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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.

Follow latest updates on the Covid-19 pandemic here

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, Apr 21: India's count of positive coronavirus cases reached 18,985 after 1,329 new cases were reported in the last 24 hours, the Ministry of Health and Family Welfare said on Tuesday.

Out of the total cases, 15,122 are active cases, 3,259 have been discharged or cured and one has migrated. With 44 new deaths reported in the last 24 hours, the toll stands at 603.

As per the evening update by the ministry, Maharashtra continues to be the worst-hit state with 4,669 cases, out of which 572 patients have been discharged and cured and 232 deaths.

Delhi's total count of confirmed cases stand at 2,081, which includes 431 cured or discharged cases and 47 deaths.

Gujarat has reported a total of 2,066 positive COVID-19 cases, out of which 131 patients have recovered or discharged, while 77 patients have lost their lives.

Madhya Pradesh's count of COVID-19 cases stand at 1,540, including 127 cured or discharged cases and 76 deaths.

Rajasthan has so far reported 1,576 positive cases, out of which 205 patients have recovered or discharged and 25 people have lost their lives.

Tamil Nadu's COVID-19 figure has risen to 1,520, with 457 patients recovered and 17 fatalities. Uttar Pradesh has reported 1,294 cases, out of which 140 patients have recovered and 20 are dead.

Washington, Jun 26: The US is reviewing its global deployment of forces to ensure it is postured appropriately to counter the People's Liberation Army, given the increasing threat posed by China to Asian countries like India, Malaysia, Indonesia, and the Philippines, Secretary of State Mike Pompeo said on Thursday.

Mr Pompeo made those remarks in response to a question during the virtual Brussels Forum 2020 of the German Marshall Fund.

"We're going to make sure we're postured appropriately to counter the PLA. We think that the challenge of our times, and we're going to make sure we have resources in place to do that," Mr Pompeo said.
 
The force posture review is being done at the direction of President Donald Trump, as part of which the US is reducing the number of its troops in Germany from about 52,000 to 25,000, he said.

Mike Pompeo said that the force posture would be dictated by the ground realities.

"In certain places there will be fewer American resources. There'll be other places - I just talked about the threat from the Chinese Communist Party, so now threats to India, threats to Vietnam, threats to Malaysia, Indonesia, South China Sea challenges, the Philippines," he said.

"To the extent that that changed, the difference in what the US decided to do impacts adversely a threat some place, it may be that other nations need to step up and take responsibility for their own defense in ways that they hadn't done previously. So, we want to do this in full consultation with all of our partners all around the world, and certainly our friends in Europe," Mr Pompeo said.

President Trump is being criticised for reducing troops from Germany. His critics say that this will increase the threat from Russia to Europe.

Mike Pompeo, however, did not agree with that argument.

It has been a long time since there has been a strategic review of our force posture all across the world. The US undertook that starting about 2.5 years ago, whether that was our forces in Africa, our forces in Asia, the force we have in the Middle East and in Europe, he said.

"We began to say these are often decisions that were made in a different time. Should we reallocate those a different way? Should we have a different composition of those forces? Everyone always wants to talk about ground troops. I get it. I was a young tank officer. You described that. There's nothing I like as much as a good M1 tank.

"But it's often the case that the capacity to deter Russia or other adversaries isn''t determined any longer by just having a bunch of folks garrisoned someplace. So, we really went to back fundamentally relook, what is the nature of the conflict, what''s the nature of the threat, and how should we allocate our resources, whether that''s our resources in the intelligence community, our resources from the Air Force or the Marines and Army," Mr Pompeo said.

Last week, Mike Pompeo criticised the Chinese Army for "escalating" the border tension with India and militarising the strategic South China Sea. He also described the ruling Communist Party of China (CPC) as a "rogue actor".

"Our broad set of allocation of security apparatus, our ability to counter cyber threats, how do we allocate them? What''s the best way to do this? And the decision that you see the president made with respect to Germany is an outcome from a collective set of decisions about how we''re going to posture our resources around the world," said the top American diplomat on Thursday.

Changes in force posture is being taken in consultations with allies and friends, Mr Pompeo said.

"President Trump has spoken to this. (Defense) Secretary (Mark) Esper will be in London today and in Brussels tomorrow. We''ll talk about our plan and how we''re thinking about delivering it," he said.

"But you should understand this, and I hope our European partners will understand this as well. When you see what we ultimately conclude, how we ultimately deliver on the statements of the president made, that they''re aimed squarely at what we believe to be democracies'' fundamental interest and certainly America's most fundamental interest," Mr Pompeo said.

Earlier this month, Mike Pompeo had said that China's actions, be it on the India border, or in Hong Kong or in the South China Sea, were part of the behaviour of the ruling Communist Party in Beijing in the recent past.

China has been fast expanding military and economic influence in the Indo-Pacific region, triggering concern in various countries of the region and beyond.

China is engaged in hotly contested territorial disputes in both the South China Sea and the East China Sea. Beijing has built up and militarised many of the islands and reefs it controls in the region. Both areas are stated to be rich in minerals, oil and other natural resources and are vital to global trade.

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