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Leading physicians are celebrating a small dose of good news that arrived Tuesday about dexamethasone, a cheap and widely used steroid shown to be able to save lives among COVID-19 patients, but also cautioning against releasing study results by press release during a global health emergency, like in the case of the latest dexamethasone study by University of Oxford.

"It will be great news if dexamethasone, a cheap steroid, really does cut deaths by one-third in ventilated patients with COVID19, but after all the retractions and walk backs, it is unacceptable to tout study results by press release without releasing the paper", Atul Gawande, surgeon and CEO of Haven Healthcare, tweeted.

"Bottom line is, good news," Dr. Fauci, America's foremost infectious diseases expert told a US newswire on Tuesday, soon after the dexamethasone results were announced in the UK.

Fauci, who has long championed the therapeutics-first view said that dexamethasone is a "significant improvement" in the available therapeutic options currently available.

On Medical Twitter and Facebook, doctors broadly agree that dexamethasone use aligns well with the way COVID19 attacks the body's immune system. Fauci said the results in the Oxford study make "perfect sense" in that context.

"We should see the number of people who actually survive go up, if the study holds up," virologist and epidemiologist Dr. Joseph Fair told a television network.

Global coronavirus cases crossed 8 million on Tuesday. In the US, Texas and Florida are facing a new wave of cases after lifting lockdown orders earlier than medical experts recommended. Amidst the relentless graph upwards, the dexamethasone study results injected hope for better survival rates among those most seriously ill.

World Health Organization chief scientist Soumya Swaminathan welcomed the results from the randomised control trial.

Dr Eugene Gu, Founder and CEO of CoolQuit tweeted that he is "genuinely impressed" with the UK dexamethasone trial. This may be a "game changer", he wrote.

"There's no conflict of interest as dexamethasone is a generic steroid. The mechanism of action makes sense because steroids can reduce cytokine storms and overactive immune systems that makes COVID-19 so deadly. The number needed to treat is 8 ventilated patients which is great."

The Oxford study found that dexamethasone reduced deaths by 35 percent in patients who needed treatment with breathing machines and by 20 percent in those only needing supplemental oxygen. Dexamethasone was one of 5 drugs studied in a large clinical trial in the United Kingdom named RECOVERY, short for Randomised Evaluation of COVID-19 Therapy.

Peter Horby, chief investigator of the University of Oxford clinical trial, said dexamethasone is the first drug to be shown to improve survival in COVID-19. Details of the study have not been released. The trial organisers said they made their announcement via a news release because of "the public health importance of these results." According to Horby's public comments, there was a lot of initial resistance to studying steroids.

During the study, 2,104 patients were randomly selected to be given 6 milligrams of dexamethasone once a day (either by mouth or by intravenous injection) for 10 days. That group was compared with 4,321 patients who received the usual care alone.

Researchers estimated that dexamethasone would prevent one death for every eight patients treated while on ventilators and one for every 25 patients on extra oxygen alone.

UK experts have called the study results a breakthrough in the fight against the virus. The researchers have promised they would publish the results soon.

The first COVID-19 vaccine tested in the US revved up people's immune systems just the way scientists had hoped, researchers reported Tuesday -- as the shots are poised to begin key final testing.

No matter how you slice this, this is good news, Dr. Anthony Fauci, the U.S. government's top infectious disease expert, told The Associated Press.

The experimental vaccine, developed by Fauci's colleagues at the National Institutes of Health and Moderna Inc., will start its most important step around July 27: A 30,000-person study to prove if the shots really are strong enough to protect against the coronavirus.

But Tuesday, researchers reported anxiously awaited findings from the first 45 volunteers who rolled up their sleeves back in March. Sure enough, the vaccine provided a hoped-for immune boost.

Those early volunteers developed what are called neutralizing antibodies in their bloodstream -- molecules key to blocking infection -- at levels comparable to those found in people who survived COVID-19, the research team reported in the New England Journal of Medicine.

This is an essential building block that is needed to move forward with the trials that could actually determine whether the vaccine does protect against infection, said Dr. Lisa Jackson of the Kaiser Permanente Washington Research Institute in Seattle, who led the study.

There's no guarantee but the government hopes to have results around the end of the year -- record-setting speed for developing a vaccine.

The vaccine requires two doses, a month apart.

There were no serious side effects. But more than half the study participants reported flu-like reactions to the shots that aren't uncommon with other vaccines -- fatigue, headache, chills, fever and pain at the injection site. For three participants given the highest dose, those reactions were more severe; that dose isn't being pursued.

Some of those reactions are similar to coronavirus symptoms but they're temporary, lasting about a day and occur right after vaccination, researchers noted.

Small price to pay for protection against COVID, said Dr. William Schaffner of Vanderbilt University Medical Center, a vaccine expert who wasn't involved with the study.

He called the early results a good first step, and is optimistic that final testing could deliver answers about whether it's really safe and effective by the beginning of next year.

It would be wonderful. But that assumes everything's working right on schedule, Schaffner cautioned.

Moderna's share price jumped nearly 15 percent in trading after US markets closed. Shares of the company, based in Cambridge, Massachusetts, have nearly quadrupled this year.

Tuesday's results only included younger adults. The first-step testing later was expanded to include dozens of older adults, the age group most at risk from COVID-19.

Those results aren't public yet but regulators are evaluating them. Fauci said final testing will include older adults, as well as people with chronic health conditions that make them more vulnerable to the virus and Black and Latino populations likewise affected.

Nearly two dozen possible COVID-19 vaccines are in various stages of testing around the world. Candidates from China and Britain's Oxford University also are entering final testing stages.

The 30,000-person study will mark the world's largest study of a potential COVID-19 vaccine so far. And the NIH-developed shot isn't the only one set for such massive U.S. testing, crucial to spot rare side effects. The government plans similar large studies of the Oxford candidate and another by Johnson & Johnson; separately, Pfizer Inc. is planning its own huge study.

Already, people can start signing up to volunteer for the different studies.

People think this is a race for one winner. Me, I'm cheering every one of them on, said Fauci, who directs NIH's National Institute of Allergy and Infectious Diseases.

We need multiple vaccines. We need vaccines for the world, not only for our own country. Around the world, governments are investing in stockpiles of hundreds of millions of doses of the different candidates, in hopes of speedily starting inoculations if any are proven to work.

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.