.

And on Twitter, he lashed out at Bowser, calling her "incompetent" and saying the National Guard had saved her from "great embarrassment."

Senator Mike Lee of Utah accused Bowser of evicting Utah National Guard members from area hotels.

She replied: "DC residents cannot pay their hotel bills. The Army can clear that up with the hotel today, and we are willing to help."

New Delhi, May 22: The number of COVID-19 cases averted due to the lockdown is in the range of 14-29 lakh, while the number of lives saved is between 37,000 and 78,000, the government said on Friday citing various studies, and asserted that the unprecedented shutdown has paid “rich dividends” in the fight against the pandemic.

The lockdown in India has been a timely, graded, proactive and pre-emptive public health measure to fight the COVID-19 pandemic and has been part and parcel of the government’s overall strategy, Dr V K Paul, Member (Health), NITI Aayog, and Chairman, Empowered Group 1, said at a media briefing on the COVID-19 situation.

The government imposed the nationwide lockdown from March 25 to prevent the spread of the novel coronavirus and it is currently in its fourth phase.

Like the number of cases, the growth rate of number of COVID-19 deaths too has fallen significantly due to the lockdown, marking a notable difference between pre-lockdown and post-lockdown situations, he said.

At the briefing, Pravin Srivastava, Secretary, Ministry of Statistics and Programme Implementation gave model-based estimates on COVID-19 cases and deaths which have been prevented due to the lockdown.

As per Boston Consulting Group's model, the lockdown saved between 1.2 lakh and 2.1 lakh lives, while the number of COVID-19 cases averted is between 36 lakh and 70 lakh, he said.

According to Public Health Foundation of India, nearly 78,000 lives have been saved due to the lockdown, Srivastava said.

Citing a model by two independent economists, he said that around 23 lakh COVID-19 cases and 68,000 deaths have been averted due to the lockdown.

Some independent experts, including retired scientists, have calculated that around 15.9 lakh cases and 51,000 deaths have been averted due to the lockdown, Srivastava said.

A joint study by the Ministry of Statistics and Programme Implementation and the Indian Statistical Institute found that around 20 lakh COVID-19 cases and 54,000 deaths were averted due to lockdown, he said.

The number of COVID-19 cases averted due to the lockdown is in the range of 14-29 lakh, while the number of lives saved is between 37,000 and 78,000, the official said.

“We are fully confident that the lockdown, with full public cooperation, has reaped rich dividends,” Srivastava said.

The strong defence of the lockdown, comes a day after the health ministry said the period of lockdown has been gainfully utilized to ramp up the health infrastructure, with around 3,027 dedicated COVID-19 hospitals and 7,013 care centres being readied across the country to fight the disease.

The announcement on Thursday came after some media reports questioned the country's preparedness to deal with the highly infectious disease.

"There are reports in a section of the media about some decisions of the government regarding the lockdown implementation and response to COVID-19 management. The period of the lockdown has been gainfully utilised to ramp up the health infrastructure in the country," the ministry had said.

Addressing the press briefing on Friday, joint secretary in the health ministry Lav Agarwal said 48,534 COVID-19 patients, which is about 41 per cent of the total cases, have recovered so far. As many as 3,234 patients have recovered in the last 24 hours, he said’

The COVID-19 mortality rate has dropped from 3.13 per cent on May 19 to 3.02 per cent as focus was on containment measures andclinical management of cases, Agarwal said.

An ICMR official said 27,55,714 tests for COVID-19 have been conducted till 1 pm Friday with 1,03,829 tests done in one day. Over 1 lakh tests for COVID-19 have been done each day for the last four days, the official said.

The growth rate of novel coronavirus cases witnessed a steep decline from Apr 4 when lockdown put a brake on the speed of increase of cases, V K Paul said.

The number of COVID-19 cases would have risen exponentially had the lockdown not been implemented, he said, adding that the doubling rate of cases was 3.4 days when the lockdown started and it is 13.3 days at present.

The COVID-19 outbreak in India has remained confined to limited areas with 80 per cent of active cases in just five states, Paul said

He said around 80 pc of COVID-19 deaths have been in Maharashtra, Gujarat, Madhya Pradesh, West Bengal and Delhi.