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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.

Singapore, Feb 24: Last week Singapore's Ministry of Trade and Industry revised their 2020 GDP growth projections downwards to -0.5 to 1.5 per cent, confirming fears of economic fallout from the coronavirus COVID-19. Just three days earlier, while visiting Changi Airport, the Prime Minister told the media that the country is bracing for a significant hit on the economy and the possibility of a recession.

In the budget announcement on February 18, various measures to help affected companies were announced.

This included a jobs support scheme to help companies retain workers that will see the government offset 8 per cent of wages up to SGD3,600(USD2,600) per worker, per month, for a three-month period. Companies will also get a 25 per cent rebate on their taxes for the year capped at SGD15,000 (USD10,800) per company.

There will be additional support for sectors directly affected by the virus outbreak such as tourism, aviation and retail. Qualifying companies will be given property tax rebates and can apply for temporary bridging loans to ease cash flow. Rebates will be offered on aircraft landing and parking charges as well as rental rebates for shops and cargo agents at Changi Airport.

Overall, the economic package will cost Singapore some USD 4.6 billion, well in excess of the USD 500 million some analysts had predicted. The resulting spending plan including the virus economic package will see a budget deficit of SGD 10.9 billion or 2.1 per cent of GDP, the highest since the Asian financial crisis of 1997.

It is hoped that with financial support, companies in Singapore will not only be able to ride through the current rough patch but be able to position themselves better to take off once the economic crisis brought upon by the contagion is over.

Which then are the Singapore companies that can potentially ride out the current storm and emerge stronger?

Aviation and hospitality firms are among those most impacted by the virus outbreak and Singapore Airlines (SIA) comes to mind. SIA is a well-run company but has seen its share price fall about 5.2 percent since the beginning of the year. In the short term, revenue and profits will no doubt be affected but it will recover in the long run.

Hospitality sector companies like Ascott Residence whose main sponsor is Capitaland, Southeast Asia's largest landlord, and CDL Hospitality, have seen 1.5 and 5.5 percent (respectively) shaved off their share prices since the start of the year.

In reporting financial results for the quarter which ended in December on February 14, Alibaba CEO Daniel Zhang said that due to the virus, they are seeing large changes in buying patterns. With widespread home confinement, there is a growing demand for delivery services including online food and grocery delivery, as well as office apps and streaming entertainment.

Similarly, in Singapore, with more people staying and working from home, the three main food delivery services, Grab Food, Foodpanda and Deliveroo, are doing roaring business. All three are privately held.

In late January, as the scale of the outbreak became more apparent, investors began pouring money into health-product firms in Asia that they think will benefit from the virus outbreak.

Bloomberg reported that when Chinese pharmaceutical companies like Da An Gene Co, Xilong Scientific and Shanghai Kehua Bio-Engineering said they have developed kits for detecting the virus, their stocks soared to hit the 10 per cent daily limit. Firms manufacturing protection gear and air-cleaning equipment climbed more than 10 per cent in Japan, while Malaysian rubber gloves producers climbed at least 5 per cent.

Naturally, many would view that pharmaceutical companies that have the technology and expertise to develop drugs to treat patients with the virus or are able to develop a vaccine, would stand to benefit from the coronavirus outbreak.

Firms like and Johnson & Johnson, Pfizer, MSD, GlaxoSmithKline (GSK) and Sanofi are the pharmaceutical behemoths that dominate the global vaccine market.

However, industry experts speaking to the BBC warned that a pot of gold is not necessarily waiting for any company that successfully develops a vaccine. Although the global vaccine market is expected to grow to USD60 billion this year, it is costly and time-consuming to develop and pass it through for use by the general public.

It is also unclear if Indian pharmaceutical firms will be able to benefit from the demand for medicines that can treat or prevent the virus.

India is the world's largest manufacturer of generic drugs and it supplies 20 percent of the world's drugs by volume. However, it sources 70 percent of its raw material from China. If supplies are disrupted beyond a month to a month and a half, they may see a slow-down in production. According to a CNN report, the companies that are most impacted by material shortages are GSK India, Pfizer (PFE) and Cipla. Other companies like Aurobindo Pharma, Cadila Healthcare and Sun Pharma are said to be carefully monitoring the situation.